NAOJ GW Elog Logbook 3.2
Matteo, Simon
We tried to start recovering the absorption bench today by reactivating the translation-stage. For this step it is necessary to reset the position of the stage, but unfortunately we got problems with this especially for the vertical axis of the stage.
After some time of an unsuccessful try and error approach, we called Manuel and tried to redo the steps he was doing usually.
In the end, we could reactivate the whole stage by tricking the Zaber console (the PC program controlling the stage) which turned out to be the main burden for a proper reset since the predefined limits for the vertical axis made it impossible reach the "home" position manually.
Actually, I added a more particular description of what we have done in the GWPO wiki: here and here
By rough estimation, the reflected power dropped ~0.3mW, though I could not see any transmitted flash.
The reflected beam power was ~3mW with 3.5V.
The dip was ~0.4V.
3mW * 0.4V / 3.5V ~ 0.3mW
The loss and high reflectivity may cause too small transmitted power.
I updated the input optical layout as attached figure.
HOMs pahts are under construction now.
[Aritomi, Eleonora P&C, Yuhang]
This is work on July 5th.
We scanned green phase at 1kHz and scanned AOM again. The result of AOM scan and TEM00 are attached. With 1kHz green phase scan, TEM00 peak isn't measured properly. After AOM scan, we locked IR on TEM00 and HG01,10 and measured each power with dataviewer.
| AOM frequency (MHz) | IR transmission | mode |
| 109.03643 | 500 - 1200 | TEM00 |
| 109.43154 | 100 - 200 | HG10 |
| 109.43199 | 150 - 400 | HG01 |
Then we tried to improve the alignment of IR. TEM00 and HG10,01 with 10 Hz green phase scan after the alignment is as follows.
| AOM frequeny (MHz) | IR transmission | mode |
| 109.03646 | 100 - 5500 | TEM00 |
| 109.43156 | 100 - 300 | HG10 |
| 109.43204 | 100 - 400 | HG01 |
We haven't measured all the higer order modes, but mode matching should be around 90% now.
I measured the transmittance of one of the silicon mirrors using power meter.
When I injected 10mW power laser, the transmitted power was about 0.2uW.
This corresponds to T=20ppm.
If the loss is zero, this transmittance corresponds to finesse~150,000.
So it seemes that the coating is not what we wanted.
Yesterday, I measured the beam profile, and the beam had its waist around 1250mm distance from FI with ~60um beam radius.
Then I adjusted the beam height to achieve ''straight'' beam.
Next, I scaned the laser freq. using both temp. control and PZT of the laser.
During scanning the freq., I monitored both transmitted beam, and reflected beam.
I could see some dips in reflection, though I could not see any transmitted beam.
I have not checked the error signal yet, it may be possible to lock the laser, but it seemes difficult to see transmitted beam.
By rough estimation, the reflected power dropped ~0.3mW, though I could not see any transmitted flash.
The reflected beam power was ~3mW with 3.5V.
The dip was ~0.4V.
3mW * 0.4V / 3.5V ~ 0.3mW
The loss and high reflectivity may cause too small transmitted power.
[Aritomi, Eleonora P&C, Yuhang]
Today we tried to improve IR alignment into filter cavity.
First we increased green power to 68mW. OPO temperature is 7.2 kOhm and p pol PLL frequency is 150 MHz. IR injected into filter cavity is around 13mW. Then we locked IR on TEM00 and maximized TEM00 by aligning two steering mirrors for IR. During IR alignment, green transmission was above 5000.
Since lock of green phase is not stable, we scanned green phase with 10Hz and 1.3Vpp. Then we scanned AOM frequency at 2 mHz. After the scan, we locked IR on TEM00 and HG10,01 and measured each power with dataviewer. We repeated alignment of IR and AOM scan twice. Attached pictures show cavity scan. IR transmission when IR is locked on TEM00 and HG10,01 is as follows.
After scan 1
| AOM frequency (MHz) | IR transmission | mode |
| 109.036 | 100 - 2000 | TEM00 |
| 109.43 | 100 - 400 | HG10 |
After scan 2
| AOM frequency (MHz) | IR transmission | mode |
| 109.03646 | 100 - 3800 | TEM00 |
| 109.43133 | 100 - 270 | HG10 |
| 109.432 | 100 - 400 | HG01 |
This scan seems strange and is not compliant with measurement when IR is locked due to green phase scan. Pic 3 shows TEM00 in scan 2. Given that linewidth of filter cavity is 100Hz and AOM scan speed is 8kHz/s, frequency of green phase scan should be higher than 80Hz. Actually we tried 1kHz once, but TEM00 peak hight became smaller.
Anyway now TEM00 is 10 times larger than highest HOM. It seems that mode mismatch is small. We'll continue the alignment tomorrow.
This afternoon, Matteo checked my experimental setup, and gave me some advices.
Following his advice, I measured beam profile.
I will upload the results tomorrow...
Today, Aso-san pointed out that the silicon mirrors may have higher finesse than we expected.
Therefore, I checked the spec sheet of mirrors, and the designed reflectance is more than 99.997%, which corresponds to more than 100,000 finesse, though we ordered as 50,000 finesse.
The manufacturer may assume that the loss (probably ~30ppm) reduces the finesse from ~100,000 to 50,000.
However, it may be almost impossible to see transmitted beam with such high finesse and loss...
Today, I re-started the installation of optics for double-pass AOM which is used in HOMs paths.
The beam is aligned roughly.
In addition, I cleaned silicon mirrors using First Contact.
Then I installed them inside the chamber, but still cannot see any flash.
Also I re-designing the cavity in order to make another set of mirrors which have lower finesse and high coating quality.
Firstly after the new measurement of the mechanical transfer funtion of GRMC, the notch filter 2 was modified as below:
The center frequency of the notch filter was tune to 9,47kHz without changing the Q factor (1 as previously).
C60; C63; C61; C62; : 560 pF (unchanged)
R79; R80; R81; R82: 30 kOhm (instead of 24 kOhm previously)
We didn't succeed to lock the GRMC, so I checked completely the filter section of the servo: it appears after measurement of the transfer function of the 1/f filter, that the corner frequency was displaced from 2,2 kHz to 9 kHz.
It appears that the C38 capacitor was damaged. The C38 capacitor was replaced by a 33nF capacitor and the transfers function was restablished.
We always didn't succeed to lock the GRMC. It appears that the error signal in scan mode has an amplitude of -20mv / + 30mV which is weak for the current design of the servo. So the hysteresis of the detection comparator (U23 - LM311DR) was reduced drastically from 10mV to 0.5mV (largely less than the amplitude of the error signal in scan mode).
The R108 resistor was changed to a 10 MOhm resistor (instead of 470 Kohm previously).
After this modification, the GRMC locking was succesfull and robust.
We tuned the gain (position 3 of the gain potentiometer) in order to have a gain margin of 10dB (at phase 0 deg) and a unity gain frequency of 1.6kHz (more than 50 degree of phase margin).
So the GRMC servo is now functional and we can go on the modification of GRMC and MZ servos for synchronized locking.
Error signal is 30 mVpp and conversion factor from V to rad is pi/0.03 = 105 rad/V.
[Aritomi, Eleonora P&C, Yuhang]
This is work on July 2nd.
First we increased green power to 60mW. OPO temperature and p pol PLL are as follows
| green power (mW) | OPO temperature (kOhm) | P pol PLL (MHz) |
| 60 | 7.19 | 150 |
Then we scanned AOM frequency and measured green and IR transmission with diaggui. Note that this data is slow channel and sampled at 16Hz. Setting of AOM is shown in Pic 1. FM is 2 mHz and deviation is 1 MHz (peak to peak: 2MHz). During this measurement, we scanned green phase with 2kHz, 700mVpp. We also took a movie of green and IR camera to characterize higher order modes. Starting time is 19-07-02-07-08-57 UTC. Pic 2 shows transmission of green and IR. Higher order mode is as follows.
| time (s) | mode |
| 22.75 | TEM00 |
| 46.81 | pitch HOM |
| 72.5 | HG10,01 |
| 97.94 | HOM |
| 147.4 | TEM00 |
| 197.1 | HG10,01 |
| 248.6 | HG11,02 |
| 347.8 | HG10,01 |
| 423.2 | TEM00 |
| 472.8 | HG10,01 |
Note that speed of scan is 2 MHz / 250 s = 8 kHz/s and measured FSR is 147.4 - 22.75 = 124.65 s which means FSR is 0.9972 MHz in AOM.
As you can see, green transmission is also scanned by AOM since AOM scan changes alignment of green injected into filter cavity. But this shouldn't be a problem as long as alignment of filter cavity is fixed. When you look at TEM00 closely (Pic 3), sampling rate seems not enough. We'll try with oscilloscope today.
Yuhang, Pierre, Eleonora P, and Aritomi
In the beginning, Matteo and Eleonora modified the TAMA PD by apply two resistors and this amplifies the AC signal. This activity increased the SNR and make it possible to lock the coherent control loop.
Then I and Chien-Ming make this amplification even larger again, but the amplification increased both signal and noise. After this, we found there is a bandwidth limitation of AC channel op-amp when we increase the gain.
So we decide to use a higher speed op-amp and try to increase a bit the gain and to see if we can increase SNR furthermore. This replacement was did based on the modified PD improved by Chien-Ming. There were problems while Pierre was soldering the new op-amp. The copper board pin was fallen! But, fortunately, the lost pins are the pins which are not connected to anything else. Also, the day when we just finished the modification, we tested it on the bench but we didn't see any coherent control error signal. Actually, we found the very similar thing(cannot see BAB be amplified and de-amplified after OPO transmission) on the next workday. I and Aritomi-san we did the measurement of parametric (de)amplification measurement again while scanning the green phase with frequency slowly. After that, we could see everything well. We also realized at that time, the characterization of best OPO temperature/p-pol PLL locking frequency should be done maybe once a month.
After the replacement, we characterized the dark noise and compare it with the old dark noise before replacement. We found an increase of dark noise, we think this may come from the rise of a large current bias on the op-amp.
Then we measured the free-running noise and error signal noise spectrum (residual locking noise). The results are shown in the attached figures.
In the future,
we will also try to play a bit with the amplification of the AC signal. And also try to reduce the current bias of op-amp.
Error signal is 30 mVpp and conversion factor from V to rad is pi/0.03 = 105 rad/V.
[Takahashi-san, Yuhang, Eleonora C]
Last sunday afternoon (30/06) we recovered TAMA vacuum, air conditioning, dehumidifier system and DGS after the planned shutdown on 29/06.
Some details on the procedure can be found in the attached PDF.
Note that while I was In the end room I heard a short but very strong noise (as a small explosion). Takahashi-san told me that it is likely to be due to the presence of air bubble in the dehumidification water pump during the restarting process.
green setting:
| green power (mW) | OPO temperature (kOhm) | p pol PLL (MHz) |
| 40 | 7.175 | 174 |
IR into filter cavity is around 1 mW. TEM00 is as follows.
| AOM frequency (MHz) | IR transmission (cnt) |
| 109.03683 | 100-130 |
With 40mW green it was difficult to see higher order mode with IR camera. So we decided to increase green power.
On 27/06 Miyakawa-san came to Mitaka to try to fix the keyboard problem with the new DGS computer. (Since the gentoo linux cannot reconize the USB driver the keybord doesn't work). He tried to access the PC through the network but network port, but the kernel was too old to recognize it. It is not easy to update kernel because the kernel was patched to be a real time operation system. We also tried several USB PCIexpress board whitout success.
Anyway the actual standalone PC can host 4 ADC/DAC cards. Only two of them are currently used. We tested one of the new PCIexpress ADC board on the current stendalon PC and it seems to work fine. We decided to leave it installed.
The old ADC card is currently stored on the shelf close to the DGS rack.
In the near future we might need to install it too to increase the number of ADC channels. We agreed with Miyakawa-san and Akutsu-san that in this case we can use some of the hardwere from the ATC DGS which is currently unused.
In particular, in order to be able to use a second ADC we need 1 timiing adaptor, 1 AA module, 2 BNC-> Dsub coverter, cables. This will allow us to have 64 input channel.
Miyakawa-san showed me how to include additional ADC block in the simuling Real time model (NB: remember to copy the ADC block from library and not from those already in the model.)
He also helped to fix some minor issues:
1) remote connection to the DGS (Finaly we can access the system from the office and even from home!)
2) take/restore snapshot button on MEDM
3) rotation angle block
Yuhang and pierre
This work is motivated by the difficulty of locking the GRMC loop.
We measured again the loop, we found the resonant peaks have changed relative to the original measurement.
The first peak was changed from 7.23kHz to 6.9kHz and the second peak was changed from 11.85kHz to 9.9kHz.
We have already investigated by changing the position of clamps. But the peak position was not changed. However, I didn't try to move the end mirror of the mode cleaner. The change of these peaks position is still not clear.
Aritomi, EleonoraP, Yuhang
As described in the title, we characterized more about coherent control loop 1.
The dark noise is measured when there is not light. And other situation is the same(for example, PD is on, demodulation signal is on). The measurement point is error signal.
The free running error signal noise spectrum is measured after we checked that green phased shifter scanning and coherent error signal was fine.
EleonoraC, Takahashi, Yuhang
Today we have power outrage in TAMA, we switched off the vacuum system and air compressor yesterday. The procedure is similar to entry 1138. The list of things we did is summarized in the attached pdf file.
Here I also attached some numbers we need to recover later.
| power supply for AOM RF amplifier | 24V |
| RF driving frequency for AOM | 109.03535MHz 7dBm |
| power supply for homodyne | 19V |
| power supply for TAMA PD | 12V |
