NAOJ GW Elog Logbook 3.2
On Tue 29/11 we open INPUT vacuum chamber. Takahashi-san found the wire to the ground pin of the circuit of the top coil was broken. See picture.
He repaired it. We closed the chamber and check the the coil is working fine now.
[Yuhang, Aritomi]
We had homodyne noise spectrum bump problem reported in entry1529.
One of the reasons could be the cut issue of PD, and I checked the entry1159. I found that the 'beam analyzer' was put in a wrong position. The corrected version is attached here. In this version, the 'beam analyzer' is marking the position where the beam size(100um) is 5times smaller than the size of PD(500um). So we can decide that the homodyne PD should be 26mm~32mm after 30mm lens. This means we have only 6mm range to make sure the beam is smaller enough than the size of PD(500um).
We also measured again the shot noise after this work(attached picture 2 and 3). The bump issue sometimes is till present, but it covers region smaller than 20Hz and rarely show up. But we found small 45Hz and 54Hz peaks which are not present in previous measurement. They may due to we didn't cover bench as before(now the west side is half open and south side is open).
Today we had another failure of the BS TMP.
The error is number 089 which is for "Rotor vibration". The pump stopped autonomously.
After consulting with Takahashi-san we closed the gate valve between the TMP and the BS chamber as well as the valve between the BS TMP and RP and switched off the BS RP.
At this stage the pressure in the BS+PR was around 10^-3 mbar. In the input tower it was 10^-7 and in the arm 10^-8 (the gate valve around the input tower were still closed due to the work performed yesterday on the input mirror coil).
We open the gate valve between input and PB+PR and the pressure stabilized around 10^-4. So we let it go down few minutes until the pressure in input+BS+PR reached 10^-6 and then we opened the gate valve between the arm and the CITF. After that the pressure stabilized around 10^-6 and it is slowly going down.
In this moment there is only the pumping system of the input tower working for the central area.
This entry is log on 28th Oct.
I cut some teflon sheet for cushioning between glass window and adapter.
We measured the polarization map of OSTM with different polarization angles.
0 degrees represent pure p-polarization. 90 degrees represent pure s-polarization. 40.5 degrees represent a mixture of sp polarization with a ratio of 1 to 1.
[Matteo, Eleonora]
We used the code that simulates the homodyne spectrum for FDS at differente angles (entry #1774) and tried to optimize the angle to fit the data of our last FDS measurement (entry #1751)
The results in the attached figure show a quite good agreement between data (solid line) and simulation (dotted line)
The degradation parameters used in the code are the following:
sqz_dB = 16; % produced SQZ
L_rt = 100e-6; % FC losses
L_inj = 0.33; % Injection losses
L_ro = 0.11; % Readout losses
A0 = 0.1; % Squeezed field/filter cavity mode mismatch losses
C0 = 0.05; % Squeezed field/local oscillator mode mismatch losses
ERR_L = 5e-12; % Lock accuracy [m]
ERR_csi = 80e-3; % Phase noise[rad]
det = 50.62e3; % detuning frequency
int = 2e3; % frequency range = det+/-int
t_in_q = 0.0014; % input mirror transmission
gamma_fc = ((t_in_q + L_rt)/2)*fsr; % = 59.6*2*pi
To check how much second harmonic of 7MHz CC/LO beat note affects 14MHz CCSB beat note, I put TAMA RFPD before AMC and detected LO and CC at the same time. CC is directly injected from OPO and CC1 is locked. I compared 14MHz peak height with only CC or CC+LO. Pic. 1,2 shows 14MHz signal with only CC or CC+LO. Apparently 14MHz peak height is almost same.
Then I demodulated the 14MHz signal with 14MHz and measured spectrum of the demodulated signal (Pic. 3). Spectrum with CC+LO has some excess noise compared with only CC and the noise shape seems similar to CC2 phase noise. This noise should come from second harmonic of 7MHz.
Today I temporary installed the adapter flange and 4K shiled inside the cryostat chamber to confirm the screw hole position is correct.
The adapter flange and shield seemed to be O.K., but I need 10 more ultrasonic cleaned M6 screws.
In addition to that, we need super insulator on 4K shield and tape to fix cables.
The procudure for remaining tasks are:
- Prepare windows for 80K shield
- Install windows on 80K shield
- Cabling on 4K shield
- Attach SI on 4K shield
- Install 4K shield
I adapted the code to simulate the squeezing degradation in the case of standalone filter cavity. Basically, I removed the transfer matrix accountig for ITF in the quantum noise computation.
Now if we select a homodyne detection angle the code should simulated what we exepected to see when taking the spectrum of the Homodyne output.
In the code I also removed the approximation of small detuning and I simulate a large detunig case (50kHz) as the one we tested recently. (Entries: #1747, #1751)
Plot 1 shows the expected results for Homodyne angle: 0 deg and 90 deg. Plot 2 shows an intermediate case (30 deg) compared to the 0 deg case.
The degradation parameters are the same reported in entry #1766.
I stopped the baking at 14:30. It was applied for 4 hours in this time.
I set the thermostat to control the temparature of heater. The set temparature is 110 oC. I started the baking of BS TMP from 10:30AM.
I stopped the baking at 14:30. It was applied for 4 hours in this time.
Most of the RMS is accumualted below 10 Hz. We observed a correlation between the PDH error signal for IR (demodualtion of 15 Mhz sidebands) and the lock correction signal from RAMPEAUTO.
At the time of the measument we know the IR alignment was not good. This can be the cause of such behaviour. We should repeat this measurement in good alignment condition.
Attached to this report are the polarization maps on OSTM from Sigma Koki.
The maps are taken with different polarization angles indicated in each figure, with 0 degrees being pure P-polarization.
[Aritomi, Yuhang, Yaochin, Eleonora]
We measured IR error signal of filter cavity using BAB with TAMA PD which is same as CC1 PD in the reflection path from filter cavity. Pic. 1 shows IR error signal and IR transmission when filter cavity is scanned with AOM (setting is Pic. 2). Calculation method of calibration factor is same as entry 750.
Note that factor of 2 in calibration factor is because slope of error signal on resonance is as twice as slope of peak-peak of error signal.
Then we measured spectrum of IR error signal when IR is locked on resonance and calculated rms (Pic.3). IR locking accuracy is 4.2 Hz which corresponds to 4.5 pm of locking accuracy. Pic. 4 shows squeezing degradation with this locking accuracy. In addition to mode mismatch, locking accuracy is also dominating. We need IR locking.
Most of the RMS is accumualted below 10 Hz. We observed a correlation between the PDH error signal for IR (demodualtion of 15 Mhz sidebands) and the lock correction signal from RAMPEAUTO.
At the time of the measument we know the IR alignment was not good. This can be the cause of such behaviour. We should repeat this measurement in good alignment condition.
[Namai-san, Ueda-san from KEK, Sato-san, and Tomaru-san]
We worked on the cryostat in ATC to install adapters for windows on 80K shield.
What we did is as follows:
- Attached the adapters on 80K shield
- Adjusted the insulator on 80K shield not to touch the 300K shield
- Removed 300K shield for temporary and install 80K shield
- Re-installed 300K shield
- Re-located the chamber to install the cold head and bellows
- Installed an optical breadboard and connected to cold head with grease
Since we don't have indium sheet, we used grease to contact with cold head.
Though this grease can be used in vacuum (~10^-7 Pa), if the contamination on mirrors become a problem, we will remove the grease and use indium sheet.
The remaining tasks are:
- Install modified 4K shield, and windows on 80K shield
- Cabling
- Vacuum check
Today I temporary installed the adapter flange and 4K shiled inside the cryostat chamber to confirm the screw hole position is correct.
The adapter flange and shield seemed to be O.K., but I need 10 more ultrasonic cleaned M6 screws.
In addition to that, we need super insulator on 4K shield and tape to fix cables.
The procudure for remaining tasks are:
- Prepare windows for 80K shield
- Install windows on 80K shield
- Cabling on 4K shield
- Attach SI on 4K shield
- Install 4K shield
This entry is log on 28th Oct.
I cut some teflon sheet for cushioning between glass window and adapter.
I checked homodyne RF signal if I can get 14MHz CCSB beat note, but I couldn't find 14MHz signal in homodyne RF. 14MHz signal may be filtered out by low pass filter after demodulation inside homodyne. We have to modify homodyne if we want to detect 14MHz at homodyne...
[Aritomi,Yuhang,Yao-chin, Eleonora]
The attached plot shows a very tentative degradation budget for the squeezing injection into FC detuned at 50 kHz (entry #1751)
PRODUCED SQUEEZING: 16 dB (from anti squeezing measurement) (entry #1587)
TOTAL INJECTION LOSS = 33 %
- from inside OPO to 1st PBS = 18% (loss of frequency independent squeezing: 21% - visibility: 2% - quantum efficiency: 1%)
- after 1st PBS before PR chamber = 10%
- from PR viewport up to FC = 5 %
TOTAL READOUT LOSS = 12 %
- from FC to PR viewport: 10%
- after viewport to Homodyne: 1%
- Homodyne Q. E. = 1%
MISMATCH from SQZ to FC = 10 %
MISMATCH from SQZ to HOM = 5 %
FILTER CAVITY LOSSES : 100 ppm
PHASE NOISE = 100 mrad (very tentative, when CC2 doesn't unlock)
LOCK ACCURACY = 5 pm (very tentative, to be measured)
Conclusion: it seems that the degradation is dominated by mismatching
[Aritomi, Yaochin]
We put TAMA PD in the reflection path from filter cavity and detected CCSB 14MHz beat note and demodulated it with TAMA demodulator. Filter cavity is locked with green and CCSB are off resonance. For demodulation LO, we used CC1 demodulation LO. Then we scanned green phase going to OPO which scans relative phase of CCSB. This relative phase scan of CCSB emulates CCFC error signal.
Note that we only have 90:10 RF BS and when we used this RF BS to divide CC1 LO and used 10% of CC1 LO for this filter cavity error signal, there was no error signal. We'll buy 50:50 RF BS.
Pic.1: CCFC 14MHz signal
Pic. 2: CCFC 14MHz signal after RF amplification (34dB)
Pic. 3: CCFC error signal for filter cavity when CCSB are off resonant and green phase is scanned
[Yuhang, Yaochin, Aritomi, Eleonora]
We wanted to check the gain of the quadrant PD by shining some light on it and look at the response of the RF channel with a spectrum analyzer. We assumed that amplitude fluctuations at that high frequencies are shot noise dominated and thus have a flat spectrum. It this way it would be possible to measure the gain TF of the PD and indentify its resonances.
We sent to one sector of the quadrant about 1.5 mW of green light in reflection from FC and we amplified the RF signal of 32dB. We couldnt' see any difference in the spectrum with respect to the case when we don't send any light, except for the light at the modulation frequency that we could not switch off (15 MHz, needed for SHG).
We decided to take the same measuremnt with a red laser diode, in the same configuration for differen power value. We found that the RF spectrum level increases with the power showing a peculiar shape.
We observed that the RF signal stop increasing already at about ~250uW, while DC seems linear (see first plot)
Not that the responsivity of the sensor is similar for green and red (0.2 [A/W] wrt 0.25 [A/W])
In order to confirm that the laser diode has not any strange amplitude feature at high frequency, we tried it on a QUBIG PD and found a reasonable RF spectrum with a cut off at 100 MHz ( as reported by the data sheet)
Conclusion: something is wrong. The quadrant seems to repond too differently to green and red light. But the gain doesn't show any resonace. We will investigate more.
