Minilite Operation Manual

Minilite Operation Manual
Minilite
™
Operation Manual
3150 Central Expressway
Santa Clara, CA 95051
ph. 888-532-1064
ph. 408-727-3240
fax 408-727-3550
Service Department 877-272-7783
Continuum
Minilite User Manual
996-0220 Revision J
Copyright © 1997, 2005 by Continuum Electro-Optics, Inc. All rights reserved.
Printed in the U.S.A. Except as permitted under the United States Copyright Act of
1976, no part of this publication may be reproduced or distributed in any form or
by any means, or stored in a data base or retrieval system without the prior written
permission of Continuum.
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Table of Contents
Preface.................................................................................................................7
Préface.................................................................................................................9
Vorwort .............................................................................................................11
Introduction ......................................................................................................13
Chapter I Laser Safety Precautions ................................................................15
A. Class IV Laser safety precautions..............................................................15
B. General safety rules ...................................................................................15
C. Electrical safety rules ................................................................................16
D. Optical safety rules....................................................................................16
E. Safety features ...........................................................................................17
Interlocks...................................................................................................17
Laser covers...............................................................................................17
Exit shutter ................................................................................................17
F. Government and industry safety regulations .............................................17
G. Additional safety references ......................................................................18
Chapter II
Installation ..................................................................................25
A. Installation checklist..................................................................................25
B. Switching between 110 and 220 volt power ...............................................27
Chapter III Operation ....................................................................................29
A. Startup.......................................................................................................29
B. Shutdown...................................................................................................30
C. Operation...................................................................................................31
Firing single shots......................................................................................31
Low power operation .................................................................................32
Energy Attenuator......................................................................................32
Interlocks...................................................................................................32
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Resetting an interlock ................................................................................32
Using the cover interlock ...........................................................................33
External control .........................................................................................33
Synchronization .........................................................................................35
Tools required............................................................................................37
Optics required and beam polarizations .....................................................37
E. Installing optics and dichroics....................................................................38
Maximizing harmonic energy ....................................................................40
Chapter IV Maintenance................................................................................43
A. Cooling system..........................................................................................43
Draining and flushing the cooling water, Tower Supply ............................43
Draining and flushing the cooling water, Rack Mount Supply ...................45
Filling the cooling system..........................................................................48
Electrical system........................................................................................48
B. Optical maintenance ..................................................................................49
Tools and supplies .....................................................................................49
Inspecting and dusting optics .....................................................................49
Cleaning and replacing optics ....................................................................50
Replacing the flashlamp.............................................................................50
Chapter V Troubleshooting.............................................................................53
Chapter VI Theory ..........................................................................................55
A. Pulsed Nd:YAG lasers...............................................................................55
B. Q-switching ...............................................................................................55
C. Harmonic generation .................................................................................56
D. Output beam polarity .................................................................................57
Chapter VII Warranty.....................................................................................59
A. Express warranty .......................................................................................59
B. Limitations ................................................................................................59
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C. Returns, adjustments and servicing ............................................................59
D. Continuum service centers.........................................................................61
Notes ..................................................................................................................63
Chapter VIII
Minilite PIV............................................................................65
A. Particle Image Velocimetry .......................................................................65
B. Minilite PIV overview ...............................................................................65
PIV systems ...............................................................................................65
Beam quality..............................................................................................65
Stability .....................................................................................................66
Ease of use.................................................................................................66
Safety ........................................................................................................66
Lifetime .....................................................................................................66
C. PIV optical description ..............................................................................67
D. PIV operation ............................................................................................68
Startup .......................................................................................................68
Shutdown...................................................................................................69
E. Dual beam overlap and power balancing....................................................69
Adjustable optics .......................................................................................69
Beam overlap.............................................................................................69
Beam power balance ..................................................................................70
F. PIV pulse timing .......................................................................................70
Total flexibility..........................................................................................70
Simultaneous flashlamps ...........................................................................71
Internal flashlamp control ..........................................................................71
Internal control ..........................................................................................71
Maintaining PIV optics ..............................................................................71
Replacing the SHG crystal .........................................................................72
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Preface
The internationally recognized warning symbols shown here are used
throughout the manual to alert the user of potential hazards when
operating this laser.
LASER RADIATION:
The radiation symbol is to alert the user to the danger of laser radiation
when performing certain operations and when the danger of exposure is
the greatest. It is also used when the optical hazards are present.
DANGEROUS VOLTAGE:
The lightning or thunderbolt indicates the presence of high voltage
which may pose a danger to the user or the equipment.
CAUTION:
The exclamation point symbol is to draw attention to other potential
hazards not included under the optical or electrical categories. The user
should be aware of special care that needs to be taken when performing
potentially hazardous procedures.
WARNING! PERSONAL INJURY
The Safety section is placed as the first chapter of the manual to
emphasize its importance and the need for everyone to read it before
working with the laser.
The installation section includes a copy of the installation instructions
for future reference. The site requirements are listed as is the initial
installation process step by step.
The Operation section begins with the daily startup and shutdown
procedures. The single shot operation is discussed here too. The LED
status information and external control are explained. A description of
the installation and removal of the harmonics is given in Chapter III.
Instructions for careful cleaning of optics, replacing flashlamps and
replacing of cooling group filters are given in the Maintenance section.
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The Troubleshooting chapter presents common problems that are
encountered and ways to solve them in both the electronic and optical
areas. It is here that the more complicated procedures such as
eliminating free-running are discussed.
The Appendix lists the Continuum warranty and gives Service
telephone and FAX numbers for further help. The Operator Notes gives
the user a convenient place to keep maintenance records and other
information.
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Préface
Les symboles de danger reconnus internationallement présentés ici sont
utilisés tout au long du manuel pour avertir l’utilisateur des risques
possibles lors de l’utilisation de ce laser.
Le symbole de radiation sert à avertir l’utilisateur du danger
d’exposition à la radiation laser lors de l’exécution de certaines
opérations et lorsque ce danger est le plus grand. Il est aussi utilisé en
cas de risques optiques.
Le signe d’éclair indique la présence d’une haute tension qui peut
représenter un danger pour l’utilisateur ou l’équipement.
Le point d’exclamation sert à attirer l’attention sur d’autres risques
possibles non inclus dans les catégories optique et électrique.
L’utilisateur devrait être conscient des mesures de protection
particulières à prendre lors de l’exécution de procédures
potentiellement dangereuses.
La section Sécurité est en tête du premier chapitre de ce manuel afin de
souligner son importance et la nécessité incombant à chaque utilisateur
de la lire avant de commencer à utiliser un laser.
La section Installation comprend une copie des instructions de montage
pour future référence. Les exigences de site sont énumérées comme
l’est le processus d’installation initial, étape par étape.
La section Fonctionnement commence avec les procédures de mise en
route et mise en arrêt quotidiennes. Le fonctionnement en décharge
unique est aussi expliqué dans cette section. Une description de la mise
en place et de l’élimination des harmoniques commence dans la section
III.
Des instructions pour un nettoyage soigneux des éléments optiques,
pour le remplacement de la lampe éclair et des filtres du dispositif de
refroidissement se trouvent dans la section Entretien.
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Le chapitre Dépannage présente les problèmes couramment rencontrés
et indique les mesures à prendre dans les domaines de l’électronique et
de l’optique. C’est aussi dans ce chapitre que les procédures plus
complexes telles que l’élimination du fonctionnement libre sont
expliquées.
L’Annexe décrit la garantie Continuum et fournit les numéros de
téléphone et de fax du service après-vente. Les Notes de l’Utilisateur
offrent à l’utilisateur un endroit pratique pour conserver les rapports
d’entretien et d’autres informations utiles.
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Vorwort
Die hier abgebildeten, international verständlichen Warnsymbole
werden in der gesamten Anleitung dazu verwendet, den Benutzer auf
mögliche Gefahrenquellen beim Laserbetrieb hinzuweisen.
Das Strahlungssymbol warnt den Benutzer vor gefährlicher
Laserstrahlung bei bestimmten Betriebsverfahren und bei den stärksten
Strahlengefährdungen. Es wird auch für optische Gefahrenquellen
verwendet.
Das Blitzsymbol weist auf das Vorliegen von Hochspannung hin, die
eine Gefährdung für Benutzer oder Gerät darstellt.
Das Ausrufezeichensymbol soll auf weitere Gefahren aufmerksam
machen, die nicht unter die Kategorie Optik oder Elektrik fallen. Der
Benutzer sollte auf besondere Maßnahmen achten, die bei evtl.
gefährlichen Verfahren anzuwenden sind.
Das erste Kapitel dieser Anleitung ist der Sicherheitsabschnitt, da
dieser äußerst wichtig ist und vor dem Betreiben des Lasers von jedem
Benutzer gelesen werden sollte.
Der Abschnitt zur Installation enthält für den zukünftigen Bedarf ein
Exemplar der Installationsanleitung. Hier sind sowohl die
Standortanforderungen als auch eine schrittweise Erläuterung der
Erstinstallation enthalten.
Der Abschnitt zum Betrieb beginnt mit der täglichen Einschalt- und
Abschaltroutine. Außerdem werden der Einzelpulsbetrieb behandelt
und die Leuchtdioden-Statusinformationen und -Fehlermeldungen
erläutert.
Anweisungen zur sorgfältigen Reinigung der Optik, zum Austauschen
der Blitzlampen und der Filter der Kühlgruppe sind im
Wartungsabschnitt enthalten.
Das Kapitel Fehlersuche und -behebung beschreibt bekannte Probleme
(Elektronik und Optik), die auftreten können, sowie
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Abhilfemaßnahmen. Hier werden auch kompliziertere Verfahren, wie
das Verhindern von “Freischwingern”, erörtert.
Der Anhang enthält die Continuum-Garantie sowie ServiceRufnummern und -Faxnummern, unter denen weitere Hilfestellung
verfügbar ist. Unter “Benutzernotizen” kann der Benutzer bequem
Wartungsdaten und sonstige Informationen aufbewahren.
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Introduction
This manual covers the entire Minilite™ family of products.
These include:
•
Standard Minilite laser system with Tower-style power supply
•
Optional Rack mount power supply
•
Optional harmonics generators
•
Optional PIV configuration
Except where noted, the features and procedures described for the
standard Minilite configuration apply to all optional configurations.
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Chapter I
Continuum
Laser Safety Precautions
A. Class IV Laser safety precautions
Continuum’s Minilite Nd:YAG laser is a Class IV high power laser
whose beam is, by definition, a safety and fire hazard. Take precautions
to prevent accidental exposure to both direct and reflected beams.
Diffuse as well as specular beam reflections can cause severe eye and
skin damage. The 1064 nm, 355 nm and 266 nm outputs of a Nd:YAG
laser are invisible, making them even more dangerous. Infrared
radiation passes easily through the cornea, which focuses it onto the
retina, where it can cause instantaneous permanent damage or
blindness. Even small doses from scattered radiation can be harmful.
AVOID EYE AND SKIN EXPOSURE TO DIRECT OR
SCATTERED RADIATION.
B. General safety rules
WARNING!
If the equipment is used in a manner not specified
by the manufacturer, the protection provided by
the equipment may be impaired.
•
Locate the laser in a locked area with access only by authorized
personnel. Mark the area with well-defined warning signs,
making it off limits to unauthorized personnel.
•
Provide interlocks for all doors.
•
Shut off or place the laser in standby when not in use.
•
Remove volatile substances in the lab, which the laser could
ignite.
•
Place a fire resistant background behind target areas.
•
Coat surrounding work areas with a radiation absorbing material.
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C. Electrical safety rules
•
Turn off all power before beginning maintenance or repair.
•
Avoid the high voltages, which are present in the laser cavity and
Power Supply whenever the Minilite is on.
•
To prevent accidents due to electrical shock, care should be
taken to be sure the capacitors are completely discharged and the
power turned off before any maintenance or repairs are made to
the system. Electric shock and burns resulting from input power
or capacitor discharge can cause serious injury or death.
D. Optical safety rules
•
Eye safety is the greatest concern. This is a Class IV laser, the
highest and most dangerous classification. Even a main beam
reflection from a polished surface can cause severe and
permanent eye damage. Never look at a beam or reflection
directly.
•
Always wear laser goggles appropriate for the wavelength and
beam intensity generated.
•
Do not wear or use any object that may reflect laser light such as
a watch, ring, pen, reflecting tool, etc.
•
Light the area around the laser so that the operator’s pupils are
constricted normally.
•
Operate the laser without its covers only when adjusting it;
replace and rebolt covers promptly.
•
Always use the LOW ENERGY MODE when the laser head
cover is off.
•
Expand the beam wherever possible to reduce beam intensity.
•
Close beam exit shutter when laser is not in use.
•
Use an infrared detector or energy detector to verify that the
laser beam is off before working in front of the laser.
•
Set up experiments so the laser beam is not at eye level.
•
Provide enclosures for beam paths whenever possible.
•
Avoid blocking the output beam or its reflection with any part of
the body.
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E. Safety features
Interlocks
The Minilite has interlock switches which stop it from firing when the:
• Laser head (rod) temperature is too high
•
Laser head cover is open
•
Cooling water flow too is low
•
External interlock (if installed) is open.
All interlocks must be OK before the Minilite will fire. If any of them
or the external interlock is tripped, the yellow INTERLOCK LED will
light and laser firing will stop; it must be reset (Chapter III) before the
laser will fire again.
You may also wire your Minilite so that opening a door to the laser
laboratory (or opening any other switch) shuts off the laser. To install
an external interlock, see Chapter III.
Laser covers
Covers protect against stray laser radiation from the Minilite. Interlocks
prevent laser operation when they are open. Do not remove them or
defeat the interlock.
Exit shutter
The Minilite has an exit beam shutter located outside its housing.
Closing the beam shutter merely prevents the beam from exiting; it
does not shut down the laser.
F. Government and industry safety regulations
Continuum strongly suggests that all its customers purchase a copy of
the American National Standard for the Safe Use of Lasers (ANSI
Z136.1-1993) in order to read and implement necessary precautions.
The American National Standards Institute (ANSI), a member of the
International Organization for Standardization (ISO) and the
International Electrotechnical Commission (IEC), issues this booklet.
Write or call the publisher listed below for information on obtaining a
copy of ANSI Z136.1-1986.
Continuum’s user information complies with 21 CFR 1040.10
concerning laser safety.
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G. Additional safety references
Regulations of the Administration and Enforcement of the Radiation
Control for Health and Safety Act, 1968. US Dept. of Health and
Human Services, Public Health Service and FDA, April 1988.
Regulation JIS C 6802, May 1, 1991 (Japan, based on the section
1040.10 of 21 CFR regulation of the United States cited on the
previous page)
American National Standard for the Safe Use of Lasers. Laser Institute
of America, 1986.
Laser Safety Guide. Laser Institute of America, 1977.
A Guide for Control of Laser Hazards. American Conference of
Governmental Industrial Hygienists, 1976.
EN61010-1.
Figure 1.1
Minilite dimensions
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Figure 1.2
Table of labels used
Description
Image
Caution
A
High Voltage label
High Voltage
CAUTION: HIGH VOLTAGE
B
High Voltage cable label
BEFORE WORKING ON THIS UNIT,
------SWITCH OFF POWER SUPPLY,
------DISCONNECT ALL PLUGS.
C
Laser aperture warning
D
Laser indicator
310-0028 Rev. B
LASER A
310-0209 rev B
E
Laser indicator
LASER B
310-0210 rev B
F
Laser interlock warning
G
CDRH Class IV label
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Interlock defeated warning
H
I
Serial number tag
J
Laser Radiation symbol
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Figure 1.3
Label location diagram A
Exit shutter
C
G
Front view
“LASER ON” LED
F
J
Rear view
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Figure 1.4
Label location diagram B
B
F
Rear view of standard
laser head
J
“LASER ON” LED
G
F
F
A
A
I
JJ
F
F
D
J
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E
E
Rear view of PIV
laser head
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Figure 1.5
Power Supply label location diagram C
B
D or E label on
each power
supply
B
C
G
A
I
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Chapter II
Continuum
Installation
DANGER! High voltages and currents
The laser head and Power Supply contain
LETHAL VOLTAGES AND CURRENTS. Never
operate the laser with the Power Supply cover
removed
DANGER! Laser radiation
Observe all Chapter I safety precautions,
especially when the laser head cover is open.
When it is open, operate the laser only in LOW
ENERGY mode.
A. Installation checklist
1) Prepare the site for the laser; refer to Chapter I safety rules.
2) Inspect the crates upon arrival for shipping damage and
notify the shipper if any damage is visible.
3) Unpack the Minilite and check that all parts are present as
listed in the Final Test Report. Notify Continuum customer
service if any parts are missing. If any damage is found,
notify both the shipper and Continuum Customer Service
immediately.
4) Check all parts for shipping damage. Any shipping damage
is the responsibility of the shipping company and buyer.
Also open both laser covers and check for loose parts.
5) Set the equipment in place, considering all safety issues
(Chapter I).
6) Attach the high voltage cable from the laser head onto the
plug on the rear of the Power Supply.
7) Plug the BNC cable from the laser head into the Q-SW
TRIGGER BNC connector to the right of the high voltage
connector on the rear of power supply.
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8) Use the CHASSIS GND wing nut to ground the power
supply to the same ground used by other equipment
associated with the laser.
9) Connect the two water lines to the Power Supply nipples.
You may connect either water hose to the COOLING
WATER IN line.
10) Fill the cooling water reservoir (see Chapter IV,
Maintenance).
11) Remove any packing material around or under the cooling
fans in the power supply, and replace the power supply
cover.
12) Install an external interlock (optional). To install, wire a
switch between the two pins of the 2-pin Molex connector
plugged into the INTLK socket on the rear of the power
supply. When this switch is open, the Minilite will not fire.
Use switches and wiring rated at least 50 volts Vac at 0.1 A.
Note:
Short the Molex connector’s two pins together and
plug it into the INTLK socket when not using an
external interlock.
13) Verify that ACV selected corresponds to ACV you will
provide.
•
If switching between 110 VAC and 220 VAC (single
phase) operation, be sure to replace the line fuse, located
at the bottom of the AC INPUT plug, just below the
power plug on the rear of the Power Supply.
•
Check which fuse is installed by examining the arrows
on the fuse holder cover plate. To replace, first pry off
the cover plate. After installing the correct fuse, replace
the cover plate making sure that it is oriented so that its
arrow indicates the correct operating voltage. No other
change is needed.
14) Connect Power Supply to AC power. The Minilite requires a
single 15 amp outlet, 50 to 60 Hz.
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B. Switching between 110 and 220 volt power
If switching between 110 Vac and 220 Vac (single phase) operation, be
sure to replace the line fuse located at the bottom of the AC INPUT
plug, just below the power plug on the rear of the Power Supply
(Figure 2.1). Check which fuse is installed by examining the arrows on
the fuse holder cover plate. To replace, first pry off the cover plate.
After installing the correct fuse, replace the cover plate, oriented so its
arrow indicates the correct operating voltage. No other change is
needed.
Figure 2.1
Rear View of Power Supply
Keep these switches set to INT
for normal operation; set to EXT
only when operating the laser
remotely; see Chapter III for
details
Provide TTL signals here for remote;
see Chapter III for details.
Use these signals to synchronize other
events to the laser.
Q-switch adjustment pot, see Chapter III
Wire a switch between these 2 pins; when
open, the laser will stop. Otherwise, short
them to each other.
Counts number of flashlamp shots.
Attach both cables from t laser
head during installation.
Attach cooling hoses to laser head;
connect either hose to the IN nipple.
Make sure you ground this power
supply properly!
This is the main power switch.
Normally, leave it on and control the
laser with the key switch.
You may use 110 or 220 VAC if you
use the correct voltage fuse.
Pry off this cover to replace the main
fuse. Replace if blown or when
changing between 110 V and 220 V
input. When replacing the cover, be
sure its arrows show the correct input
voltage.
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Figure 2.2 Cooling system,
side view.
screw-down
plug;
remove to
add
distilled water
water
OUT
water
IN
white deionizer
cartridge is behind
the water reservoir
water
reservoir
left side of Minilite electronics module
Left side of rack mount power supply
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Chapter III
Continuum
Operation
A. Startup
Start the laser only after completing the installation and understanding
the laser safety chapter thoroughly. Be sure all covers are closed and
the reservoir is filled with distilled water before starting. See also
Figure 3.1.
1. Open the exit shutter on the front of the laser head.
2. Turn the AC power on; the red AC POWER ON LED on
the front panel will light; see Figure 3.1.
3. Turn the key switch ON; the cooling fan and water pump
will start, the yellow STOP LED will light, and the red
LASER ON LED will light after blinking for eight
seconds.
4. Push the LOW ENERGY MODE key; its yellow LED
should light.
5. Use the UP and DOWN keys to choose a firing rate
between 1 Hz and 15 Hz as shown by the REP RATE
display.
6. Push the START button to start flashlamp and Q-switch
firing; low power laser light will now exit the laser head.
Verify the beam is correctly aligned after leaving the
laser; the yellow Q-SWITCH LED will flash with each
shot.
7. Switch to full energy mode by pressing the LOW
ENERGY MODE button again.
8. To fire single shots, connect the single shot cable to the
front panel BNC; now the Minilite fires 1 shot each time
you press the cable’s button. The flashlamp continues to
fire at the current REP RATE; the single shot occurs at
the next flash after the button is pushed.
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Note:
Pushing the single shot button for several seconds
will stop single shot operation and start lasing at
the set REP RATE. Pushing it again returns the
laser to single shot mode.
B. Shutdown
1. Push the STOP button (see Figure 3.1).
2. Close the exit shutter.
3. Turn the key switch to the OFF position. The laser is now
off. You may also wish to turn off the AC POWER switch
on the rear panel.
4. Remove the key to prevent unauthorized use.
5. If shutting down for more than 3 months, observe the
Caution below.
CAUTION!
To prevent algae from growing in the cooling
system, run the laser at least 15 minutes/week. If
you will not use the laser for more than 3 months,
Continuum suggests that you drain and flush the
cooling system; Chapter IV has details.
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Figure 3.1
Power supply front panel.
Push for reduced energy (2 - 4% );
when on, yellow LED lights.
Push to increase firing rate (up to 15 Hz).
Push to decrease firing rate (down to 1 Hz).
REP RATE
LOW ENERGY
MODE
Push to stop the laser at once;
press START to restart;
LED is yellow when stopped.
STOP
START
Push after turning key switch on;
(and waiting until LASER ON LED
lights - after ~8 sec more);
START LED is red when on.
Q-SWITCH
SINGLE SHOT
OFF
AC POWER ON
LASER ON
KEYSWITCH RESET
INTERLOCK
Yellow LED blinks at
each single shot.
Connect single shot cable here:
• push briefly for each single shot
• push for ~2 sec to return to normal operation
ON
Key switch:
• turn on to operate
(after turning on AC power;
LASER ON lights ~8 sec later)
• cycle off/on to restart
(after resetting an interlock)
• remove key to prevent use
• water pump, fan are off
(when key is off)
On when plugged in and line switch (rear panel) is on.
On when key switch is on; press START to begin.
If lit, cycle key switch off/on after
correcting interlock fault to reset.
Correct interlock fault when lit, then reset key switch.
C. Operation
Firing single shots
Pushing the button of the single shot cable, when it is attached to the
front panel SINGLE SHOT BNC, switches to single shot mode. Each
successive push fires a single shot. The flashlamps continue to fire at
the current REP RATE with the cable attached, and each shot will
occur during the next flashlamp cycle (see Figure 3.3). Keeping this
button depressed for ~2 seconds will return the Minilite to normal
firing mode.
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Low power operation
When the LOW ENERGY MODE key (Figure 3.1) is on, the Minilite
produces an output beam with 2-4% of normal power. Use this mode
when steering the laser’s output beam and when converting between
different harmonic options.
Energy Attenuator
When the attenuator and its associated dielectric polarizer are installed,
a lever projects through an opening in the top of the laser head, near the
output port. Moving the lever allows beam energies between ~4% and
100% of the maximum. The attenuator is uncalibrated; use a power
meter while adjusting it to achieve specific energies. This option
permits wide changes in output power while maintaining beam shape
and quality.
Interlocks
Your Minilite is equipped with four internal and one external interlock.
Internal interlocks sense when:
• Laser head temperature is too high
•
Laser head cover is open
•
Cooling system flow is too low
•
Cooling airflow is too low.
All interlocks must be OK before the Minilite will fire. If any of them
or an external interlock are tripped, the yellow INTERLOCK LED will
light and laser firing will stop; it must be reset (next) before it will fire
again.
You may also wire your Minilite so that opening a door to the laser
laboratory (or opening any other switch) shuts off the laser. To install
an external interlock, see Chapter II.
Resetting an interlock
If the laser is interrupted during operation by an interlock opening,
Correct the condition, which triggered the interlock: the front panel
INTERLOCK LED should go out (see Figure 3.1).
1. Turn the key switch OFF, then ON. The KEY SWITCH
RESET LED will go out and the LASER ON LED should
come on.
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2. Push START to resume normal, single shot or external
operation.
Using the cover interlock
You must disable the cover interlock to operate the laser without its
cover. After removing the laser head’s cover:
1. Use the bolt provided to attach the interlock flag (Figure
1.1) on top of the cover interlock (Figure 3.3).
2. To enable the cover interlock, unbolt the interlock flag
and store it and the bolt where you can find them again.
External control
Turning the rear panel FLASHLAMP and/or Q-SWITCH switches
from INT to EXT will disable the internally generated signals, which
respectively fire the flashlamp and/or open the Q-switch (Figure 3.2).
At the same time, these switches let the Minilite accept TTL signals
into the FLASHLAMP TRIG IN and Q-SWITCH TRIG IN BNC ports
to trigger flashlamp firing and Q-switch opening. To operate remotely:
1. Set the two INT/EXT switches as desired (see Table 3.1).
2. Start up the laser normally and push the START key.
Note:
The START LED is now on (indicating flashlamps
are on), the REP RATE reads 10 Hz and the single
shot LED blinks.
3. Provide TTL signals (0 to +5 Vdc, 10-20 µsec wide
pulses) to the FLASHLAMP TRIG IN and/or Q-SWITCH
TRIG IN ports.
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Flashlamp
Q-Switch
Int/Ext switch
Int/Ext switch
Operation Mode
INT
INT
Normal (internal) operation mode: front
panel and/or single shot controls laser firing
EXT
INT
TTL pulses sent to FLASHLAMP TRIG IN
BNC fire the flashlamp; the Q-switch
automatically opens after the same delay as
in normal operation. However, this method
introduces jitter in the laser pulse timing,
and pulse energy will be the same as in
normal mode.
INT
EXT
The flashlamps will fire at the rate set by
the front panel, but the Q-switch will open
only when a TTL pulse is sent to the Qswitch TRIG IN BNC. Timing accuracy is
better than in the above mode, but the
pulse energy may fluctuate more than in
normal mode. You may wish to use the
FLASHLAMP SYNC OUT pulse to time your
Q-SWITCH TRIG IN pulse.
EXT
EXT
You must send a pulse to both fire the
flashlamp, then another to open the Qswitch. This yields best accuracy in pulse
timing (minimum jitter) and most constant
pulse energy (constant Q-switch delay
time). Varying the time between flashlamp
firing and Q-switch opening affects pulse
energy.
Table 3.1
Internal and External Operation Modes
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Figure 3.2
Timing pulse sequences
Synchronization
You may synchronize events to Minilite laser pulses using signals
provided on the rear panel of its Power Supply. The Q-SWITCH SYNC
OUT signal is most closely synchronized to the laser pulse, which
occurs ~60 nsec after the Q-switch opens. Figure 3.2 shows the
approximate relationship between these two TTL signals and the laser
pulse.
These synchronization signals appear in all internal, single shot and
external operation modes.
Q-SWITCH
SOURCE
SYNC
TRIG
EXT
OUT
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I
INT
FLASHLAMP
SYNC
TRIG
SOURCE
EXT
OUT
IN
INT
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Figure 3.3 Optical layouts
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D. Generating 532, 355 and 266 nm output
The Nd:YAG Minilite laser produces horizontally polarized infrared
light at 1064 nm. Optional non-linear crystals in the beam can double,
triple, or quadruple the frequency of this fundamental, resulting in 532
nm, 355 nm or 266 nm light, respectively. These crystals do not convert
all of the fundamental beam to their output frequency, so the Minilite
uses pairs of dichroics (each pair matched to a crystal’s output) to
separate the output frequency from the residual input, and steer the
output through the exit port. Figure 3.3 shows arrangements of
dichroics and crystals for all outputs.
Switching between these wavelengths requires installing or removing
the crystals and their associated pair of dichroics, then optimizing the
energy of the resulting output beam. These operations are detailed in
the next 2 procedures, Installing optics and dichroics and Maximizing
beam energy.
Tools required
•
Safety glasses
•
Red fluorescent paper and a white business card
•
Metric Allen wrenches
•
Power meter with energy absorbing head
Optics required and beam polarizations
This table gives the combinations of crystals and dichroics required to
generate 532 nm, 355 nm and 266 nm light.
*1064 dichroic in different position for 1064 nm output
Table 3.2
Optics for all output beams .
output set of 1st
beam dichroics
1064 nm
1064*
532 nm
532
355 nm
355
266 nm
266
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first
crystal
none
532
532
532
second
crystal
none
none
355
266
set of 2nd
dichroics
1064
532
355
266
output
polarization
horizontal
vertical
horizontal
horizontal
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E. Installing optics and dichroics
For 1064 nm output, install the 1064 nm dichroic and use its H and V
adjustments to steer the beam out of the exit port (Figure 3.3). This
procedure describes 532 nm, 355 nm, and 266 nm optics installation.
WARNING!
This procedure requires operating the laser with its
cover removed. Wear safety goggles and observe
all safety rules.
1. Turn the key switch OFF and remove the laser head’s
cover.
2. Remove the proper crystal and pair of dichroics from
their storage positions inside the laser head (see Table 3.2
and Figure 3.3).
3. Remove any unneeded crystal(s) and dichroics. Bolt all
unused optics into storage positions (Figure 3.3).
4. Install the selected crystal(s) and dichroics; refer to
Figure 3.3 to orient the optics. Be sure to reposition the
1064 nm dichroic if switching from 1064 nm output.
5. Defeat the laser cover interlock and open the output
shutter.
6. Start the laser at 10 Hz in low energy mode.
7. Using red fluorescent paper, make sure the 1064 nm beam
passes through the 532 nm crystal without being clipped.
Use the H and V adjustments of the first 1064 nm
dichroic (Figure 3.4) to center the beam in the 532 nm
crystal.
8. If there is a 355 nm or 266 nm crystal present, use the H
and V screws of the second 1064 nm dichroic (Figure 3.4)
to center the beam in this crystal. Use a business card to
ensure the exit beam isn’t clipped.
9. Use the H and V adjustments of the second pair of
dichroics to steer the final beam through the center of the
exit port.
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10. Angle tune the crystal(s) and adjust the 532 nm half wave
plate (Figure 3.4) to maximize beam energy (see next
procedure).
11. Turn off the laser, remove the interlock flag, and replace
the cover.
12. Switch to high power mode and resume operation.
Figure 3.4a
Dichroic mounts
Vertical
adjustment
Note adjustments:
Remove both to
detach front plate to
replace an optic
Dichroic: clench front
plate to remove
When installing front
plate with new optic,
reinstall ball bearing
Mounting bolt
holes
Horizontal
adjustment
Figure 3.4b
Crystal mounts
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Maximizing harmonic energy
For maximum harmonic conversion, you must adjust the crystal
angle(s) and the 532 nm wave plate (Figure 3.4). All crystals are Type
II, meaning that their conversion efficiency is highly dependent on their
angle to the input light beam’s polarization plane.
Perform this procedure after installing any new crystal, or if output
energy is low. This procedure isn’t needed for 1064 nm output.
WARNING!
This procedure requires operating the laser with its
cover removed. Wear safety goggles and observe
all safety rules.
1. With the laser off, remove the laser head outer cover,
install the cover interlock defeat flag and open the output
shutter. Place the head of a power meter in the exit port.
2. Start the laser at 10 Hz in normal (high) energy mode, and
measure the beam energy with a power meter.
3. Turn the 532 nm crystal’s V adjustment to maximize
beam energy.
4. Unlock its half wave plate and rotate it slightly to
maximize energy.
5. Repeat the last two steps once or twice, until no
additional energy increase occurs.
6. If generating 532 nm or 266 nm light, re-tighten the half
wave plate’s locking screw. This completes the 532 nm
energy maximization.
7. If generating 266 nm or 355 nm light, move the second
crystal’s H adjustment screw to produce maximum beam
energy. This finishes the 266 nm maximization.
8. If generating 355 nm light, rotate the half wave plate
slightly to maximize energy.
9. Repeat the last two steps once or twice, until no
additional energy increase occurs.
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10. Turn off the laser, remove its interlock flag and replace
the cover.
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Chapter IV Maintenance
A. Cooling system
Circulate water through the cooling system by turning on the laser (turn
on the ac power) for ~30 seconds every week when the laser in not in
use.
Insure that the reservoir’s water level is always at least 75% full. If the
water level is low, top off the reservoir with distilled (not deionized)
water. To check, unplug the power supply and remove its cover. Figure
4.1 shows the location of the water reservoir.
The Minilite is shipped without water. Be sure to fill the cooling
system upon installation; a water flow interlock prevents operation
without water.
CAUTION!
If not using the Minilite for 3 months or more,
drain the cooling water and then flush the laser
head with methanol.
Draining and flushing the cooling water, Tower Supply
This procedure is for the standard tower power supply. See the
following section for the procedure for the rack mount supply.
Drain the cooling system before replacing its deionizer or before
storing the laser. Also flush the head with methanol before storage (DO
NOT flush DI cartridge with methanol.)
1. Shut down the Minilite, unplug it and close its exit beam
shutter.
2. Remove the power supply cover and unscrew the
reservoir filler cap (See Figure 4.1).
3. Disconnect the water hose from the power supply
RETURN coupling; attach a piece of scrap hose and put
its other end in a waste bucket.
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4. Plug in the power supply and turn on the ac power to run
the cooling pump until no more water appears; turn off
the power.
5. Using gentle air pressure (<10 PSI) on the disconnected
RETURN hose coupling, blow any remaining water from
the laser head into the reservoir.
6. Turn the ac power on again briefly to pump this water
away.
7. If storing the Minilite more than 3 months, remove both
water hoses from the power supply. Then pour 20-30 ml
of methanol into the OUT hose leading to the laser head
(tubing and a syringe or a funnel will make adding
methanol easier). Follow with gentle air pressure (-5 psi)
to blow the solvent out of the head. This methanol flush
prevents algae buildup.
8. If refilling, refer to the previous procedure, and also
replace the deionizer cartridge (next procedure).
9. Reconnect all water hoses and replace the power supply
cover.
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Figure 4.1
Cooling system
Draining and flushing the cooling water, Rack Mount Supply
This procedure is for the rack mount power supply. See the preceding
section for the procedure for the standard Tower supply.
Drain the cooling system before replacing its deionizer or before
storing the laser. Also flush the head with methanol before storage.
10. Shut down the Minilite, unplug it and close its exit beam
shutter.
11. Connect a piece of scrap tubing to the fill port on the
front panel of the supply (See Figure 4.2).
12. Disconnect the water hose from the power supply
RETURN coupling; attach a piece of scrap hose and put
its other end in a waste bucket.
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13. Plug in the power supply and turn on the ac power to run
the cooling pump until no more water appears; turn off
the power.
14. Using gentle air pressure on the disconnected RETURN
hose coupling, blow any remaining water from the laser
head into the reservoir.
15. Turn the ac power on again briefly to pump this water
away.
16. If storing the Minilite more than 3 months, remove both
water hoses from the power supply. Then pour 20-30 ml
of methanol into the OUT hose leading to the laser head
(tubing and a syringe or a funnel will make adding
methanol easier). Follow with gentle air pressure (-5 psi)
to blow the solvent out of the head. This methanol flush
prevents algae buildup.
17. If refilling, refer to the previous procedure, and also
replace the deionizer cartridge (next procedure).
18. Reconnect all water hoses and replace the power supply
cover.
Figure 4.2
Rack Mount Supply cooling system
Low flow rate
interlock sensor
Retaining Clip
Heat exchanger
Page 46
DI Filter
Pump
Reservoir
Fill port
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Replacing the deionizer cartridge
Replace the deionizer cartridge (p/n 309-0309) and the cooling water
every six months. To replace the cartridge;
1. Drain the cooling system (above), but don’t replace the
cover.
2. Turn the ac power switch off, and then unplug the power
supply.
3. Pull down the old cartridge to remove it from its retaining
clip. Note float direction arrow.
4. Disconnect both hoses from the cartridge; quick-release
couplings secure both of them (push and rotate ¼ turn to
release)
• Remove quick connectors from old DI filter.
• Install quick connectors on new DI filter. It is
advised to replace Teflon tape on QC threads to
avoid leaks.
5. Attach the hoses to the new filter and push it into its
retaining clip.
Note:
The cartridge’s flow direction arrow should point
to the rear.
6. Refill the cooling system (next). While running the pump
(step 5 of the next procedure), check for water leaks
around the new cartridge.
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Filling the cooling system
Fill the cooling system before beginning operation (see Figure 4.1). To
fill:
1. Shut down the Minilite, unplug it and close its exit beam
shutter.
2. Remove the power supply cover and unscrew the
reservoir’s cap.
3. Replace the deionizer cartridge (above).
4. Fill the reservoir up to the cap with distilled (not
deionized) water. If empty, this requires ~10 oz (300 ml).
Use a syringe or tubing and funnel to minimize spillage.
5. Plug in the power supply and turn the ac power on for one
minute to run the water pump. Correct any leaks.
6. If the water level falls below 75% full, unplug the power
supply and repeat the last two steps.
7. If the head has been previously flushed with methanol,
drain the water again (previous page) and replace it a
second time.
8. Unplug the power supply, and then replace the reservoir’s
cap and the outer cover of the power supply.
Electrical system
A power line fuse is installed on the back panel near the power cord.
This table gives recommended fuses:
Manufacturer
100-125 VAC (3.0 A)
180-240 VAC (1.6 A)
Bussmann
MDL-4
MDL-2
Littlefuse
313.004
313.002
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B. Optical maintenance
Periodically inspect the crystals and coated surfaces of all optical
components for dust, discoloration, and damage, and clean or replace
them if necessary. Realign the beam (see Chapter III) after replacing
any optical element.
Tools and supplies
•
Finger cots or surgical or fine cotton gloves
•
High intensity flashlight and inspection mirror
•
Metric Allen wrenches (supplied)
•
Reagent grade (or better) methanol
•
Eyedropper
•
Lint-free lens tissues and cotton swabs
•
Flashlamp
Inspecting and dusting optics
Dust on optical surfaces absorbs laser light and the hot spot will burn
the surface. Follow these steps to dust the optics and determine whether
an optical surface needs cleaning or a component requires replacement.
1. Turn the key switch OFF and remove the laser and laser
head cover.
2. Systematically examine the surfaces of each dichroic,
crystal window and half wave plate for dust, fingerprints,
discoloration, and burn marks in the surface coating. Also
look at the crystals.
3. Use a bright flashlight to light the surfaces and eliminate
reflections, and an inspection mirror where needed.
4. Use clean compressed air to clear dust and loose debris on
surfaces.
5. Note which components need cleaning and which need
replacing. Do not use solvent unless compressed air is
inefficient.
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Cleaning and replacing optics
1. Wash your hands and put on gloves or finger cots.
2. Wrap lens tissue on a cotton tipped applicator. Apply a
few drops of solvent directly to the tissue; shake off any
excess.
3. Swab optic gently with the applicator. Repeat these steps
with a drier swab to remove remaining residue.
4. If damage is still visible, order a replacement optic (Table
4.1). Continuum will ship it already mounted. To replace
a mounted dichroic, remove the mount from the bench,
and unscrew both spring-loaded bolts on the back of the
mount. The plate with the optic will come free, as will a 4
mm ball bearing. When replacing the new plate, be sure
to re-install the ball bearing (See Figure 3.4).
Replacing the flashlamp
Replace the flashlamp (p/n 203-0041, “O”rings are p/n 306-0167) after
about 30 million shots, or if output beam energy has fallen below an
unacceptable level or firing has become erratic.
1. Drain the cooling system water (see the first page of this
Chapter).
2. Unplug the laser’s ac power cord, and then remove the
laser head cover.
3. Remove the cooling system hoses from the head (Figure
4.3).
4. Remove 5 wires from the laser head assembly (Figure
4.3):
4a. Pull the red and black flashlamp leads up to remove
them; one is at each end of the head, encased in a square
white insulator.
4b.Slip the thick red wire at the top center of the head out
of its connection post.
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4c. Remove the two thin wires from the head temperature
sensor, located on top of the head.
5. Remove the four recessed bolts that secure the Marx Bank
PCB from the optical bench, and then remove the four
more bolts, which hold the head assembly to the optical
bench. Remove the two wires to the Pockels cell, the
PCB, and finally, remove the head assembly.
6. Remove the three bolts from each triangular end piece
and slide the end pieces off the head assembly.
7. Slide the flashlamp forward to remove it from the head.
Note which end of the head has a red mark; it should be
the end connected to the red flashlamp lead. Also be sure
to remove both flashlamp “O”rings, on at each end of the
head assembly.
8. Wearing finger cots or clean white cotton surgical gloves,
clean the new flashlamp with methanol on a tissue.
9. Install the flashlamp with its red mark oriented properly
(Figure 4.3).
10. Slip a new “O”ring on each end of the lamp, and re-attach
the triangular end pieces.
11. Bolt the head assembly onto the optical bench then bolt
the Marx Bank onto the bench.
12. Re-connect the five wires: thin pair to the temperature
sensor, the two flashlamp leads at the ends, and a thick
red wire at top center.
13. Re-connect the water hoses and refill the water reservoir.
14. Plug in the power supply, turn the key switch on and turn
on the key switch to start the cooling system pump.
15. Look for leaks around the laser head. If no leaks occur,
turn the key switch off and replace both covers.
16. Restart the laser and examine the beam about 500 cm
from the exit port. If the beam seems to be clipped,
realign beam in LOW ENERGY mode (see Installing
optics and dichroics in Chapter III)
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Figure 4.3
Flashlamp details
Table 4.1
Selected Minilite part numbers
NAME
P/N
OUTPUT
1064 nm dichroic
532 nm crystal
355 nm crystal
266 nm crystal
532 nm dichroic (2)
355 nm dichroic (2)
266 nm dichroic (2)
Attenuator option, with waveplate
Deionizer filter
Flashlamp
Flashlamp “o” rings (2)
640-1020*
640-1110*
640-1210*
640-1310*
640-1120*
640-1120*
640-1320*
640-1800*
309-0309
203-0041
306-0167
All
All but 1064
355 only
266 only
532 only
355 only
266 only
All
All
All
All
* an assembly which includes the optic and its mount
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Chapter V Troubleshooting
WARNING!
Do not operate the laser with the covers of the
laser head or power supply removed. Laser
radiation andor high voltages are present inside of
the laser head and power supply. If after
following the guide below, the laser still does not
function, contact Continuum for assistance.
If beam energy is low or beam shape is clipped refer to Installing optics
and dichroics and Maximizing beam energy in Chapter III.
If the laser fails to operate, check the following:
1. Is the laser head’s high voltage cable and Q-switch trigger
cable both properly attached to the power supply?
2. Are both the AC POWER switch and the key switch on?
3. Is the power supply fuse OK?
4. Are both INT/EXT switches on the top rear of the power
supply back panel OFF?
5. Is the KEY SWITCH RESET LED on? Cycle the key
switch off, then on again.
6. If no external interlock is used, is the shorting Molex plug
installed in the INTLK socket (on the back of power
supply) in place?
7. If an external interlock is utilized, is its switch closed?
8. Is there adequate water in the cooling system? Are there
kinks in the water hoses?
9. Is the laser head cover properly installed, engaging the
cover interlock?
10. Is the yellow INTERLOCK LED on? If so, recheck all
interlocks:
Laser Head:
Power Supply:
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Rod Temperature too high
Water flow low
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External interlock:
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Door open or other switch open
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Chapter VI Theory
A. Pulsed Nd:YAG lasers
The Minilite uses traditional flashlamp pumping. Distilled water cools
the lamp and gain medium, reducing thermal lensing. When electrically
pulsed, the lamp emits light which excites the Nd:YAG gain medium.
Similar to a capacitor storing electrical energy, the Nd:YAG rod
absorbs the flashlamp’s optical energy. Neodymium atoms that have
been excited to a higher electronic state (the lasing level) store this
energy. These atoms remain excited for a fraction of a millisecond
before spontaneous emission starts.
In the absence of Q-switching, spontaneous emission (lasing, or light
amplification through stimulated emission) begins as soon as the cavity
gain overcomes its losses. The duration of this spontaneous laser pulse
is almost as long as the driving lamp pulse. This non Q-switched pulse
has high energy, but its peak power is low, because of its relatively
long width. The Minilite Q-switch improves performance by both
increasing the amount of energy stored in the rod and by preventing or
delaying spontaneous emission.
While closed, a Q-switch in the laser cavity introduces an additional
loss and blocks spontaneous emission, allowing the number of excited
atoms in the rod to build further. When instantaneously opened, it
releases the cavity’s stored energy in a shorter pulse with both higher
average and peak power.
B. Q-switching
A crystal, quarter wave plate and a horizontal polarizer, placed in the
laser cavity between its end mirrors, comprise a Q-switch. The lamp
pumps the gain medium while the Q-switch is closed (there is no
voltage applied to its crystal, and the crystal does not rotate light.)
While closed, light exiting the rod cannot return to stimulate
spontaneous emission, and the rod stores more energy. Vertically
polarized light exiting the gain medium never returns; it is always
blocked by the horizontal polarizer. When the Q-switch is closed, it
also blocks horizontally polarized light: this light passes unchanged
through the horizontal polarizer and the crystal, then rotates 45°
transiting the quarter wave plate. On its return path, it rotates another
45°. Now vertically polarized, the horizontal polarizer prevents it from
reentering the rod.
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After maximum storage occurs (about 200 microseconds after the lamp
begins pumping), the Q-switch opens: a Marx bank suddenly applies a
high voltage to the crystal. When so energized, the crystal now rotates
the light another 90° (45° in each direction through the Q-switch).
Horizontally polarized light now rotates a total of 180°, so it retains its
polarization traveling through the Q-switch, and can reenter the laser
rod. This light is now free to oscillate between the cavity end mirrors.
During these oscillations, the light increases in energy by extracting the
energy stored in the gain medium. The resultant laser pulse is 5-6
nanoseconds long, with high peak and total power.
C. Harmonic generation
The Minilite can produce laser light at other frequencies besides the
natural, or fundamental frequency of its Nd:YAG gain medium. In
some crystals, a non-linear process known as harmonic generation
produces additional frequencies which are multiples (double, triple,
quadruple, etc.) of the fundamental. Since the Minilite’s fundamental is
1064 nm, its second, third, and fourth harmonics are 532, 355 and 266
nm, respectively.
For a crystal to be suitable for harmonic generation, it must transmit
both the fundamental and the harmonic it produces, withstand high
peak intensity laser beams without damage, and convert the
fundamental to the harmonic efficiently. The Minilite employs KTP
and BBO crystals, widely know for their suitability, for harmonic
generation. Simply replace a crystal to change the Minilite’s output
frequency (Chapter III).
Non-linear materials transmit light at differing speeds, depending on
the light’s angle to the crystal’s non-linear axis and on the light’s
polarization relative to that axis. This second property is called
birefringence.
During doubling, two 1064 nm photons enter the crystal collinear and
with the same (circular) polarization. This would allow the two photons
to combine into a single photon, provided that the resulting photon
conserves both energy and momentum. A combined (doubled) photon
with doubled frequency satisfies energy conservation. Angular
momentum conservation gives the output photon a different (vertical)
polarization. Momentum conservation requires the combined photon to
have the same velocity as the incoming photon pair. In the non-linear
crystal, there is a particular angle (the phase matched angle), at which
the crystal’s birefringence equalizes the velocities of the input photons
and the differently polarized combined photon. Satisfying these three
conservation conditions permits doubling, provided that the two input
photons enter the crystal close together. The high peak power of the
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Minilite generates a sufficiently large photon density inside the crystal
for efficient doubling to occur.
Tripling (third harmonic generation) is a similar process, except that
one photon of the fundamental combines with one photon of doubled
light. The output of a doubling crystal contains these necessary two
photons. This twin beam enters another crystal, where the two different
photons combine (mix). The resulting photon’s energy (355 nm) is the
frequency sum of the two mixed photons (1/355 = 1/1064 + 1/532).
Quadrupling is simply a two-stage doubling process: the 532 nm output
of the doubling crystal enters a second doubling crystal, where it
doubles again.
D. Output beam polarity
The Minilite’s fundamental (1064 nm) output beam is always
horizontally polarized. Each harmonic crystal rotates the beam polarity
90°, giving the second harmonic beam vertical polarity. Since both the
third and forth harmonic require a second crystal, these output beams
have horizontal polarization. The Minilite PIV’s 532 nm beam is
circularly polarized.
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Chapter VII Warranty
A. Express warranty
Unless otherwise specified, all mechanical, electrical and electrooptical components are warranted to be free from defects in materials
and workmanship for 1 year after delivery to the FOB point. Optics,
crystals and flashlamps have a 90-day warranty.
This warranty is in lieu of all other warranties, express or implied, and
no warranties of Merchantability or fitness or any other remedies are
available.
B. Limitations
This warranty’s remedy is limited to repair or replacement of the
defective materials, and depends on these conditions:
•
This warranty does not apply to materials that have been
damaged by abuse, misuse, mishandling, accidental alteration,
improper operation, negligence or other conditions not under
Continuum’s control.
•
This warranty does not apply if the original identification
markings have been removed, defaced or altered, or if
modifications or substitutions have been made without
Continuum’s prior consent.
•
This warranty does not apply if the Customer’s account is
delinquent.
C. Returns, adjustments and servicing
To request any warranty or other repair or service to any Continuum
product:
•
Obtain a return authorization number from our Service Dept.
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•
Package properly in the original shipping container. Drain any
water from the cooling system. Pre-pay freight and full-value
insurance, and assume all risks of loss, damage, or delay in
shipment.
•
Continuum will examine the received laser to determine the
cause of failure and warranty status, and is not obligated to
perform a warranty repair if shipping damage obscures whether
the warranty defect existed.
•
The warranty period on a repaired or replaced product is the
remainder of the product’s original warranty period. If the
product is not under warranty, Continuum will advise the
customer of repair charges and require a written purchase order
for repairs before work begins.
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D. Continuum service centers
www.continuumlasers.com
Continuum®
3150 Central Expressway
Santa Clara, CA 95051, USA
Phone: (408) 727-3240
service@continuumlasers.com
Excel Technology Europe GmbH
Roentgenstrasse 84
D-64291 Darmstadt
Germany
Phone: 49 6151-9380-33
info@excel-europe.com
Excel Technology France S.A.S.
91600 Savigny-sur-Orge
France
Phone: 33 169-12-29-80
info@excel-france.com
Excel Technology South-Asia Pvt. Ltd.
A1-424 Shah & Nahar Industrial Estate
Lower Parel – Mumbai 400 013
India
Phone: 91 22 5660-5888
info@exceltech-southasia.com
Excel Technology Asia
Bayan Lepes F1Z, Phase 1
11900 Penang
Malaysia
Phone: 604 646-1002
inquiry@exceltechasia.com
Excel Technology Japan
2-53-4 Koenji-Minami
Suginami-Ku, Tokyo 166-0003
Japan
Phone: 81 3 5305-5313
continuum@exceltech-japan.com
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Notes
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Chapter VIII Minilite PIV
A. Particle Image Velocimetry
Particle Image Velocimetry (PIV) is a powerful method for monitoring
complex velocity distributions in complex media. Typical applications
include shear and laminar flows, exhaust plumes, and vehicular and
aircraft airflows.
The PIV process compares two images, separated in time, from a
scatterer injected into the airflow distribution. A Q-switched, pulsed
Nd:YAG laser beam, shaped by cylindrical optics, produces a sheet of
light which illuminates a cross-section of the flow medium.
Photographic film or a CCD camera is used to capture two consecutive
images of the scatter passing through this cross section. This “double
exposure” captures a wealth of information on the scattering particles’
velocities. The recorded data is deconvoluted using several correlation
integrals, achieving a complete two dimension velocity vector field for
large flow areas.
B. Minilite PIV overview
PIV systems
Continuum’s Minilite PIV systems are designed for stability, beam
quality, and variable pulse separation. The Minilite PIV contains two
Minilite laser heads mounted on a stable, compact laser bench. Optics
on the same bench combine a pulse from each laser to pass through a
single KTP frequency doubling crystal, creating two 532 nm pulses
with nearly identical energy, beam uniformity and polarization.
Dichroic mirrors then remove the undoubled residual beams.
Separation times between the pulses may vary over a wide range, from
40 ns up to 100 ms. Minilite PIV lasers maintain long-term energy and
excellent beam pointing stability.
Beam quality
PIV requires that the dual pulses have the same spatial overlap, energy
and symmetry. Each PIV system leaves the factory with each laser
pulse matched in energy and beam quality. Extensive long-term
stability testing ensures that performance remains optimized.
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Stability
A solid mechanical design is the key to the Minilite PIV’s stability and
overall reliability. A decoupled Invar mount holds each resonator
securely, isolated from thermal and mechanical stress.
Ease of use
All PIV systems feature two digitally controlled power supplies, which
gives push-button access to all system parameters. Timing outputs
synchronize PIV pulses to other events. Independent power supplies for
each laser provide easy control of the PIV system, and the TTL
interface allow flexible external control.
Safety
Safety interlocks continually check for proper cooling water flow and
temperature.
Lifetime
Minilite PIV systems run at low output power levels. Reduced power
operation means longer lifetime for key components: rods, lamps and
power supplies last longer because of reduced stress.
Figure 8.1
Minilite PIV dimensions
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C. PIV optical description
Figure 8.2 shows the Minilite PIV optical layout. Two 1064 nm
fundamental Nd:YAG laser beams are first superimposed on a common
optical axis, passing through a single dounbling crystal. 532 nm
dichroics then separate the two green output pulses from residual 1064
nm light.
The beam from laser A defines this common optical axis. Horizontally
polarized, it passes directly through the beam merger, a dielectric
polarizer (4), which combines this beam with the second laser’s output.
Figure 8.2
Minilite PIV optical layout
Laser A
1. Rear Mirror
2. Pockels Cell
3. Wave Plate
4. Polarizer
5. Rod
6. Output Coupler
7. IR Mirror
8. Second Harmonic Generator
9. Window
10. 532 nm Mirrors
11. Optional Lens
12. Beam Dump
Laser B
Half waveplate (3) gives the fundamental output of laser B vertical
polarization so that the dielectric polarizer (4) superimposes the beam
into the horizontally polarized beam path. Mirrors (7) optimize this
overlap. The quarter waveplate (3) then gives both beams circular
polarization. Because they now have the same polarization, the
doubling crystal (8) converts them equally to the second harmonic. A
pair of dichroics (10) now removes the unconverted 1064 nm and steers
the 532 nm vertically polarized output beam.
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D. PIV operation
Startup
1. Place a power meter in the output beam and open the exit
shutter.
WARNING!
Be sure to wear goggles and observe all safety
procedures. Read the detailed safety instructions in the
front of this manual and follow them.
2. Set both lasers’ FLASHLAMP and Q-SWITCH switches
(Chapter II) to INT.
3. Turn on both lasers and allow them to warm up for at
least five minutes at 10 Hz or the desired final repetition
rate. Follow the Startup instructions in Chapter III.
4. Check each beam’s energy separately. If both beams’
energy are similar but low, perform the Maximizing
harmonic power procedure in Chapter III.
5. Place a target 3-5 m from the PIV and check beam
overlap by firing the lasers individually. Perform Beam
overlap (next page) if needed.
6. Turn both lasers to EXT mode (either FLASHLAMP or
Q-SWITCH or both), depending on whether you are
providing external TTL signal to fire the flashlamps, open
the Q-switches, or both (see this chapter).
7. Begin sending the external pulse sequences to both lasers.
8. Check both beam energies again and perform the Beam
power balance procedure if desired (next page).
9. Check the time between the laser pulses and adjust if
desired.
10. Begin PIV operation.
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Shutdown
1. Turn off both lasers and close the output shutter; refer to
Chapter III.
2. Turn off the timing pulse generator.
E. Dual beam overlap and power balancing
Adjustable optics
Laser B beam steering mirrors (2) and (3), and output steering dichroics
(7) and (8) all use the same mounts. Each mount has vertical and
horizontal adjustments (see Figure 3.4).
Note:
It is unnecessary and undesirable to move the
waveplates (1, 5), the dielectric polarizer (4) or the
beam A steering dichroics (9,10) for any reason.
Beam overlap
Beam alignment involves steering optics (2), (3), (7) and (8) only.
1. Warm up both lasers ~5 minutes and switch both to LOW
power.
2. Fire laser A at 10-15 Hz and set laser B to single shot
operation.
3. Center a 1 mm pinhole on the beams ~20 mm in front of
the PIV and set a target at least 3 m from the laser.
4. Steer the green laser A beam to the PIV target with
dichroic (7) while keeping the beam centered on the
pinhole with (8).
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5. Set laser A to single-shot mode, fire laser B at 10-15 Hz,
and steer the laser B beam to the target with dichroic (3)
while keeping the beam centered on the pinhole with
dichroic (2).
6. Turn both lasers off and remove the target and pinhole.
Beam power balance
PIV requires that both laser pulses have the same energy. Beam energy
is a function of the time interval between flashlamp firing and Q-switch
opening (“Q-switch delay”).
F. PIV pulse timing
The External Control section (Chapter III) describes fully how to
control flashlamp firing and Q-switch opening of a Minilite with TTL
signals. For PIV operation, you must control two Minilites
simultaneously. There are several strategies to follow, using either
external TTL signals and/or internal laser system signals. Remember
that the PIV’s internal signals have jitter of 1-2 µsec, while your TTL
signals can easily be accurate to ±1 nsec.
Note:
Remember that for external TTL signals to control
a flashlamp or Q-switch, its corresponding
INT/EXT switch must be on EXT. TTL signals are
0 to +5 Vdc, 10-20 µsec wide pulses.
Total flexibility
For maximum flexibility, you may supply four separate TTL signals,
firing both flashlamps and opening both Q-switches independently.
This method allows complete control of both Q-switch delays for more
ways of balancing pulse energies. In addition, this method allows
separating the PIV pulses by an arbitrarily long time. To use this
method, all four INT/EXT switches must be in the EXT position.
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Simultaneous flashlamps
If you wish, you may use a “Y” shaped BNC cable to send one TTL
signal to fire both flashlamps. This requires three TTL signals for
timing; one for both flashlamps and two more for the Q-switches. Now,
balancing beam energies and choosing beam delays are interdependent,
with adjustments become more difficult with larger pulse separations
(>20 µsec). For short separation times, this method is as flexible as
separate control of both flashlamps. Again, all four switches must be
set to EXT.
Internal flashlamp control
With a flashlamp switch in the INT position and its corresponding Qswitch setting on EXT, the flashlamp will fire at the selected repetition
rate. You may allow one flashlamp to fire at its normal repetition rate,
using its FLASHLAMP SYNC OUT signal to fire the other flashlamp
and synchronize the Q-switch control signals you generate.
Internal control
To eliminate the need for any external TTL signals, you may keep one
flashlamp in INT and use its FLASHLAMP SYNC OUT signal to fire
the other flashlamp (in its EXT mode) at the same time. By using both
lasers’ Q-switch delay adjustment pot (see Figure 2.1 and “Q-switch
delay lowers power” in Chapter III), you may choose different Qswitch opening times. This method will have high jitter (1-2 µsec), and
will also affect pulse energies. It may be a convenient method when
pulse separations are <20 µsec and a few µsec of jitter are acceptable.
Maintaining PIV optics
Periodically inspect the crystal and surfaces of all PIV optical
components for dust, discoloration, and damage. Cleaning or replacing
them, if necessary, will promote good system performance and longer
lifetime. See Optical maintenance in Chapter IV for details.
Note:
When cleaning the dielectric polarizer or a
waveplate, only clean the center of the optic. If
solvent reaches the edge of the optic, it may
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dissolve mounting glue, contaminating the optic.
Do not apply pressure during cleaning, for these
optics are thin and delicate.
Replacing the SHG crystal
The SHG (doubling) crystal is sealed in its mount, and damage to a
crystal face can be seen through the windows. If damage is visible (see
Inspecting and dusting optics, Chapter IV), Continuum recommends
returning the entire assembly for repair. To replace the crystal
assembly:
1. Turn both lasers off and bolt the new crystal mount
(Figure 3.4) into position. With either laser firing in LOW
mode, center the beam on the input window (5). Use an
IR viewing card to see this beam.
2. Center the beam in the exit window by rotating the
mount; use a business card to see the green beam.
3. Recheck the input window alignment and tighten the
mount.
4. Phase match the crystal (see Maximize harmonic energy,
Chapter III).
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Table 8.1 PIV Optical Parts
Item #
P/N
Description
Use
1
108-0004
½ plate
Vertically polarizes beam B
2
105-0199
1064 nm dichroic, 45°
Steer beam B onto beam combiner
(4)
3
199-0235
1064 nm dichroic, 90°
4
199-0131
Dielectric polarizer
Combines beam A&B
5
199-0004
½ plate
Circularly polarizes both beams
6
202-0174
SHG Crystal
Converts 1064 nm to 532 nm
7, 8
105-0200
532 nm dichroic
Steer 532 nm output beams
9, 10
105-0199
1064 nm dichroic, 45°
Steer beam B to beam combiner
11
640-1110
SHG assembly
Includes window (13), crystal (6),
waveplate (5) & adjustment mount
12
314-0277
Beam dump
Safety feature
13
110-0084
SHG exit window
Controls crystal humidity
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