Measurement of current loss budget

Aritomi, Eleonora, Yao-Chin, and Yuhang

We summarized the loss budget in the first attached figure.

From the power measurement as following, we could know this part contributes about 10% of loss

measured after first PBS after OPO	265uW
measured after last mirror before PR chamber	198uW

From the power measurement as following, we could know this part contributes about 1% of loss

measurement of IR reflection after PR chamber	221uW
measured before homodyne	218uW

We also measured the IR reflection(IR_ref) beam shape as in the attached figure 2. It has a bit ellipse in the horizontal direction. Because of this elongation, we had a second order peak when we match this IR_ref to alignment mode cleaner(as shown in the attached figure 3,4). By comparing this higher-order peak(12mV) and TEM00 peak(276mV), we could deduce the homodyne readout efficiency should be (1-12/276)^2 = 91.5%. But this IR_ref has beam jittering, so the real readout efficiency should be less than 91.5%.

We also measured the filter cavity round trip loss again. By using the same method we used last year, we found now this value is around 100ppm. We will do more investigation to make sure of this. The measurement is attached in the figure 5. 

In the last figure, the achievable squeezing without considering phase noise is attached.

Saturation of CC2 correction signal

[Aritomi, Yuhang, Yaochin, Eleonora]

We have saturation of CC2 correction signal (8Vpp) and it seems coming from servo since we have this saturation without connecting piezo. HV amplifier we are using can take up to 10V and the gain is 30 and piezo for phase shifter can take up to 1000V.  So we are using 240V out of 1000V piezo range.

Frequency dependent squeezing at 50kHz

[Aritomi, Yuhang, Yaochin, Eleonora]

Today we measured frequency dependent squeezing at 50kHz.

Setting is same as yesterday (AOM frequency is 109.13698MHz). Since CC2 lock is unstable, we made average number 5 while it was 50 yesterday.

Frequency dependent anti squeezing at 50kHz

[Aritomi, Yuhang, Yaochin, Eleonora]

Today we measured frequency dependent anti squeezing at 50kHz.

We set AOM frequency 109.13684 MHz which is larger than carrier frequency by 100kHz and corresponds to 50kHz detuning. CC2 demodulation phase is 105deg for squeezing, 155deg for anti squeezing and 135deg for intermediate.

Power measurement when PR chamber is open(measured on 20191011)

Aritomi, Matteo, Yao-Chin, and Yuhang

All the measurement is inside PR chamber. We sent BAB to do this measurement.

injection power	394uW
before dichroic	379uW
after dichroic	375uW
transmission from the first PBS	3.4uW
transmission from the second PBS	3uW
before going back to bench	334uW

Injection loss: 4.8%

Reflection loss: 10.9%

IR reflected from filter cavity cut issue solved

Aritomi, Matteo, Yao-Chin, and Yuhang

We opened the PR chamber on last Friday. But moving the last IR back reflection steering mirror, we solved the cut issue of this beam.

Attached figure 1: We just opened PR chamber, we checked with IR viewer. We could see a beam on the right side of chamber window.

Attached figure 2: After moving the last IR back reflection steering mirror, we made IR back reflection hitting on the window. And this IR back reflection is between IR(injection) and GR.

H1 INPUT mirror coil doesn't respond but coil driver is fine

Yesterday I investigated the issue of not responding coil of INPUT mirror.

I made some tests by swapping the coil driver channels and I concluded that the coil driver is working fine and the problem is inside the vacuum chamber.

The not responding coil is H1 (top coil). This unbalance in the pitch driving will excite length. This can be maybe counteracted with horizontal coils. 

We should consider if to open the chamber for further investigation/coil repairing. 

Set of iris on IR reflection path for tomorrow's chamber open

Yaochin and Yuhang

Since we will open the chamber tomorrow and move the last IR reflection steering mirror in-vacuum.

To define the beam reflection direction, we think we should check two points. The first point has put an iris. The second point is homodyne PD.

We will use these two points as a reference and then move the mirror.

Set of PD at the window of PR chamber

Aritomi. Yaochin and Yuhang

We set two PDs outside the PR chamber(attached figure 1), where we have the reference of two IR beams and two GR beams. The set two PDs are used to monitor two IR beams.

Mainly they have two functions:

1. Monitor the power (leakage from PBS before and after in-vacuum FI) injected into the filter cavity. Since we have the problem of IR transmission fluctuation, we want to see if this fluctuation also presents in the input beam. The problem can be found in this entry 1710. We just temporarily monitor this leakage power and the result is shown in the attached figure 2.

2. Use as a reference for the adjustment of in-vacuum FI.

The measurement of NIKHEF PD amplifier gain

Eleonora and Yuhang

Since we have the measurement of qubig PD and NIKHEF PD reported in entry 1728 we could use the measurement result to compute the NIKHEF amplifier gain. The signal transfer is like following:

qubig PD:       PDH signal pk-pk (164mV) = laser power (0.21mW) * photosensitivity (0.27 A/W) * amplifier gain (16e3 V/A) * RF amplification (14dB) * mixer gain * lowpass filter gain

NIKHEF PD:  PDH signal pk-pk (14.8mV) = laser power (1.2mW) * photosensitivity (0.2 A/W) * amplifier gain (we want to know V/A) *  RF amplification (14dB) * mixer gain * lowpass filter gain

Since we are using the same RF amplifier, mixer and lowpass filter, and we know the gain and photo-sensitivity of the quibig PD (16 kV/A) we could calculate the amplifier gain of NIKHEF PD:  ~ 340 V/A(50dB).

We shoud check if this is consistent with the calculation from the electronic schematics. If this is the case we conclude that the Nikhef quadrant has no problem but its gain is too small to be used without amplification.

Record IR and GR laser light height

[Yao-Chin, Yuhang]

We record GR & IR height before the light is sent into chamber window.
Pic. 1 shows the GR height of 76 mm and its beam size of 4 mm. Pic. 2&3 observed by infrared viewer show IR height of 76 mm and 75.5 mm. The observed position of Pic 2 is relatively close to chamber window than Pic 3.

Tuning of binary number of CC PLL and CC1 demodulation frequency (CCFC)

[Matteo, Aritomi]

Yesterday we found low frequency oscillation of CC2 error signal and tuned frequency of CC PLL and CC1,2 demodulation frequency to remove this, but we found that binary number of these frequencies were different. Frequency difference between CC PLL and CC2 demodulation was actually 0.04Hz and this may cause low frequency oscillation of CC2 error signal. Then we tuned binary number of CC PLL and CC1 demodulation frequency. Current setting is as follows. I attached the pictures to be sure. Note that CC PLL frequency is divided by 3 at PLL board.

channel	function	frequency (MHz)	binary number
CH0	CC PLL	20.99099988	1010101111110101010100010100
CH2	CC1 demod	13.99399992	111001010100011100010111000
CH3	CC2 demod	6.99699996	11100101010001110001011100

 

 

 

 

We'll check CC2 error signal and AOM frequency of CCSB next week.

Check of IR alignment

Current mode matching is 92% and should be fine.

Mode	IR transmission
TEM00	1500
HG01 (pitch)	180
IG20	130
offset	94

Polarization Maps on Sapphire Samples from SHINKOSHA #S1, #S2, #S3, #S5, #S6

[Simon, Pengbo]

Attach to this report are the polarization maps and polarization angle distribution maps.

As can be seen, the polarization maps of these five samples both very homogeneous.

Recent setting of OPO temperature and p pol PLL

green power (mW)	OPO temperature (kOhm)	p pol PLL (MHz)
0		305
40	7.19	165
60	7.2	150

OSTM coating absorption

Pengbo, Simon

Attached are the figures summarizing the results on the absorption measurment of OSTM's coating (-> Sigma Koki).

As can be seen, there are many spots with absorption excesses. Most likely, they are due to defects of the coating. Other than that, the absoprtion is quite homogenous with a mean value of 16 ppm.

Measurement of IR power loss from two PBS before and after the in-vacuum FI

We have two reference points for IR injection to filter cavity(FC). They are from the two PBS before and after the in-vacuum FI. And this will be also a loss for squeezing in the future. Also, if we want to monitor the power we are injecting to FC, this can be a choice of checking point.

So we measured the power arriving at these two points. 

power loss from PBS before in-vacuum FI (first PBS)	0.59uW	attached photo 1	so the polarization before PR chamber is optimized better
power loss from PBS after in-vacuum FI (second PBS)	2.78uW	attached photo 2	so the polarization before the second PBS is not optimized very well

We could optimize the HWF after the in-vacuum rotator, but we will lose some isolation factor.

Actually, Matteo said maybe we can have the choice to optimize the Faraday rotator, if so, our maximization of IR reflection should be done by optimizing the Faraday rotator.

PDH signal comparison from FC reflection(qubig PD and NIKHEF PD)

To compare the signal from qubig PD and NIKHEF PD, I did this check. (There was already a check reported in the entry 1670)

The situation of green power is

green power on qubig PD	210uW
green power on NIKHEF PD	1.2mW

The electronics after PD is

1. qubig PD	then goes to RFamplifier(14dB)	then goes to demodulator (used for FC locking, from the mini-circuit company)	then detect on the oscilloscope	----------
2. NIKHEF PD (I put all light on the first quarter of this PD on purpose)	then I take the RF signal from the first quarter	then goes to RF amplifier(14dB)	then goes to demodulator (used for FC locking, from the mini-circuit company)	then detect on the oscilloscope

The result of PDH signal is

qubig PD pk-pk	164mV	attached Fig.1
NIKHEF PD pk-pk	14.8mV	attached Fig.2

Note: If I put these signal to NIKHEF demodulator is qubig PD pk-pk 35mV(reduce by a factor of ~5), NIKHEF PD pk-pk 10mV(reduce by a factor ~1.5).

Frequency tuning of coherent control sidebands (CCFC)

[Aritomi, Yuhang, Yaochin]

We could see transmission of both coherent control sidebands (CCSB) from filter cavity at CCD camera with 40mW green. Pic.1 shows upper CCSB transmission at camera. We found that when CC PLL frequency is 7MHz, AOM frequency of upper CCSB is 109.04179MHz and lower CCSB is 109.02990MHz while AOM frequency of carrier is around 109.036 MHz. In CC locking of filter cavity, either of CCSB is on resonance and other CCSB should be separated by ~100Hz. So we tuned CC PLL frequency in order to have ~100Hz of CCSB separation frequency. Note that AOM frequency separation corresponds to twice of CC frequency separation.

CC PLL frequency (MHz)	AOM frequency of upper sideband (MHz)	AOM frequency of lower sideband (MHz)	CC frequency separation (Hz)
7	109.04179	109.02990	5940
6.997	109.03608	109.03599	45
6.9967	109.03665	109.03528	685
6.9963	109.03728	109.03461	1335
6.995	109.03991	109.03189	4010 4010
6.993	109.04322	109.02855	7335

Frequency separation with 6.997MHz of CC PLL is close to frequency separation that we want, but AOM frequency with 6.997MHz of CC PLL is not so precise since CC transmission seems not changing at camera around this region and we couldn't distinguish upper and lower sideband.

Pic. 3 shows plot of CC PLL frequency and CC frequency separation. The fitting result is

CC frequency separation (Hz) = -1907605 * CC PLL frequency (MHz) + 13347486

If you want to have 108 Hz of CC frequency separation, CC PLL frequency should be 6.996930 MHz or 6.997043 MHz.

After we set CC PLL 6.997MHz, we found that CC1,2 error signal oscillated since demodulation frequency of CC1,2 was not tuned. After we set demodulation frequency of CC1 6.997*2=13.994MHz and demodulation frequency of CC2 6.997MHz, the oscillation dissappeared and we could lock CC1,2. However, when we open the CC2 loop, CC2 error signal has low frequency oscillation (Pic. 2) due to residual frequency difference between CC PLL and demodulation phase and it is difficult to remove.

Phase noise with/without feedback to INPUT mirror

Aritomi, Yaochin and Yuhang

After we feedback CC2 correction to INPUT mirror, we calculated the phase noise. The result is shown in entry 1719. But when we compare this result to entry 1614, we found after feed it back to INPUT, the acuumulated RMS is even higher.

Actually, if we look into the detail, the main difference comes from basically high frequency region (kHz to 100kHz). Personally, I have the impression the phase noise is different sometimes. For example,  in entry 1522, we reported phase noise reduce after long time laser on. But for example, today(we kept laser on also for several days), the phase noise is a bit higher and we couldn't even lock CC2 loop(we could lock one month ago).

So it is important to compare the high frequency region of phase noise with/without feedback to INPUT mirror. We did this measurement with filter cavity unlock. Because we have some issue with the CC2 loop error signal(Aritomi-san may report later), so the comparison is not calibrated to the unit of [rad].

The comparison is only in high frequency region because we could lock CC2 only for very short time when there is only feedback to CC2 phase shifter PZT. But at least from this measurement, high frequency is not affected whether we feedback to INPUT mirror or not.