NAOJ GW Elog Logbook 3.2
[Aritomi, Yuhang]
We checked the nonlinear gain with 25mW green (MZ offset: 4.2), but it is only ~2. It was 6.8 one year ago in elog2577. We optimized green alignment to OPO, OPO temperature, and p pol PLL frequency, but the nonlinear gain is still around 2. Here is the summary of today's measurement.
| green power (mW) | 0 | 25 | 25 | 25 | 25 |
| OPO temperature (kOhm) | 7.166 | 7.166 | 7.156 | 7.146 | 7.136 |
| p pol PLL (MHz) | 295 | 255 | 235 | 220 | 200 |
| BAB maximum (mV) | 98.4 | 216 | 226 | 230 | 232 |
| Nonlinear gain | 1 | 2.2 | 2.3 | 2.3 | 2.4 |
Yuhang, Aritomi
1. We tried to send 500mVpk-pk sine wave to main laser intensity modulation channel. It was not clear how much is the bandwidth for this channel. We will check this next time. In any case, the frequency was set as 10kHz.
2. We put ND1+ND0.5 filter for LO before homodyne. The voltage measured on the homodyne first eye is 220mV. We measured LO spectrum on homodyne eye one as H1ND2.txt.
3. We removed one ND0.5 filter. The voltage measured on the homodyne first eye is 659mV. We measured LO spectrum as well, named as H1ND1.txt.
4. We send 800Hz 700mVpp to IRMC locking servo noise injection point. And optimize noise subtraction manually.
5. We put back 500mV noise to laser intensity, then measure homodyne sub-DC spectrum as LONOI.txt. In this condition, no ND filter was used.
6. We measured LO sub-DC spectrum as LO0NOI.txt when there is no noise sent.
7. We measured homodyne sub-DC in this situation (from ~0.1Hz to 200Hz) (a temporary check indicates that it is about 70dB at least. We will inject more noise next time to see if we can achieve better CMRR.)
We try to measure the laser power using power meter.
We find that laser power is too low comparing spec sheet.
We use laser diode "L520P50".
We inject 124mA.
According to spec sheet, laser power is 50mW.
However, laser power is almost 10mW.
And laser shape is bad and not collimated with collimator lens.
Because the ratio scattering light and inject power is most important, we try to measure scattering of Aztec#3.
Laser power is,
Before iris:8.15mW
After sample:4.55mW
Reflection light:415uW+331uW(415uW is front surface)
In this figure, scattering light is in the yellow box.(Blue box is reflection light by mirror surface)
Below 1Hz, microseismic band, the ASD is large on Saturday night. It is consistent with the ocean wave.
At around 3Hz, the ASD is large on Saturday night and Monday morning, and small on Sunday.
Between 10 Hz and 20Hz, the ASD is large on Monday Morning.
Around 30 Hz, sometimes strange bumps are observed.
I checked pitch/yaw TF for all mirrors and coil response for all magnets. PR/BS/END are fine.
For INPUT, input oplev spectrum was strange (Fig. 1). Yaw seems fine, but pitch had a huge 50Hz peak. I checked the dark noise and there was no huge 50Hz peak, so the 50Hz peak came from oplev laser source. I power cycled the oplev laser source and then the 50Hz peak disappeared (Fig. 2).
I checked the input pitch/yaw TF. Both of them are smaller than before by a factor of 10, but the shape is fine. I also checked each coil response. They seem fine, but yaw TF is larger than before by a factor of 10 in H2, H4.
[Takahashi, Aritomi, Yuhang, Michael]
Since the END picomotor didn't move, we opened END chamber and aligned FC. We aligned PR and BS to make the green at center of GV between input/BS and at the upper left of first target as reported in elog2935. After we scanned BS alignment, we found the beam at second target.
Then we checked the behavior of END picomotor with old picomotor driver by looking at the green reflection from END mirror at the second target. We connected pitch picomotor to motor A and yaw picomotor to motor B. There are two settings of joystick: SET X and SET Y. In SET X, whatever the selected motor, when we move the joystick in X direction, the beam moves in yaw and when we move the joystick in Y direction, the beam moves in pitch. In SET Y, we can select the motor and the selected picomotor can be moved by moving the joystick in Y direction. We don't understand the bahavior of SET X, but we should use SET Y of joystick. We also confirmed that all motors of old picomotor driver are working.
To obtain the END oplev signals, we brought back the Dsub cable from PEM to END oplev signals. We found that when the END oplev beam is blocked, END oplev X and Y show around 2100 and -800 counts, respectively. After we centered the oplev around these values, we checked pitch/yaw TF. The pitch TF was fine (Fig. 1), but yaw TF was strange (Fig. 2). We found that yaw TF becomes fine when we flipped the sign of EUL2COIL matrix for H3 (Fig. 3). When the sign of EUL2COIL matrix for H1 is flipped, the sign of yaw TF is also flipped. We also checked the response of H1, H3 magnets with health check script (H1: Fig. 4, H3: Fig. 5), which also shows the sign of H3 magnet is flipped. This flipping happened when we glued it in elog2900. We flipped all the sign of EUL2COIL matrix for H3 (before: Fig. 6, after: Fig. 7).
Finally we closed the chamber. We will start evacuation tomorrow.
Important note: After we glue the fallen magnet, we should also check the sign of the magnet. If the sign of the magnet is flipped, we need to flip the sign of EUL2COIL matrix for the magnet.
Today I repeated the characterization of an 'unknown sample' (a HWP) using motorized HWP and translation motor.
First, the calibration gave X_cal = 13.3 mm which is compatible with the previous estimation.
Then, I measured the unknown sample retardance to be 0.496 which is expected value.
Next step will be to be able to access photodiode signal on the PC to start the LabView automatization.
Seismic data of KAGRA is under OMC chamber and the microphone is in the IMC refl.
The large peak at one-handed several-tens Hz of the seismic data is the self-noise. (data sheet)
We try to measure scattering of Aztec 3.
We can take a picture of scattering light.
In this figure, scattering light is in the yellow box.(Blue box is reflection light by mirror surface)
We performed the hammering test for the FC optics, to investigate the origin of the 170Hz noise.
50n Hz peaks are AC power and its harmonics.
The Eigen frequencies of the optics are higher.
The most suspicious object was the chamber.
We brought the PEM sensors from KAGRA to TAMA temporally.
* Trillium compact seismometer and its cable
* Whitening filter with DC power supply and D-sub 15pin cable
* ACO microphone, ACO 4ch power supply, and BNC cable
* 3-axis accelerometer and its cable
We connected the seismometer and the microphone to the ADC ports.
* K1:FDS-ADCspear_1_OUT_DQ -> Low frequency microphone
* K1:FDS-END_in_HOR_fil_IN1 -> Seismometer East-West
* K1:FDS-END_in_SUM_fil_IN1 -> Seismometer North-South
* K1:FDS-END_in_LEN_fil_IN1 -> Seismometer Vertical
The attached plots are seismic and acoustic data.
The units are "count", not calibrated to um/s more Pa.
Seismic data of KAGRA is under OMC chamber and the microphone is in the IMC refl.
The large peak at one-handed several-tens Hz of the seismic data is the self-noise. (data sheet)
Below 1Hz, microseismic band, the ASD is large on Saturday night. It is consistent with the ocean wave.
At around 3Hz, the ASD is large on Saturday night and Monday morning, and small on Sunday.
Between 10 Hz and 20Hz, the ASD is large on Monday Morning.
Around 30 Hz, sometimes strange bumps are observed.
A comparison of RIN, shot noise and photo detector dark noise is shown in the attached first figure for several locations on the squeezer bench. Other figures show these noises for different single location separately.
[Takahashi, Aritomi, Yuhang]
Since BS suspension motion was too large and the pitch picomotor can move in only one direction, we opened BS chamber and checked suspension. Takahashi-san found that the magnet was touching the coil holder so he adjusted it.
Regarding the picomotor, the picomotor cannot move in one direction because the required force to move the picomotor in the direction was too large. To reduce the required power to move the picomotor, Takahashi-san put a spring (Fig. 1). Then the picomotor can be moved in both directions.
We aligned PR and BS to make the green beam at center of the GV between input/BS and the first target.
Before closing the chamber, we checked BS oplev transfer functions (Fig. 2,3) and response of each coil. The transfer function and coil response are fine.
Finally we closed the chamber and started the evacuation of BS chamber.
Dan Chen, Marc
Today we assembled on the 75 * 90 cm optical table the frame of the dark box inside which we will perform the scattering measurement.
We also placed AZTEC #1 and #3 on holders inside the frames.
Report about AZTEC #4 absorption.
It seems to be around 100 ppm/cm and some fishbone patterns are visible as well.
A proper beam dump thorlabs LB2 (1um - 12um) is installed for the newly replaced BS mount (as shown in Fig.1).
Although we can see some green light, let's remind that it is because the camera sensor is more sensitive to green as our eye. There are proper Dichroic mirrors to remove them.
Yuhang, Aritomi, Marc
A new PD (PDA36A-EC) is used (gain is chosen as 0dB), firstly DARK NOISE is measured (saved as DARKL.txt and DARKH.txt)
A LA1608-YAG lens (75mm) was always used when the beam is apparently large.
1. Measure Mephisto RIN. It is measured at the location where we pick off main laser for CC PLL LO.
The DC voltage is measured as 2.66, 2.61V and 2.67V (measured before and after spectra measurements). (saved as MAINL.txt and MAINH.txt)
2. Measure homodyne LO RIN. It is measured just after IRMC transmission.
The DC voltage is measured as 800mV, 780mV (measured before and after spectra measurements). (saved as LOL.txt and LOH.txt)
3. Measure SHG generated GR RIN. It is measured before MZ.
The DC voltage is measured as 3.14V, 3.16V, 3.24V (measured before and after spectra measurements). (saved as SHGL.txt and SHGH.txt)
This is an experiment record. An analysis of data will come later.
First we replaced the broken BS oplev PSD and measured BS oplev spectra as shown in the attached figure. The noise floor of BS oplev spectra is fine, but BS suspension moves a lot. In addition, BS pitch can go down with picomotor, but cannot go up. We need to open BS chamber again...
We somehow aligned FC and could see the green flash, but green beam spot at FC transmission moves too much due to BS suspension motion.
Then we found that we cannot maximize TEM00 very well and yaw misalignment cannot be removed.
We aligned green injection in yaw before as reported in elog2940. We doubt that this could cause some problems. So we tweaked the green injection, but the green flash still had yaw misalignment. After we brought the green injection back to the original alignment, END yaw was misaglined a lot and we had to move the END yaw with picomotor. We went to END room and moved END picomotor with a joystick. However, at some point, END yaw picomotor stopped moving and we lost green flash...
To do list for END mirror:
- center END oplev and check END oplev spectra/transfer function
- install a new picomotor driver to avoid going to END room for picomotor control
- If END oplev spectra are strange or picomotor does not move with the new picomotor driver, open END chamber and check the suspension and picomotor
The OPO pump relative intensity noise was measured at different power level.
1. MZ offset 4.2 (25 mW), DC voltage on oscilloscope 320mV
2. MZ offset 4.4 (35 mW), DC voltage on oscilloscope 441mV
3. MZ offset 4.0 (15 mW), DC voltage on oscilloscope 186mV
As a reference, in LIGO, the SHG RIN is about 3e-6 from 3Hz to 400Hz. Then it gradually increases to 3e-5 at 4kHz. This indicates that the control servo has 1/f slope. (alog45088)
So we have a better RIN at low frequency (limited by PD dark noise). But a worse RIN at kHz region.
Yuhang, Aritomi, Marc
A new PD (PDA36A-EC) is used (gain is chosen as 0dB), firstly DARK NOISE is measured (saved as DARKL.txt and DARKH.txt)
A LA1608-YAG lens (75mm) was always used when the beam is apparently large.
1. Measure Mephisto RIN. It is measured at the location where we pick off main laser for CC PLL LO.
The DC voltage is measured as 2.66, 2.61V and 2.67V (measured before and after spectra measurements). (saved as MAINL.txt and MAINH.txt)
2. Measure homodyne LO RIN. It is measured just after IRMC transmission.
The DC voltage is measured as 800mV, 780mV (measured before and after spectra measurements). (saved as LOL.txt and LOH.txt)
3. Measure SHG generated GR RIN. It is measured before MZ.
The DC voltage is measured as 3.14V, 3.16V, 3.24V (measured before and after spectra measurements). (saved as SHGL.txt and SHGH.txt)
This is an experiment record. An analysis of data will come later.
A comparison of RIN, shot noise and photo detector dark noise is shown in the attached first figure for several locations on the squeezer bench. Other figures show these noises for different single location separately.
The CMRR was characterized by sending 10kHz 500mVpk-pk noise to laser intensity. To get the CMRR value, we compared two situation. One is when the LO is sent to only one eye of homodyne, but ND1 was used to make sure no saturation. Therefore, if the ND1 is removed, the noise should be increased by 20dB. The other situation is as usual way to measure shot noise, which is to measure sub-DC spectrum. The result is shown in Fig.1.
Then we also took a shot noise measurement at low frequency. The shot noise becomes flat until 3Hz (Fig.2). This is reasonable considering that the LO RIN measured in logbook 2988 shows almost 40dB RIN increase from 20Hz to 1Hz. Although we didn't have a clear number of CMRR in the past, we know that we achieved flat shot noise until 10Hz. Compared with the old usual shot noise, we should need more than additional 40dB CMRR to achieve shot noise like Fig.2.
Personal note: the 80dB CMRR is actually limited by the noise we can send to main laser intensity. Remind that the intensity noise modulation channel has an efficiency of 0.1A/V. So when we send 0.5V, we are actually modulating by only 0.05A the laser current. I think we can at least increase this noise by a factor of 10. But I checked the manual of our laser and I haven't found what is the damage threshold for this channel. This needs to be confirmed.