NAOJ GW Elog Logbook 3.2
Aritomi, YaoChin and Yuhang
We closed the bench shield of main laser side(as shown in the attached picture). Now the only side we are not closing is the GR/IR injection side. Before closing, we need to drilling several holes on the board for GR/IR beam.
[Aritomi, YaoChin, and Yuhang]
After the check of frequency-dependent squeezing(reported in elog 1805), we decide that we could go on the replacement of the Faraday isolator.
But we decide that we should do the replacement after measuring again frequency-independent squeezing. So we did the thing we report here.
The measurement of squeezing is done with the main laser not locked to the filter cavity. And the result is attached in the first attached figure. As you can see from this figure, we could only see a bit squeezing in the high-frequency region. At the same time, we found the CC1 loop was quite unstable. So we guess the phase noise is quite high now.
So we did the measurement of phase noise. The pk-pk value of CC1/2 phase noise is as following
| pk-pk | calibration factor | |
| CC1 | 40mV | pi/4/0.04/15 |
| CC2 | 208mV | pi/2/0.079/15 |
The result is attached in figure 2. By comparing the phase noise measured before and reported in elog 1572, they are quite similar. By comparing the shape of phase noise and squeezing measurement, we also found that CC2 phase noise is dominating the measurement of squeezing.
[Yuhang, Yao-Chin]
When dithering loop was open, we recorded that IR transmission modes correspond to AOM frequency (entry 1701) without parametric amplification of BAB which power was 318 uW. The result was as follows, mode matching was around 89.9%. We could realign suspension of BS and INPUT mirrors to reduce high-order modes. After aligning mirrors and dithering loop was closed, IR transmission was 405. At same time, we observed the GR and IR transmission signals during ten minutes as shown Fig 2. After ten minutes, IR and GR were misaligned obviously with decreased 16% and 4%, respectively. The CCD camera image changed from Fig 3 to Fig 4. Today, the filter cavity was unstable.
| Mode | IR transmission (average value) | AOM frequency (MHz) | Difference -109.03565 (MHz) |
| HG00(TEM00) | 370 | 109.03565 | 0 |
| HG10 (Yaw) | 115 | 109.43133 | 0.39568 |
| HG01 (Pitch) | 100 | 109.43223 | 0.39658 |
| HG11 | 98 | 109.82843 | 0.79278 |
| HG02 | 96 | 109.82922 | 0.79357 |
| HG20 | 97 | 109.83783 | 0.80218 |
| Background | 95 |
Note: From CCD camera image showed to define mode as Fig 1.
We measured the polarization map on TAMA #1 with different input polarization angles. 0 degrees represents the pure P polarization.
As can be seen, the S- and P- polarized map show apparent offset, which mainly due to the birefringence effect. In contrast, another three mixture maps show consistency with the input polarization angle.
[Aritomi, Yuhang, Yaochin]
First we checked IR mode matching again. Mode matching is 92% as follows.
| Mode | IR transmission |
| TEM00 | 365 |
| yaw | 112 |
| pitch | 98 |
| offset | 94 |
Then we measured frequency dependent squeezing around 50 kHz and 500 Hz (Pic. 1,2). CC2 demodulation phase is 75 deg for squeezing and 110 deg for anti squeezing. During this measurement, turbo pump was off and locking accuracy should be 3.1 Hz which corresponds to 3.3 pm (entry 1797). Pic. 3 shows squeezing degradation budget with current parameters.
Squeezing level inside filter cavity with 50 kHz detuning may be better due to better alignment. For FDS spectrum with 500 Hz detuning, we could observe squeezing angle rotation, but there is large phase noise below 100 Hz.
As we know, we need to align the filter cavity quite often. Sometimes we need to align many times during one day, sometimes it is stable for one day.
I took the alignment condition in the scale of the day (during October) and made this plot. We could use this as a reference for the alignment. We could have a feeling about how our filter cavity drifts for several weeks.
I worked on alignment for double-pass AOM with scanning frequency.
Since I have not prepared QPD yet, I used beam profiler to monitor the beam position.
Still the double-passed beam has beam jitter and need more optimization.
It should be noted that the input inpedance of frequency tuning is 1kOhm so that the actual input voltage from function generator which output inpedance is 50Ohm is doubled.
Tunable frequency range is 50-100MHz and it corresponds to +1.5 to +15V (+0.75V to +7.5V on display).
The attached is SMC connector to input voltage for frequency tuning.
| Mode | IR transmission |
| TEM00 | 3000 |
| yaw | 200 |
| IG20 | 140 |
| offset | 94 |
After this measurement, I checked mode matching without parametric amplification. Though IG20 was too small to be measured, mode matching was 96%.
| Mode | IR transmission |
| TEM00 | 390 |
| yaw | 100 |
| pitch | 100 |
| IG20 | - |
| offset | 94 |
Shoda, YaoChin and Yuhang
After the recovery of top coil(H1) of input mirror, we could use total four magnets to drive the length of filter cavity. Following the method of entry 1708, we calculated a driving index for input mirror. However, up to now, all the index is decided by the decouple of length/pitch/yaw at 4Hz.
The driving index is as following now
| H1 | 0.79 |
| H2 | 1 |
| H3 | 1 |
| H4 | 0.73 |
However, we could see from the following figure. We still have coupling at other frequencies.
A filter improvement (suggested by Matteo B.) has been implemented for PR pitch. I also added some notch at the frequency of the main lines.
Pic 1 comparison of the filters zpk
Pic 2 performances of the new filter
It seems to work very well.
First I checked IR alignment and found that IR TEM00 transmission was small. So I tweaked steering mirrors for IR injection and could recover the good alignment. Mode matching is around 95%.
| Mode | IR transmission |
| TEM00 | 385 |
| pitch | 110 |
| IG20 | - |
| offset | 94 |
Then we measured locking accuracy again as entry 1769.
We measured the Polarization map on TAMA#1 with different polarization angles. O degrees represents the pure P- polarization map.
As can be seen, these images show the same pattern in structure. Also the S- and P- polarization both show an apparent offset, which is most likely due to the birefringence effect.
[Aritomi, Matteo, Eleonora, Takahashi]
Yesterday we opened the input chamber with the help of Takahashi-san, and we confirm the intermediate mass was touching and picomotors were at the end range. (See entry #1783)
We adjusted IM mass and moved the picomotors by hand (and josystic) to make the reflection from the input mirror to superpose with the incoming one. It was quite hard to achive the superposition as we didn't notice that the intemediate mass was touching again and the picomotors couldn't move the mirror properly. Also the gatevalve between input and BS distorts the beam and causes multiple reflection.
Pic 1 and 2 show the current position of picomotors. In the pitch case we are quite close to the end of the range.
Today, since the vacuum was restored, we open the gatevalves and we could realign and lock the cavity again.
Anyway we found that the spectrum of the pitch motion has a large, sharp peak at 9 Hz that was not there before (pic3) . The TF seems fine (pic4). I wonder if there is still a problem with IM mass. As a first step I will try to adjust the control to damp it better.
Recently we switched off DDS board many times for the sake of avoiding RF signal cross-talk.
But recently every time we switch on again DDS, we heard a strange sound. From the sound, we guess the frequency seems to be a fixed audio frequency.
Up to now, our solution is
1. switch it off the rack containing the DDS board.
2. take out DDS3 board
3. switch on the rack
4. Put back DDS3 board while the power is on
By following this procedure, we could avoid the sound problem. But we still don't know what is the reason for this sound.
[Yao-Chin, Aritomi]
Testing method was same as entry 1785. However, we changed laser source to infrared light of 1064 nm. Infrared light hit in the first quarter of QPD2 (QPD2 input 1). We connected the corresponding DC output to the oscilloscope to check DC voltage. We also connected the corresponding RF output to a 32 dB amplifier and then check its power spectrum by a spectrum analyzer (Keysight N9320B).
We measured the light power, DC voltage, DC current by using "PuTTY", and RF channel power spectrum with RBW of 1MHz and average 28 times shown in pic. 1. Dark noise of pic.1 included the 32 dB amplifier and instrument when no IR light hit to QPD. In this measurement, when light power goes up, power loss is going down unlike the measurement in entry 1785. Green power in entry 1785 was too much since maximum DC current is 10mA according to specification and calculated DC current is already more than 10mA with 53.5 mW of green.
Pic. 2 shows same measurement in NIKHEF. The result is similar to our result, but we have some peaks around 25MHz, 125MHz, 140MHz.
|
Light Power [mW] |
DC Voltage [mV] |
DC Current [mA] |
calculated DC current (mA) (photosensitivity is 0.55A/W according to specification) |
power loss (%) (ratio of measured DC current/calculated DC current) |
| 0.58 | 248 | 0 | 0.319 | 100 |
| 1.25 | 504 | 0.1 | 0.688 | 85 |
| 2.5 | 1000 | 0.6 | 1.38 | 57 |
| 3.7 | 1500 | 1.1 | 2.04 | 46 |
| 4.5 | 1940 | 1.5 | 2.48 | 40 |
| 7.3 | 3000 | 2.7 | 4.02 | 33 |
| 9.5 | 4000 | 3.7 | 5.23 | 29 |
| 11.7 | 5000 | 4.8 | 6.44 | 25 |
| 13.5 | 5960 | 5.7 | 7.43 | 23 |
| 15.5 | 7040 | 6.8 | 8.53 | 20 |
| 17 | 8000 | 7.7 | 9.35 | 18 |
Today we reconfigured the setup to birefringence measurement. First, we measured the reflectance and transmittance under different conditions.
With the P-pol input polarization, we got
P_in = 7.64 mW, P_refl = 7.559 mW, P_trans = 0.206 mW
R = 0.9894, T = 0.0270
With the S-pol input polarization, we got
P_in = 7.649 mW, P_refl = 7.602 mW, P_trans = 0.007 mW
R = 0.9939, T = 0.0009
Then, we did the S-polarization map on TAMA#1. The result will be shown tomorrow.
We reconfigured the PCI system and measured the absorption map of the OSTM sample with ATC coating.
As can be seen, the figure shows a large value of absorption. And there are many spots with absorption excesses. Most likely, they are due to defects of the coating
[Yao-Chin, Yuhang]
Frequency from DDS with -6.5dBm sent to input LO & RF ports of demodulator (ZFMIQ-70D). The demodulator output I & Q ports connected low pass filter of DC-2.5MHz. We measured the Vpp and phase difference of I & Q ports from oscilloscope.
Note: Unbalance Amplitude (dB)= 20* log (Vpp of I port/ Vpp of Q port)
(I) Fixed LO port frequency of 78 MHz
(II) Fixed difference frequency of 100 Hz between LO and RF ports tune range from 66 to 80 MHz.
|
LO
(MHz)
|
RF
(MHz)
|
Vpp of I
(mV)
|
Vpp of Q
(mV)
|
Unbalance Amplitude
(dB)
|
Phase Difference btw I&Q
(degree)
|
|
66.0001
|
66
|
260
|
260
|
0
|
91.2
|
|
67.0001
|
67
|
262
|
260
|
0.07
|
90.1
|
|
68.0001
|
68
|
266
|
260
|
0.20
|
90.9
|
|
69.0001
|
69
|
266
|
260
|
0.20
|
90.6
|
|
70.0001
|
70
|
270
|
260
|
0.33
|
90.7
|
|
71.0001
|
71
|
272
|
260
|
0.39
|
90.9
|
|
72.0001
|
72
|
274
|
260
|
0.46
|
90.9
|
|
73.0001
|
73
|
276
|
259
|
0.55
|
90.6
|
|
74.0001
|
74
|
278
|
258
|
0.65
|
89.8
|
|
75.0001
|
75
|
281
|
258
|
0.74
|
90.2
|
|
76.0001
|
76
|
282
|
258
|
0.77
|
90.2
|
|
77.0001
|
77
|
282
|
255
|
0.87
|
90.6
|
|
78.0001
|
78
|
286
|
254
|
1.03
|
90.4
|
|
79.0001
|
79
|
286
|
254
|
1.03
|
90.1
|
|
80.0001
|
80
|
286
|
251
|
1.13
|
90.9
|
* Phase: Q=I+90o for LO>RF, Q=I-90o for LO<RF
To have an idea about how PD responses (at RF frequency) to green light. We did this test.
The test set-up is as shown in the attached figure 1 and 2. We put a periscope after the first green FI. It brings the green beam up to the second layer of the bench. At the second layer, we put a lens and a steering mirror to make sure the light is small enough and hit in the first quarter of QPD2. We connected the corresponding DC channel to the oscilloscope to check the output voltage DC. We also connect the corresponding RF channel to a 32dB amplifier and then a spectrum analyzer(Keysight N9320B) to check its noise spectrum.
To avoid any modulation and even RF cross-talk, we turned off the DDS system. The green power is changed by moving the offset of high voltage driver(connect to the PZT of SHG). We checked this offset is stable enough so that the green power doesn't change larger than 4% within the time of one measurement.
Within one measurement, we measured the light power/output voltage DC/output current(measured by using the 'putty')/RF channel spectrum.
| Output voltage DC(V) | Light power(mW) | Output current(mA) |
Calculated current(mA) (photosensitivity is 0.2A/W according to specification) |
power loss (%) (inferred from measured and calculated current) |
|---|---|---|---|---|
| 5.6 | 34.5 | 5.3 | 6.9 | 23.2 |
| 7.7 | 53.5 | 7.4 | 10.7 | 30.8 |
| 8.8 | 70 | 8.7 | 14 | 37.9 |
| 10 | 90 | 10 | 18 | 44 |
The relation between power and voltage/current is attached in figure 4.
I also calculated the shot noise by using this formula: shot noise = 10*log((sqrt(2*1.6e-19*I)*sqrt(RBW))**2*35/1mW)+32+22, then I got the calculated shot noise level
| Output Voltage DC(V) | Calculated shot noise(dBm) |
|---|---|
| 5.6 | -48.3 |
| 7.7 | -46.8 |
| 8.8 | -46.1 |
| 10 | -45.5 |
While the measured shot noise is attached in figure 3, which shows -60dBm for all different light power.
