Thursday, August 3: Bruce started system around 7 AM this morning with REAL LabVIEW program version 3.0 running for first time. Shane arrived around noon. Flow from south with gust structures in scans and cumulus clouds.
At 21:02 UTC today, the power cable to the Nd:YAG laser power cable connector was accidentally struck by the transmitter enclosure side wall while closing it. (The enclosure side wall was opened briefly to inspect the pressure transducer on the Raman cell.) The slip joint hinges that allow removal of the side wall for transmitter maintenance also make it possible to lower the wall in the incorrect lateral position and strike the cable connectors on the back of the Nd:YAG laser. Even though the Nd:YAG is firmly bolted to the optics table, striking the cable apparently shifted the pointing of the 1064 nm wavelength pump beam ever so slightly. We observed a deteriorating transmit power in the minutes after the strike and shut the system down at 21:28 UTC.
A subsequent inspection of transmitter optics led to the discovery of a damaged mirror downstream of the Raman cell. It is the first mirror downstream of the Raman cell installed in a large gimbal mount. This mirror is particularly vulnerable since the Nd:YAG beam has the smallest diameter and high fluence there. It is not known whether the damage had taken place as a result of the strike, or whether it resulted from a prior incident. The 2" diameter mirror was removed, cleaned, and rotated 180 so that the damaged spot was out of the way. The mirror specs are: 2" diameter, 1/2" thick, front surface: HR dichroic at 1543 nm and AR at 1064, back surface AR coated at 1064. All coatings for 45-deg AOI. This is a custom mirror and we do not have 2" spares. It appears we have numerous 1" spares. We ordered a 2" to 1" adapter in case we need to use the 1" versions in the future. But the 2" mirrors are much easier to use in this position because the design is to let the bulk of the Nd:YAG energy pass through the mirror at this stage.
We also noted the 1543 injection seed beam profile was bright and fine suggesting that the other optics were not damaged. We then used the gimbal upstream of the Raman cell to steer the Nd:YAG pump beam to completely overlap the injection seed. This was a very small adjustment (like 1/4 turn on micrometers). At 22:49 UTC we restarted the system. We operated the system until 6:15 PM and shut it down for the night.
The photo below shows the side wall to the transmitter enclosure and the cables to the Nd:YAG laser.
The photo below shows the damaged mirror in the gimbal mount after rotating it 180-degrees.
Riddle: Striking the Nd:YAG cable also caused a step-function-like decrease in the 1064 nm pump power as shown below a little after 21:00 UTC. No optical elements were adjusted to restore the aiming of the pump beam on the energy monitor. Yet, the pulse energies were higher when we restarted the system.
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Unknown User (shane)
Thursday, August 3: Bruce started system around 7 AM this morning with REAL LabVIEW program version 3.0 running for first time. Shane arrived around noon. Flow from south with gust structures in scans and cumulus clouds.
At 21:02 UTC today, the power cable to the Nd:YAG laser power cable connector was accidentally struck by the transmitter enclosure side wall while closing it. (The enclosure side wall was opened briefly to inspect the pressure transducer on the Raman cell.) The slip joint hinges that allow removal of the side wall for transmitter maintenance also make it possible to lower the wall in the incorrect lateral position and strike the cable connectors on the back of the Nd:YAG laser. Even though the Nd:YAG is firmly bolted to the optics table, striking the cable apparently shifted the pointing of the 1064 nm wavelength pump beam ever so slightly. We observed a deteriorating transmit power in the minutes after the strike and shut the system down at 21:28 UTC.
A subsequent inspection of transmitter optics led to the discovery of a damaged mirror downstream of the Raman cell. It is the first mirror downstream of the Raman cell installed in a large gimbal mount. This mirror is particularly vulnerable since the Nd:YAG beam has the smallest diameter and high fluence there. It is not known whether the damage had taken place as a result of the strike, or whether it resulted from a prior incident. The 2" diameter mirror was removed, cleaned, and rotated 180 so that the damaged spot was out of the way. The mirror specs are: 2" diameter, 1/2" thick, front surface: HR dichroic at 1543 nm and AR at 1064, back surface AR coated at 1064. All coatings for 45-deg AOI. This is a custom mirror and we do not have 2" spares. It appears we have numerous 1" spares. We ordered a 2" to 1" adapter in case we need to use the 1" versions in the future. But the 2" mirrors are much easier to use in this position because the design is to let the bulk of the Nd:YAG energy pass through the mirror at this stage.
We also noted the 1543 injection seed beam profile was bright and fine suggesting that the other optics were not damaged. We then used the gimbal upstream of the Raman cell to steer the Nd:YAG pump beam to completely overlap the injection seed. This was a very small adjustment (like 1/4 turn on micrometers). At 22:49 UTC we restarted the system. We operated the system until 6:15 PM and shut it down for the night.
The photo below shows the side wall to the transmitter enclosure and the cables to the Nd:YAG laser.
The photo below shows the damaged mirror in the gimbal mount after rotating it 180-degrees.
Riddle: Striking the Nd:YAG cable also caused a step-function-like decrease in the 1064 nm pump power as shown below a little after 21:00 UTC. No optical elements were adjusted to restore the aiming of the pump beam on the energy monitor. Yet, the pulse energies were higher when we restarted the system.