Written by: Robert Nicholas Ettelbrick 

The following procedure should be used if there are any concerns regarding the alignment of the Legend regen into the Legend compressor. This procedure is not a full compressor alignment procedure. It is an alignment check procedure that also provides details necessary to make minor adjustments to the compressor input/output beam.

Below is the photo showing the portion of the Legend bench that will need access to perform the compressor alignment check.

Compressor alignment check/adjustment procedure

Care must be taken when performing this procedure such that the beam propagating through the stretcher portion of the Legend bench is not partially blocked or interrupted in any way. Failure to adhere to this can result in serious optical damage to the regenerative amplifier. If there is any fear that the stretched beam may be interrupted, then take the steps necessary to operate the regen in the “unseeded, q-switched” mode described at a section that follows the section below, and then refer back to this section for the procedure.

  1. The LSS must be in Class 4/maintenance or Class 4 Split/maintenance mode
  2. Remove top-right cover on Legend. Defeat two interlocks and turn.
  3. Referring to the photo, locate the iris labeled as Comp1/Comp2 and insert them into the appropriate post holders.

  4. Turn on Evo at a pump level approx 1-1.5A less than normal operating current. This will effectively lower the regen output power to a safer level appropriate for viewing the regen/compressed beam on a white or orange card..
  5. Using a fluorescent orange card, carefully check the alignment of the regen beam through the iris’s before the compressor grating. Be sure not to bump or touch the grating while doing this, as the space for this test is extremely limited. Carefully close down a. Comp1 iris while observing the beam centering through the iris, then open and b. Do the same for Comp2 iris. If the regen beam appears uniformly clipped at both iris’s as they are partially closed around the beam, then the procedure is complete as no adjustment is necessary. 
  6. If the beam is not centered on both iris’s then adjustments to two routing mirrors that are located before the iris’s will be necessary. Referring to the photo, adjust mirror 1 x-y to center beam on Comp1 iris and then adjust mirror 2 x-y to center beam on Comp2 iris.

  7. After the beam has been well centered, remove both irises. The regen beam should be passing through the compressor and out of the Legend onto the optical table. It may be necessary to make very slight adjustments to Mirror 2 while viewing the beam as it passes through Ext iris 1 ( see photo below) located under the plexiglass cover following the Legend. It will be necessary to check and adjust Mirror 2 if the beam is not well centered through Ext iris 1. This check and adjustment will be necessary IF Mirror 1 and/or Mirror 2 have been adjusted for alignment through Comp1 and Comp2 iriss. 

  8. Turn off Evo laser, replace Legend top cover and turn Evo on to normal operating current.

Procedure for operating regen unseeded, q-switched/cavity dumped

If there are any concerns that the stretcher beam path will be interrupted or if there are any adjustments necessary to the compressor alignment OTHER than those adjustments described above ( Mirror 1 and/or Mirror 2), then it will be necessary to operate the regen in the safest possible mode, which is the unseeded, q-switched/cavity dumped mode. The procedure for this is as follows:

  1. Remove top-right cover on Legend. Defeat two interlocks and turn.
  2. Place a beam block between the stretcher output and the regen seed path input (a block before the last turning mirror for the seed beam before regen is a good location). 
  3. Adjust SDG delay 2 to a longer delay, approx 80 ns longer than normal operation. Be sure to note the original set delay before making this change.
  4. Turn on the Evo to a current level slightly less than normal level, appox ½ amp less. The appropriate current level will be when the scope trace looks like the photo below. The trace below shows the regenerative amplifier operating Q-switched in the absence of a seed pulse from the Vitara and also shows the regen “cavity -dumping” the q-switched pulse. 

Regen operation in this mode represents the safest mode of operation. All alignment procedures of compressor and optical path beyond the Legend can be performed in this mode as an alternative to operating the Legend in the normal seeded mode. When returning the Legend to the normal seeded operation, it will be necessary to:

  1. Unblock the seed beam from the regen input
  2. Return the SDG output 2 to the original delay value
  3. Return the Evo to the original current.


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