Standard Operating Procedure
Lumonics 500 Excimer Laser

 

Excimer Laser

Introduction

This Standard Operating procedure applies to the Lumonics 500 excimer laser housed in Niagara College's High Power Laser Lab (V12). This class-IV laser currently operates with a mixture of helium and nitrogen gases and lase on two lines in the UV and violet region of the spectrum.

Statistics

Manufacturer: Lumonics, Inc.
Type: Excimer
Class: IV
Maximum Rated Energy: 6 Joules (pulsed)
Wavelength Range (in current configuration): 337nm to 428nm
Cooling: Flowing Water, 1 gpm
Power Source: Single-Phase, 120V, 20A per phase

Operating Procedure

Revised 2004/02/05 by M. Csele

STARTING the laser

  1. Don safety glasses suitable for the species being used. If using the UV molecular nitrogen species these glasses must have an OD of at least 3 at 337.1nm.
  2. Turn the cooling water supply ON. The valve is located near the front of the laser. Verify water flow if required by observing the output line to the drain.
  3. If not already on, turn the supply breaker (in the black panel) ON.
  4. Turn the POWER key on the laser control. The INTERLOCK OPEN light show be off and the WARM-UP INCOMPLETE light will illuminate. This warm-up time is required to preheat the thyratron in the unit. If the INTERLOCK OPEN light illuminates it may indicate a problem with water flow, a cabinet door open, or with the external room interlock (e.g. door switch).
  5. When ready, the HIGH VOLTAGE OFF button will light indicating a READY condition.
  6. Set the TRIGGER MODE to SINGLE SHOT
  7. Assuming the laser is pressurized with an appropriate gas mixture the HIGH VOLTAGE ON button may be pressed to energize the laser.
  8. Set the HV CONTROL as appropriate for the gas mixture in use
  9. Depending on the experiment, the TRIGGER MODE may be set to INTERNAL RATE (for repetitive pulsing), EXTERNAL (where an external experiment commands the laser to fire), or SINGLE SHOT in which the laser fires when the pushbutton is pressed.

High Voltage Controls
Figure 1: High Voltge and Firing Controls

SHUTDOWN

  1. Depress the HIGH VOLTAGE OFF pushbutton. Lasing will cease immediately.
  2. Wait 30 seconds for latent heat in the laser to be dissipated by the cooling water system
  3. Turn the POWER key OFF to remove power from the laser
  4. Turn the water OFF

GAS PURGE and FILL

    Evacuating the manifold of residual gases ...
  1. Close all four manifold SUPPLY valves
  2. Set the HALOGEN INJECT valve to the INJECT HALOGEN position
  3. Start the vacuum pump under the unit
  4. Set the MANIFOLD valve to the FILL LASER HEAD position
  5. Open the VENT valve from the laser head to release pressure in the head
  6. Close the VENT valve
  7. Set the MANIFOLD valve to the PUMP OUT GAS LINES position
  8. After 30 seconds, set the MANIFOLD valve to ISOLATE
  9. Set the HALOGEN INJECT valve to the ISOLATE position
  10. Evacuating the laser head ...
  11. Set the EVACUATE valve to the PUMP OUT LASER HEAD position
  12. Open the GAUGE valve to the READ VACUUM position
  13. Monitor the head pressure until it falls to the minimum value
  14. Close the EVACUATE valve
  15. Filling the head with active lasing gas ...
  16. Ensure all four SUPPLY valves are off
  17. Set the MANIFOLD valve to the FILL LASER HEAD position
  18. If not already open, Open the main valves on each large supply cylinder behind the laser
  19. Set the HALOGEN INJECT valve to the FILL BUFFER VOLUME position
  20. Set the HALOGEN INJECT valve to the FILL LASER HEAD position
  21. The amount of gas injected can be read on the VACUUM gauge by taking readings before and after this gas in injected
  22. Filling the head with buffer gas ...
  23. Close the GAUGE valve (ISOLATE VACUUM GAUGE position) to protect it from high pressures
  24. Open the BUFFER gas SUPPLY valve until the pressure gauge indicates that the head is pressurized to the desired level
  25. The laser is now ready to operate

Gas Manifold Controls
Figure 2: Gas Fill Valves

HALOGEN INJECTOR

Active lasing gas (halogen in an excimer, nitrogen in our case) is injected into the laser head in a controlled manner by adding it via a 'boost bottle': a small volume which holds a known amount of gas. The bottle is filled with the active lasing gas via the halogen inject valve and the charge of gas released into the laser head by switching the same valve to the 'inject' position. Figure 3 illustrates the operation of the halogen inject valve in the laser.

Before use, the amount of 'boost' added by this bottle must be determined. To do this, evacuate the laser head ensuring the vacuum gauge is open and reading close to zero. Seal the laser head from the vacuum pump, fill the boost bottle with nitrogen gas from the supply (at about 50 psi), note the pressure 'before' boost in the laser head and inject the boost gas. Note the pressure increase. Do this several times and average the increase in pressure. One may now calculate the concentration of lasing gas in the mixture by filling the evacuated laser to the required buffer pressure with helium gas. Convert this pressure to torr (15 psi = 760 torr = one atmosphere). Knowing that each boost bottle increases the pressure by a fixed amount the concentration of active lasing gas may be determined as a function of number of boost bottles 'dumped' into the laser head.

Halogen Injector
Figure 3: Halogen Inject Bottle Operation

Copyright (C) Niagara College, Canada, 2003-2004
This page is part of the PHTN1430 Course Page