NAOJ GW Elog Logbook 3.2
After the measurement of the QPD spectrum with BS oplev in elog2532, we then measured the QPD linear range. We centered the beam on the QPD and checked the linear range while offsetting the beam position up, down, left and right.
When returning the beam position to "zero", the QPD reading didn't return to the zero value measured at the start of each run. So there is a bit of effect from suspended optics drift. This is why I split the data into 4 directions rather than just pitch and yaw.
Also, the QPD readings have a variation of about +/- 200 in pitch and ~+/- 300 in yaw.
I made a measurement of oplev laser power for PR/BS/INPUT/END.
They are 270uW (PR), 320uW(BS), 70uW(input) and 107uW(end).
According to the datasheet of thorlabs PSD, the maximum power should be around 66uW.
Oplev laser power has been set in order to be compliant with PSD specs. Since the laser diode that we use doesn't have the possibility to control the power, ND filter were added to this purpose.
User manual of the PSD can be found here: http://www2.nao.ac.jp/~gw-elog/osl/uploads/278_20160721110810_pdp90a.pdf
Michael and Yuhang
To test the available space and compare the performance of KAGRA QPD with thorlabs PSD, we did the test for INPUT.
1. We found all mirrors are not fixed well inside the mirror mounts. For example, we could easily push them out by hand.
2. We found several ND filters were used to reduce oplev light power. We took measurement with all ND filters or none of them.
The comparison is in figure 1. We could see that KAGRA QPD has a better SNR while the same oplev laser power is used. By increasing oplev laser power, an even better SNR could be achieved. The spectrum below 10Hz is quite similar but some new peaks appear at high frequency.
Apart from these, I have some questions.
0. Are we aiming for a better SNR with KAGRA QPD? If so, why don't we just increase oplev laser power?
1. Why we use ND filters to reduce oplev laser power? Is there any limitation for oplev laser power?
2. Are the screws to fix mirror inside mirror mount easily loosen by themselves? If so, we should check for other oplevs and mirrors on bench.
Note: after this test, we have bring system (simulink files and oplev set-up) back to the original situation.
Oplev laser power has been set in order to be compliant with PSD specs. Since the laser diode that we use doesn't have the possibility to control the power, ND filter were added to this purpose.
User manual of the PSD can be found here: http://www2.nao.ac.jp/~gw-elog/osl/uploads/278_20160721110810_pdp90a.pdf
I made a measurement of oplev laser power for PR/BS/INPUT/END.
They are 270uW (PR), 320uW(BS), 70uW(input) and 107uW(end).
According to the datasheet of thorlabs PSD, the maximum power should be around 66uW.
According to the manual, thorlabs PSD (which are installed on the input and on the end mirror) should have a power level so that the SUM output voltage is ≤ 4 V.
Is this the case?
BS and PR are equipped with different PSD (TAMA ones) which can accept higher power.
Yes, I checked this voltage. With current power, it is 2.8V. This is already quite close to 4V, so we don't have much space for improvement.
Anyway, I tried to remove one ND filter to have 4V, but the spectrum is quite similar with the 2.8V one.
PR and BS can accpet more power, but most of the light was lost since the suspended mirror surface is not HR for 635nm. So we couldn't have more power.
We have used channel 17-20 of the lower AA chassis, which was originally PR p/y/s and BS p. The four signals from four segments of KAGRA QPD are using them.
A marix was designed to convert them into p/y/s. And then it is connected to BS block.
Accordingly, channel 21 and 22 were changed to be connected to PR block (as in the attached figure).
The whole modification is shown in the attached figure, will be changed back after QPD test.
Matteo, Yuhang, Marc, Aritomi
Today the TAMA vacuum system has been partially recovered.
The vacuum level before starting the recovery was 22mbar both in the arm as well as in the central area and in the South end tower.
The status of the vacuum pumps was as follow:
- BS: rotary and turbo fine and working
- South near: scroll and turbo fine and working
- South mid: scroll and turbo fine and working
- South end: scroll fail and turbo off
All the pumps were isolated by gate valves. The gate valve at South near between arm and central area was closed and the arm+South end was evacuated using the big movable rotary pump.
After reaching a pressure of about 1e-2 mbar, the movable rotary pump was removed and the gate valve between the arm and the South near was opened, as well as the South mid gate valve between the arm and the turbo pump. After performing this operation the pressure in the arm reached 2e-5mbar at South near and 1e-4mbar at South end.
After this also the central area was evacuated using the movable rotary pump and using the same procedure just described, the central area was evacuated to a level of 1e-3mbar. At that time, since the pressure in the central area and in South near was almost the same, the big gate valve between central area and south arm was opened.
Before leaving the vacuum level was about 1e-5mbar in the central area and 8e-5 in South end.
All the vacuum pump are working properly with the exception of the South end dry pump which is still giving error message. The turbo pump at South end is off and isolated from the arm.
It was pointed out that the measurement of oplev p/y spectrums are not meaningful. So I went to check again what can be the problem. In the end, I found the laser head of the oplev is totally loose. After I fixed it, I took spectrums again. Figure 1 shows these spectrums.
Besides, I also put some pictures of the KAGRA QPD set-up. (note that we could close the black box, pictures are just taken with box open) (we will use a better box in the future if we really use this QPD)
I tried to close BS local control with KAGRA QPD.
The comparison of pitch/yaw spectrum when loop is open or closed is in the attached figure.
Michael and Yuhang
We checked the QPD signal from each segment, which is consistent with the matrix we set for channels.
We also compared with TFs of BS pitch/yaw with old measurements. This comparison is in figure 1 and 2. From this measurement, it seems that QPD is working well.
The detuning frequency has been set in elog2296 by Aritomi-san. According to that value, I calculated several different numbers which could be used to set even higher detuning.
|
Detuning |
Frequency_cc (MHz) |
Binary number |
2*Frequency_cc (MHz) |
Binary number |
3*Frequency_cc (MHz) |
Binary number |
|
64Hz |
6.99700252 |
11-10010101-00011100-01110010 |
13.99400504 |
111-00101010-00111000-11100100 |
20.99100756 |
1010-10111111-01010101-01010110 |
|
74Hz |
6.99699251 |
11-10010101-00011100-00011100 |
13.99398502 |
111-00101010-00111000-00111000 |
20.99097753 |
1010-10111111-01010100-01010100 |
|
84Hz |
6.99698250 |
11-10010101-00011011-11000110 |
13.99396500 |
111-00101010-00110111-10001100 |
20.99094749 |
1010-10111111-01010011-01010010 |
|
94Hz |
6.99697249 |
11-10010101-00011011-01110000 |
13.99394497 |
111-00101010-00110110-11100000 |
20.99091746 |
1010-10111111-01010010-01010000 |
|
104Hz |
6.99696247 |
11-10010101-00011011-00011010 |
13.99392495 |
111-00101010-00110110-00110100 |
20.99088742 |
1010-10111111-01010001-01001110 |
|
114Hz |
6.99695246 |
11-10010101-00011010-11000100 |
13.99390493 |
111-00101010-00110101-10001000 |
20.99085739 |
1010-10111111-01010000-01001100 |
|
214Hz |
6.99685246 |
11-10010101-00010111-01101001 |
13.99370492 |
111-00101010-00101110-11010010 |
20.99055739 |
1010-10111111-01000110-00111011 |
According to elog2350, the detuning values in this elog should be 105Hz, 115Hz, 125Hz, 135Hz, 145Hz, 155Hz, 255Hz.
Michael and Yuhang
Since we always have TAMA old PSDs broken and suspect AA noise coming from PR/BS oplev, we decide to buy new PSD/QPDs. Akutsu-san provided us two QPDs from KAGRA, we report the test of one of them in this elog.
The tested QPD is JGW-D1402411-v2.
We powered it with a DC voltage supply, the current consumpation is 0.069A for -15V while 0.084 for 15V.
We set this PD for BS oplev and compared with the measurement from TAMA PSD. Figure 1 shows this comparison. We could see that a better SNR can be achieved from KAGRA QPD. Besides, if we used a higher gain in KAGRA QPD, we gain even better SNR below ~50Hz. However, one strange thing is that the yaw spectrums show different peak structure for QPD or PSD.
Marc and Yuhang
On Monday, we found CC PLL couldn't be locked. We checked the RF signals, LO signals, locking loop set-up and correction signals.
LO signal is about -2dBm. Locking loop set-up was reloaded. Correction signal seems to be saturated. In the end, we found the RF signal was very small.
Although this may be related with just alignment, we decide to replace fiber since I remember there is a damage of CC PLL fiber (see fig 1).
The new fiber is fixed on top of AA breadboard, which makes it easier to be checked in the future. (see fig 2)
The RF signal reaches PLL lock loop is about -8.5dBm with new fiber and amplifier. (see fig 3)
The monitor channel shows -33dBm on the lower spectrum amplifier (see fig 4). Note that the fiber PD used for monitor is battery powered, which seems to be able to provide only RF signal.
Michael and Yuhang
Yesterday, we locked AA, Zcorr, pointing and CCFC and performed a FDS measurment. The lock last for almost one hour. 6 measurements were performed during this time (with a separation of almost 10min).
The result is shown in the attached figure 1.
Within this 1 hour, all measurements overlap very well. Even the low frequency back scattering seems to be more stable.
(50:50 BS was used for CCSB pick-off. 30mW pump power is used for SQZ production.The detuning was expected to be 104Hz according to elog2353.)
(Figure 2 shows a FDS measurement of detuning smaller than 100Hz, it seems backscattering makes FDS not reaching shot noise level. This is also why we took several measurement with higher detuning.)
(Figure 3 shows a fit for higher detuning. Since the detected detuning is 145Hz, we expect all the frequencies to be increased by 40Hz in elog2353. )
Marc and Yuhang
We checked OPO CC power in transmission with different green power injected.
The injected CC power is 1.52mW. In transmission, 3.9uW of offset has been removed (coming from p-pol).
Reflected CC power (no green) is picked out by a 25:75 (R:T) BS. The pick-off power reaching CC1 PD is about 133uW, which is strange. Since we know that OPO makes 99.7% CC reflected and 25% of pick-off, we expect 379uW reaching CC1 PD.
Marc, Yuhang
Yesterday, when we just entered the cleanroom, we realized that the main laser head was quite hot (by hand). However, we found the laser was fine (the laser was on, and we could lock SHG). So we didn't care so much about that.
However, after we used the main laser for a short period, the main laser suddenly went off. Almost one week ago, we reported the main laser sudden off. We didn't know the reason. In total, we found three times of laser off in the recent month.
After the laser suddenly off, we found that we couldn't turn it on by pressing the switch. So we put a thermal meter on top of the laser head and wait for a while. Figure 1 shows the laser head temperature change during this waiting time. Then we turned the main laser key off. After turning it on, the laser starts to work well.
Recently we found another issue related to the main laser. More than two years ago, we did an investigation of our main laser stability (elog). After three hours of operation, laser power becomes very stable. But now, even after one day, the power stability is not very ideal. Figure 2 shows this laser power change. Although this is not a big issue for squeezing production since its frequency is quite low, this may mean we are having small problems.
After switching the laser on, we monitored laser power again and found laser head temperature increases back. Figure 3 shows this laser power change. This temperature change is related to the laser power change since they have almost the same frequency. We will check this coherence in the future.
Marc, Michael, Yuhang
Matteo ordered BSF10-C to pick off CCFC error signal from filter cavity reflected squeezing. This mirror should take about 2% power, which means small optical losses for not degrading squeezing field. Today, we replaced the old 50:50 BS with this BSF10-C. We report several check we did here.
1. By using BAB and power meter, we checked power splitting ratio of BSF10-C. Incident power is 325uW, reflected power is 7uW, transmitted power is 321uW. From this measurement, the power loss is about 1~2%.
2. We checked CCFC sideband. When 40mW green is incident inside OPO, we have CCFC sideband as figure 1.
3. We compared CCFC error signal before and after replacing beam splitter. Figure 2 (after) and 3 (before) show them. We could see that error signal becomes not usable after this replacement.
4. We tried to amplify CCFC signal from photodetector, we got new sideband as figure 4. But, as figure 5, the demodulated error signal just became overall larger.
I also attach here, as the last figure, how much FDS level we expect when we use different pick-off beam samplers. But since we just want to demonstrate this technique, maybe the current 50% BS is enough to see squeezing and stabilized detuning.
Marc (remote), Eleonora (remote), Yuhang
In elog2341, we reported the INPUT oplev was not set-up properly. I checked signal connection and found that input and output of SR560 were swapped. After solving this problem, INPUT oplev was recovered. (SR560 used gain as 100 and no filters) In the end, I compared INPUT oplev signals. Figure 1 shows this comparison, which shows a lower noise level.
Michael, Yuhang
After installing RF amplifiers and USB switches, we worked on the recovery today.
1. We reboot standalone to solve the problem of timing
2. We delete some second trend and released 10% space (this corresponds to about 1 month data)
3. We checked PLL p-pol frequency changed to 265MHz (53) with OPO 7.162 temperature and no green. It was 240MHz (48). In this case, BAB power before PBS is 0.46mW.
4. The mode matching from BAB into filter cavity was checked to be better than 93% (520 counts was observed for FC BAB tra)
5. Then we found main laser turned off by itself. We didn't notice how it happened. Then we checked dataviewer. The PR/BS/INPUT/END oplevs, FC GR/IR tra, FC GR correction/error were checked. Figure 1 shows this check. From this check, we could find
- The first change happend for FC GR/IR tra, FC GR error suddenly.
- PR oplev didn't have any change. BS oplev changed gradually due to pointing loop. INPUT oplev didn't change because of its wrong set-up. END oplev didn't have sudden change, either. So this main laser sudden off should not come from suspension.
- FC GR correction looks not that sudden compared with GR tra. So this problem seems also not come from a sudden large laser frequency or cavity length change.
So it is still not for sure why we see this change.
Michael and Yuhang
In elog2336, we checked RF signal generated from DDS2, we found some sidebands around the generated RF signal.
Today, we checked RF signal from DDS3. Attached figure shows this check.
We could see that this peak is much cleaner.
Marc, Michael and Yuhang
After yesterday's investigation, we found although RF signal is not very clean, but it doesn't have large noise. So we were thinking the 20kHz noise should be just at low frequency and it goes to many other places. For example, elog2330 shows this noise from DDS filter-out even when there is no signal. Besides, elog2331 shows this noise from power supply of DDS board. An important fact was ~20kHz noise is only related with the connection of DDS board.
So we tried to connect individual voltage to DDS board one by one. Then we found out that ~20kHz noise shows up only when voltage is provided to USB. So we could infer that ~20kHz noise comes from USB voltage supply. Although we still don't quite understand what is the exact reason of introducing this noise, we could avoid having this noise by disconnecting USB voltage supply. This is also feasible because we don't need to connect USB so often.
Then we found a solution. We decide to use a switch, which decide whether the voltage will be provided to USB or not. But note that don't connect all USB if the DDS software is open. This is also good because this makes it easier to operate DDS boards. Before this modification, we need to change USB connection by hand if we want to control different DDS board. Now it becomes easier, we use switch to decide which DDS board to be controlled. If we don't need control DDS, we need to switch USB voltage off for avoiding noise.
After applying switches to DDS boards, we did comparison with USB voltage off and on. Figure 1 shows this comparison. We could see that noise frequency is changed. But anyway, if USB voltage is off, we will have 'clean' SHG error signal.
