(Michael R., Rick S., Oliver P.)

We turned the high power stage on to investigate, how the changed water fittings change the flow through the HPO components and therefore the laser performance. The current flow rates were already set similar to the ones right after the installation of the laser (in brackets): laserheads 0.6 lpm (0.6), frontend 1.5 lpm (1.5), powermeter 2.0 lpm (1.5), total xtal chiller flow 17 lpm (16.3). After minor tweaking of the pump currents and diode temperatures, 190 W outside the laser box could be recovered. initial settings:

DB1: 51 A; Db2: 48.7 A; DB3: 48.9 A; DB4: 49.2 A; output power: 182W (measured outside the HPO box with powermeter)

after changes: DB1: 50.9 A; DB2: 49.2 A; DB3: 50.4 A; DB4: 49.2 A; output power: 209 W at the internal shutter and 190 W outside (was: 190 W outside after installation).

We adjusted the phase between LO and EOM for the injection locking error signal at the delay box.

initial diode temperatures (in deg. C):

DB1:

D1: 25
D2: 25
D3: 27.5
D4: 23
D5: 27.5
D6: 25.5
D7: 23.5
(remained unchanged)

DB2:

D1: 22
D2: 23
D3: 24.5
D4: 22
D5: 22
D6: 22.5
D7: 22
(increased all temps by 1 degree C for DB2)

DB3:

D1: 22.5
D2: 26.5
D3: 26.5
D4: 23.5
D5: 26.5 to 27.5
D6: 21.5 to 22
D7: 24.5 to 23

DB4:

D1: 23
D2: 20.5
D3: 22
D4: 20.5
D5: 22.5
D6: 22.5
D7: 22.5
(increased all temp by 1 deg C)

A quick DBB scan without any alignment showed a higher order mode content of 8.3 %.

We decided to neither remove the water filters as in Livingston, nor put an HR mirror next to the output coupler in order to create an intermediate power system from 100 % reflection of the Frontend.

We used the attenuation unit next to the output of the laser box to send up to 50 W to the PMC path. The modematching lenses had been shifted to their marked positions for high power operation and the power levels on the PMC locking photodiode and the ISS photodiodes had been set to the values, mentioned in the instructions. The FSS-path had been blocked. We locked the PMC and optimized the alignment (mirror setupstream the PMC, gain and offset of the control loop), and measured little less than 10 % in reflection of the PMC.

The ISS had been locked.The most stable configuration for this had been found with a gain of about 10 dB. The refracted power at the high power AOM was around 6 %. However, the ISS fell out of lock from time to time - apparently, the settings for the control loop has to be optimized.