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AdV-PSL (Pre-mode-cleaner block)
Cleva, Coulon, Genin, De rossi, Gosselin - 17:30 Wednesday 05 December 2018 (43914) Print this report
Offset at the slave and PMC error signal & neoVAN alignment

The primary goal of the shift was to invetigate the offset seen on the PMC error signal and the "weird" slave error signal (42906).

It turns out that the issues were related to some misalignment of the master beam in the crystal providing the 14 MHz for both slave and PMC systems.

It likely induces some RAM which features an offset at PMC and some efficiency reduction at the slave laser level.

- With a proper alignement we have raised the PDH of the slave from 1.4 V to 4 V pp. it seems also that we have noticeably increase the injection locking range which may have an impact on the IMC_OLTF. (data coming soon)

- the offset at the PMC error signal has disappeared and we have recovered a more "orthodox" shape.

--> this may impact the Freq-to-RIN coupling seen when we engage the SSFS: it couples SSFS features at the PMC_TRA

- we have checked that we are now able to reduce the Freq-to-RIN coupling with a dedicated offset on the error signal. ie with - 0,2 V offset wrt the PDH_pp = 2.5 V

- we have realigned the seeder vs the neoVAN, the power raise from 85 W to 94 W but with a larger pedestal

Seen at the PMC: the modal content (rough) is 79 %, the TEM02 is < 1,3 %

The power at the PMC_TRA = 62,9 W when we left (~ 17h00mn LT)

Comments to this report:
cleva - 12:03 Monday 10 December 2018 (43966) Print this report

After the adjustment of the beam upstream to the EOM providing the 14 MHz for both the slave laser end the PMC cavity we have noticed an increase of the PDH of the  

Upon arrival, the slave ramaputo is PSL_ELEC_9801_01
- PDH = 1.20 V pp
- F_mod = 14,53 MHz
- Att_RF = 14 dB (since 42866)
- Injection locking range is ~1 MHz
Rem.:  pay attention that V_PZT_monit is V_PZT/10 or /20, TBC later
-> see plot 1 & 2

# We find out that past issues related to PMC offset and Slave PDH size (42906) is connected to beam misalignment at EOM level.
Adjusting the Rmax mirror tilt upstream the EOM raised the slave from 1.4 V to 6 V pp !!
The injection locking range raises up to 3 MHz
-> see plot 3 & 4

New status now is
- PDH = 4.2 V pp
- Att_RF = 9 dB
- GF = 80 kHz
- lockable with an attenuation varying by 21 dB

-> see OLTF in plot 5

Conclusion_1:
- raising the PDH by a factor 4.3 means the power of the ML coupled into the salve has raided by 18
- raising the injection range by a factor 3,12 means the power of the ML coupled into the salve has raided by 10

It means the power of the ML coupled into the slave laser has raised by a factor 10-20!
* This can't not be reasonably explained by a feature of the EOM
(we have proceeded with a visual inspection to check for possible large misalignement on the crystals themselves)
* a guess is a possible dust somewhere on the path between the EOM and the slave which could clip 90 % of the ML power
--> to be checked ASAP


 

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genin - 14:57 Monday 10 December 2018 (43969) Print this report
90% of light lost seems a bit too much for a dust. We noticed as reported in https://logbook.virgo-gw.eu/virgo/?r=43945 that the power increase looks to be of the order of 5% if we trust the monitoring PD (PSL_ML_DC). I would assume that the rest was mainly due to misalignment of the ML with respect to the SL.
cleva - 22:27 Monday 10 December 2018 (43979) Print this report

To help undersstanding the IMC OLTF features (43923) we compare the OLTF of the injection lock of the slave laser with what got in 2007

plot 1 shows the OLTF of the injection lock of the slave laser with respect with what got in 2007.

- The amplitude are similar.

- The phase shows  25 ° difference at 100 kHz among the two meas.To be check whether this is a real phase change of something connected to the rrampauto (cosmetic filtering of the Error signal ports

 

No conclusion so far

 

 

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cleva - 9:12 Tuesday 18 December 2018 (44113) Print this report

We adjust the seeder alignement with respect to the neoVAN, we got:

• neoVAN modal content ~ 79 % (log # 43914)
• TEM02 < 1,3 %
• PMC_TRA = 62,9 W
• We mostly recover the power lost during the misalignment accident (6 W,  # 42256, #42148, 17/07/18 ) and the work around the neoVAN fiber( 2 W,# 42669, 11/09/18)

Rem.:

during ER13 it has been noticed some power reduction(~ 4% ) at the PMC_TRA (#44093) which is likely due to some beam drift at the PMC input

See plot

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cleva - 16:44 Friday 04 January 2019 (44245) Print this report

On the 10th of December we check also the compliancy of the Slave rampauto spare: ELEC_1811_01.

plot1 shows the error signals of the currently used rampauto ELEC_9801_01 (*) in July 2007 and in 5/12/2018.

plot1 shows also the error signals the "spare" ramaputo: ELEC_1811_01 on the 5/12/2018.

(*) ELEC_9801_01 is used since the very begining of Virgo

The ELEC_1811_01 (spare) increases the structure at 50-60 kHz which are supposedly due to the cross between the slow and fast piezo. This has to be confirmed and tuned if appropriate.

The structures are also present with the current rampauto ELEC_9801_01, in a more prominent way today wrt 2007. Could it be connected to piezo ageeing?

 

Next step:

- nothing specific is foreseen regarding the ELEC_9801_01

- a visual check that the ELEC_1811_01 is indeed a true copy of ELEC_9801_01

 

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cleva - 15:56 Thursday 07 February 2019 (44788) Print this report

please read

"...

New status now is
- PDH = 4.2 V pp
- Att_RF = 15 dB
- GF = 80 kHz
- lockable with an attenuation varying by 21 dB ... "

cleva - 15:25 Tuesday 19 February 2019 (44926) Print this report

- V_PZT_Monit is indeed 1/20 V_PZT

it means the calibration of the slow piezo mentionned on plot 1 is 46 MHz/V instead

- please replace plot 2 with the attced plot (gives the foreseen zoom)

 

 

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