Standard Operating Procedure
Apollo/Polaris 22HD Double-Pulse Ruby Laser

Ruby Laser Firing - Oscillator and Amplifier Rods
This laser, a solid-state ruby laser, sports a fast E-O modulator allowing production of multiple pulses for holographic use. The laser is configured as a MOPA system using two rods: an oscillator (seen here in the yellow housing to the left) and a larger amplifier (in the housing to the right). Also visible in this photo is the E-O modulator to the far left and the Etalon OC.

Last Updated 2011/05/17

Introduction

This Standard Operating procedure applies to the Apollo/Polaris 22HD ruby laser housed in Niagara College's Advanced Optics Lab (V13A). This class-IV laser has a visible output in the red and is used primarily for holographic applications.

For a summary of Operating Procedures, Click Here. Because of the unique, and complex, nature of this laser, this SOP contains a general description of the controls as well as the timing system.

Statistics

Manufacturer: Polaris Research Group
Model Number: 22HD
Type: Ruby
Class: IV
Wavelength: 694 nm
Maximum Rated Energy: 3 Joules per pulse, 1 Joule typical
Pulse Width: 30ns to 50ns nominally
Number of Pulses: 2
Pulse Separation: 1us to 500us
Cooling: Closed, deionized, water-cooling loop with attached chiller
Power Source: Single-Phase, 120V and 220V (chiller)
Coherence length: 2m to 10m
Jitter: +/- 10ns

Oscillator Rod Specifications from the test report from Saint-Gobain Crystals dated 6-19-01:
Serial # A20K, Boule # 22-3302-06
Size: 3.020" * 0.3756"
Doping: 0.05% +/- 0.005% Cr
Coatings: A/R coated (694nm) on both faces (0.18% measured R at each face)

For EO Modulator specifications, Click Here

Hazard Analysis

Report ID: 100531154730
Performed On: 2010/05/31
by Laser Safety Officer: D. Turnbull
Input Data: 694nm, Single Pulse, 1.0J, 3E-08s pulse duration
Beam Diameter: 8mm
Small Source Ocular MPE: 5.0E-07J/cm2

Worst Case Optical Density: 6.72 OD
Intrabeam Eye NOHD: 1.07+04m
Small Source Eye Diffused Reflection NHZ: 3.8m
OD for Diffused Observation Range 1.46OD


System Components

Ruby Laser Components

All components are mounted on a large optical rail. The photograph below correlates each component on the diagram above to the actual component as seen with the cover removed.
Ruby Laser Components


System Controls

Excepts from the Operations and Service Manual. Updated 2010/05 to reflect new controller functions (Logic controller replaced).

Ruby Laser Control Panel

System Electronics Operations Summary

Excepts from the Operations and Service Manual

The following oscilloscope output, captured using a high-speed silicon photodetector on the laser output, shows typical timing of a single Q-switched laser pulse. At t=0 the laser is fired and the oscilloscope triggered ... the trigger point is 200μs to the left of the screen and so is not seen here. In this case the OSC LAMP delay setting is 350μs and a spike appears when the lamp fires (electrical noise generated by the ignition process). Similarly, the AMPLIFIER lamp fires at 600μs. The baseline is seen to rise gradually at this point from (amplifier) pump light which leaks from the amplifier housing (scattering from the rod) striking the detector. The Q-switch delay is set for 900μs which is where the first laser pulse appears - if the Q-switch voltage is set properly. The laser pulse does not occur here - only the electrical 'spike' caused by the pulse generator. The fact that the 'spike' is not actually laser output can be verified by the fact that the height is proportional to the applied Q-switch voltage throughout the entire range! The second laser pulse (QS2) is fixed in time and occurs at 1000μs with the spike seen here.

Ruby Laser - Q-Switched Laser Output

In the lower photo, the trace is re-adjusted so that the trigger point is 100μs to the left. Pulse #1 is not firing here (the thyratron misfired in this example) and pulse #2 is seen to produce lasing - evident here by the fact that the optical output not only 'spiked' (the width of the laser pulse is about 50ns and the horizontal scale is 100μs per division so the laser output appears as a 'spike' in the figure), but the detector also saturated with the intense energy of the pulse.

Ruby Laser - Q-Switched Laser Output

Conventional (Burst) Operation

Pulse-On Q-Switch Operation

Double-Pulsed Operation


Manufacturer's Test and Parameter Data

Excepts from the Operations and Service Manual

Double Pulse Settings #1 typical settings for equal-pulse operation
Double Pulse Settings #2 control panel settings
Output vs. Oscillator Delay indicating optimal delay for oscillator lamp
Output vs. Amplifier Delay indicating optimal delay for the amplifier lamp
Output vs. Q-Switch Voltage indicating hos Q-switch voltage (via the thumbwheel) affects power output
Amplifier Gain showing how the amplifier depends on capacitor voltage


Pockels Cell Data

Excepts from the inspection report from Cleveland Crystals, Inc. (Evaluated 1-12-01)

Type: QX1020, Serial # 9214

Halfwave Voltage at User Wavelength (λuser):
V1/2 - User = V1/2 - 633 nm * (λuser / 633nm)


Operating Procedure

Revised 2011/05/17 by M. Csele

Preparing the water cooling system:

When the system has been sitting for a period of time, stagnant water in the system becomes contaminated and conductivity of the cooling water becomes low. Each time before running the system the water cooling system must be purged and refilled with fresh deionized water.
  1. Remove the Haake C-10 circulator (by lifting it) in order to observe the coolant level in the tank
  2. Ruby Laser Coolant Level Ruby Laser Coolant Circulator/Heater
    The coolant level can be easily observed through the opening for the circulator. Ensure the unit is OFF before removing it from the unit as seen to the left. To the right, the circulator is installed.

  3. Open the DRAIN valve (ORANGE handle) beside the chiller to the right
  4. Turn the HX-75 chiller ON. The chiller will begin draining
  5. When air bubbles appear in the coolant lines (and the coolant level is at the bottom of the tank), turn the chiller OFF
  6. Close the DRAIN valve (ORANGE handle)
  7. Open the FILL valve (BLUE handle) on the wall behind the chiller. The chiller will begin filling from the microelectronics DI water supply
  8. When the chiller tank has filled within 5cm of the top (as seen through the circulator hole on the top of the chiller unit), close the FILL valve (BLUE handle)
  9. Turn the HX-75 chiller ON and allow coolant to circulate through the laser
  10. Re-install the Haake C-10 circulator/heater unit into the tank (the entire bottom of the unit including the pump and heating coils must be immersed)
  11. Turn the street water cooling loop flow ON via the quarter-turn valve on the rear wall and adjust water flow to a low rate (about 1 litre per minute) by observing the out flow
  12. Turn the Haake C-10 circulator ON, set for 21 degrees C, and allow the water to heat until the yellow HEAT ON indicator oscillates slowly indicating the coolant is at the proper temperature

STARTING the laser

  1. Don safety glasses suitable for use with a ruby laser (694.3nm).
  2. Chiller unit must be turned on (as per the above instructions) and coolant water circulated for 10 minutes minimum and settings must be per this manual (approximately room temperature) prior to any Laser operation. Cooling system integrity (i.e. no system leaks) must be verified prior to any Laser operation - ensure the WATER FLOW interlock indicator is extinguished.
  3. Turn on the power supply which must "warmup" after power-up for 10 minutes minimum in "dumped" condition prior to any Laser operation. If an interlock is open, it will be indicated on the front panel and the DUMP lamp will blink rapidly. Ensure all interlocks are closed.
  4. If the experiment requires it, turn the alignment HeNe laser on
  5. External optical components must NEVER have plane surfaces parallel to Laser rod ends (perpendicular to beam propagation vector). All plane surfaces must be set at some small angle off perpendicular to beam propagation direction vector to prevent back-reflections from propagating back into Laser rods and flashlamps.
  6. Complete optical cleanliness must be maintained at all times. Full power Laser pulses must propagate through external optical components without impediment. Any debris or dirt on optics (including Laser pulse induced) will cause severe damage to optics and/or Laser rods and flashlamps.
  7. Upon Power Up of chiller unit and power supply entire laser system must be checked for water leakage in laser housing, at water lines (internal and external), and in enclosure.
  8. Chiller must be filled with only DE-IONIZED water. Chiller water temperature setting In operation should be adjusted so that coolant temperature in laser system is approximately room temperature, i.e.: around 70 degrees F / 21 degrees C.

OPERATING the laser (summary)

  1. Setup the voltage and Q-Switch controls as per the instructions in this SOP (and as required by the experiment).
  2. Once the laser is ready, and after the ten minute preheat cycle, the MANUAL mode lamp will be lit and blinking slowly.
  3. Turn the SAFETY switch to ARMED ONLY when ready to fire the laser - turn it to SAFE immediately after use and when working near the front of the laser
  4. Press the CHARGE button to charge the capacitors. If the capacitors fail to reach full charge within ten seconds, an error will be indicated by blinking DUMP and FIRE lamps - seek technical assistance if this happens.
  5. Once charged, the FIRE lamp will illuminate. Press the button to fire the laser.
  6. After firing the laser, the DUMP lamp will illuminate (without the MANUAL lamp illuminated) and blink for approximately 45 seconds during which time charging is inhibited (this prevents rapid-firing the laser which will damage the lamps).
  7. When the MANUAL mode lamp lights again, the next charge/fire cycle may be initiated.
  8. When using the laser for holographic exposures it may be necessary to turn off the front-panel indicator lights using the small toggle switch in the center of the control panel. Normally, this switch is left in the UP position allowing the indicators to operate.

SHUTTING DOWN the laser

  1. Turn both the POWER and SAFETY keyswitches on the power supply
  2. Turn the Haake C-10 Circulator/Heater OFF
  3. Wait one full minute to allow the chiller to remove latent heat in the pump lamp chambers
  4. Close the street water cooling flow valve (quarter turn)
  5. Turn the HX-75 chiller OFF and the alignment HeNe laser OFF

Maintainence Information

Revised 2010/05/13 by M. Csele

Water Cooling System
The water cooling system must not incorporate any brass fittings - only stainless steel or plastic must be employed in the system. Main coolant lines are 'food safe' poly lines. The chiller has been modified with a lowered intake allowing almost complete draining of the reservoir tank. Tees bring DI water from the V13C (cleanroom) system into the system. A low-flow GEMS flowswitch (0.1 gpm min) is installed in the loop immediately beside the chiller. The flowswitch is powered from 24 VDC from two adapters and a simple contact closure indicates adequate water flow. Electrical connection is made to the laser power supply via a specially-keyed 5-pin DIN connector.

Plumbing inside the laser rail features two valves allowing the isolation of the amplifier from the rest of the coolant system. Should the experimenter desire, the amplifier rod could be substituted for the oscillator rod by isolating the coolant system and re-installing the amplifier housing where the oscillator normally resides.

Periodically the chiller reservoir must be cleaned thoroughly to remove particulate matter which accumulates.

Power Supply System
Interlocks were added to comply with CDRH and ANSI standards. As shipped, the unit featured only a single interlock loop for the power supply door and the rack. A single relay under the main chassis (lower left side) is used to indicate interlock status - the coil has a white/org and white/red wire. The white/red wire connects to the interlock switches which are in series (Green ground -> switches in series -> white/red relay coil). Unregulated Power is derived from the logic board (Drawing 100388) in slot J1. Additional interlocks are added on the (-) side of the relay coil as a series circuit incorporating the water flow sensor, two external inputs (one on the back of the power supply - intended for the room door interlock, one at the laser head - intended for a class-I interlocked experiment), and a cover interlock switch.

Relays
If the dump solenoid fails to pull-in, or pulls-in intermittently (this is often seen as a failure for capacitors to reach full charge), replace the PUMP relay (a Potter&Brumfield K10P-11D15-12 unit) under the HV chassis (pull the supply out of the cabinet half-way). This relay is socketed.

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