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AdV-PSL (Laser Bench setup)
gosselin, derossi - 16:30 Tuesday 02 March 2021 (50944) Print this report
ML temperature set point - Mode hop range

This morning we tuned the temperature of the crystal of the ML to bring it in a middle of a mode hop range (following log entry https://logbook.virgo-gw.eu/virgo/?r=50870)
The procedure to find the temperatures at which the mode hops appear is attached to this entry.

Here below are the temperature scans that we did.
Times are in local time.
Temperatures are taken on the display of the ML.

10:18  
scan SL ok
initial temperature of the ML 24.64

10:20 23.3
10:23 22.6

from 10:23 to 10:24
22.6 -> 23.0
PDH a bit dirty at 23

10:25 10:26
23 -> 24

10:26  10:26:20
24 -> 23.6
PDH dirty at 23.6

10:28
back to 24.6
we increase the temperature

10:29
24.6 -> 25.2
second pdh and first pdh still clean

10:30 25.8

10:31:30 to 10:32
25.8 to 26 back to only one pdh

We decrease the temperature

time?
25.8
The second PDH clearly appeared

10:35:30
25
second PDH disapear

We increase the temperature
a bit dirt from the beginning
25.5 2 PdH

We decrease the temperature
10:39:00
23.7 it starts to be a bit dirty

10:40:00
Kind of dirty while going down till 23 then starts to be clean again.  

Decreasing the temperature
10:41:00
22.5 two PDH, clearly  

10:43 to 10:44
down to 21.6
second pdh disappear but still a bit dirty
minimum of the ML

Increasing of the temperature

10:44:40
10:45 2 pdh molto chiaro
10:45 22.6 gradi, secondo sparito

keep on increasing the temperature
between 23.2 and 23.7 pdh a bit dirty

10:51:00
24
PDH is clean

keep on increasing the temperature
25.2 second PDH, clearly  

10:59 to 11:00:00
25.1 to 24.3
 
Conclusion:


While decreasing the temperature the mode hop appear at 22.5, while increasing the temperature mode hop appear at 25.2.
The temperature setpoint should then be 23.85.
However we observed that, without clear reasons, the PDH was a bit dirty between 23.2 and 23.7 (plot 1), so to keep it away from that range we set the temperature at 24.3 degrees.

Images attached to this report
Non-image files attached to this report
Comments to this report:
chaibi - 13:49 Wednesday 03 March 2021 (50966) Print this report
The PDH signal distortion looks like a hysteresis effect which depends on the T°. Hence, it shouldn't be an issue for the lock.
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