JasonO, PeterK, RickS
This morning both Peter and Jason carefully inspected the crystals inside the 35-W amplifier both with and without pump light (Peter also with the amplifier seeded and operating nominally). There were some indications of slight contamination, but no clear evidence of damage or a broken crystal.
This morning, we also found that the 35-W laser from the 3rd ifo. storage (Spare1-1208-7) had an NPRO inside the box that was not placed in the nominal location, i.e. not aligned.
We suspected that the unit that was in the H1 Diode Room (OB2-1207), which had an NPRO inside that was mounted in the nominal location, was aligned. We found this not to be the case after energizing the NPRO and inspecting the beam path. The output beam was clipping on the EOM aperture.
So we divided into two efforts. Jason and Rick working on aligning the NPRO beam through the OB2-1207 MOPA, and Peter working on trying to improve beam quality, while maintaining input power, in the 35-W laser (OBS3-0909) that is currently installed in the H1 PSL (the one with the suspected damage in the 35-W amplifier).
We have completed the alignment of the NPRO beam in OB2-1207, with the following power levels (measured using the small, 10-W thermal head):
- Upstream of EOM: 2.202 W
- Downstream of EOM: 2.161 W
- Downstream of AOM: 2.142 W
- Upstream of last turning mirror before the 35-W amplifier (between M4 and M5): 2.031 W
Peter's alignment of OBS3-0909 is showing some promise. Adjusting the alignment into the amplifier and the alignment of the pump light into the 4th crystal, the beam quality was significantly improved - as good as it has been in a long time. At 47 amps to all pump diodes, the output power is about 33 W. This effort will continue in the morning.
Details will be appended to the aLog entry.
The crystal faces of the front end amplifier were inspected. No obvious signs of damage were found by me. What I suspected might have been a fracture in the crystal for head 1 is most likely, in retrospect, a reflection of the bottom edge of the crystal onto the gold coated cooling mount as seen through the front face of the crystal. Nothing untoward was noticed about the pump light distribution. The amplifier output window had a small hazy spot on it. The output window of the front end laser housing had some particles that were drag wiped off. Attached are images of the pump light spot on the amplifier housing. Although the image for head 1 (P1.jpg) might suggest that the pump light is clipped that is only because of the placement of the mirror mount that turns the beam from the NPRO. The pump light incident onto the crystal is not clipped.For 35-W "Front End" laser Spare1-1208-7:
133.5 lbs
30” x 30” x 8.5” without handles
Handles add 1.5” to height
For context, attached are a few photos of the internal components of the amplifier in the 35-W "Front End" MOPA (master oscillator power amplifier) laser.