I checked REFL51 and REFL135 dark offsets at several different timing (fig1:10/30, fig2:10/29, fig3:10/25).
Small jump can be seen in REFL51I signals but there seems no jump in the others.
Also, the jump is not so large compared to the drift.
So, it is likely that the dark offset change was due to the drift of the offset.

We measued TFs from PDA1_RF45_I_ERR and CARM_SERVO_MIXER_DAQ_OUT which are in-loop sensors for CARM to the DARM displacement (CAL-CS_PROC_DARM_DISPLACEMENT), and also measured the TF from PDA3_RF45_I_ERR, which is an out-loop sensor for CARM to the DARM displacement when we excited CARM from CARM_SERVO_EXC_A_CALI. Fig.1 shows the results. (Note that, the unit of the TF from MIXER_DAQ_OUT to DARM is m/V, the others' unit is m/cnt).

Then, we projected the current spectra of MIXER_DAQ_OUT as the in-loop sensor and PDA3_RF45_I_ERR as the out-loop sensor in DARM sensitivity by using each TF. Fig.2 shows each projection, magenta is the projection from MIXER_DAQ_OUT, green is from PDA3_RF45_I_ERR. According to the magenta line, the current in-loop CARM noise seems not to limit the current sensitivity. Unfortunately, the current PDA3 output in high frequency region seems to be dominate by the other noise due to the low input power to PDA3.

Next, we projected the sensing noises of MIXER_DAQ_OUT and PDA3_RF45_I_ERR. We picked up each raw sensing noise spectrum which were measured by Ushiba-san (see the detail in klog31636) in /users/Commissioning/data/CARM/2024/1114/SPE_CARM-20dB_CMS_sensingnoise.xml. Fig. 3 shows the projected sensing noises using each TF, the orange line is the sensing noise of MIXER_DAQ. Then, I tried to compensated roughly the input power difference between the orange and the magenta. The input power when the orange was measured was 2988 cnts, and the power when the magenta was measured was 846 cnts. So I assumed this orange sensing noise is only shot noise (honestly, orange line seems to have a shape so this assumption is overspeaking), and devided the orange line by (2988/846)^(1/2) ~ 3^(1/2). The black line is divied one. If the current sensing noise is only shot noise, the current CARM noise is limited by the sensing noise. 

Could you please explain Fig.4? It shows the reduction of displacement.

>Even the OMC resonance peak happens to align with the peak of the lock loss blast, the energy deposited on OMC PDs (total of two PDs) for 10 W input will be
>10 * 19 W * 50 usec = 9.5 mJ

If we consider the speed of scan (5ms), OMC psses on the resonance 3 times within FWHM (15ms).
Even in that case, obtained energy of PD is less than 9.5mJ * 3 = 28.5 mJ, which satisfy the requirement (< 30mJ).

Too consistent, isn't it...?

The lock loss blast with a peak height of 19 W and FWHM of 15 msec gives integrated energy of roughly 19 W * 15 msec = 0.3 J.
Intra cavity power with 1 W input for each arm is Pcav = Pin * PRG * 4/T_ITM / 2 = 1 W * 15 * 4/0.4% / 2 = 7.5 kW.
This means that total energy stored in XY arms is Ecav*2 = Pcav * 2 * 2 * Larm / c = 0.3 J.
Amazingly consistent (see also JGW-T2416173).
To have less than 30 mJ at OMC PDs (total of two PDs) when the input power is 10 W, we need to reduce the OMC duty factor to less than 30 mJ / (0.3 J * 10) = 1%.
Continuously sweeping OMC with a triangular wave of peak-to-peak of 1 FSR gives (effective) duty factor of 1/Finesse = 1/800 = 0.125%.
So, sweep of 0.125 FSR peak-to-peak would be enough.
Using 100 Hz triangular wave, time to sweep the OMC resonance peak will be
1 / 100 Hz / 2 * (1/Finesse) / 0.125 = 50 usec
Even the OMC resonance peak happens to align with the peak of the lock loss blast, the energy deposited on OMC PDs (total of two PDs) for 10 W input will be
10 * 19 W * 50 usec = 9.5 mJ
This is smaller than the 30 mJ requirement. So, sweeping with 0.125 FSR peak-to-peak at 100 Hz will be good.

I changed the setpoint of the heater from 26.0° to 25.0° at 9:26 JST.

I checked the signals last night and confirmed that OMMT2T trans DC PD was not saturated when lockloss happened.
Figure 1-3 shows the signals when the lockloss happened in this morning.
The first peak power is about 19W and the second is about 4W (fig1).
FWHM of the first peak and second is about 15ms (fig2) and 5ms (fig3), respectively.

After achieving PRFPMI_RF_LOCKED, maximum power at AS is about 500mW (fig4), so if we set the power treshold at AS as 1W or something, the trigger seems to work only when lockloss happens.
In addition, speed of power increase from 1W to 19W is about 20ms (fig5).

Before this work, I checked the Pcal-X beam positions on the ETMX, and adjusted a little.
What I used are PCAL_EX2 picos.

Pico movment: 

• PCAL_EX2 pico 1: +50
• PCAL_EX2 pico 2: +100
• PCAL_EX2 pico 4: +50

Beam positions on the ETMX changed by about 2mm:
Before ([0,0] means the design position.): Fig 1 = TCam_ETMX_00111_2024_1120_051540_fitting_comp.png

• Pcal beam position (path1) [mm]: [3.91584, 2.40329]
• Pcal beam position (path2) [mm]: [2.75383, 3.67881]

After: Fig 2 = TCam_ETMX_00111_2024_1120_054412_fitting_comp.png

• Pcal beam position (path1) [mm]:  [3.98096, -0.55771]
• Pcal beam position (path2) [mm]:  [2.67615, 1.67651]

During calibration at the end station, we found the beams were slightly(2-3mm) shifted from the centre on the RxPD.
Today, we proceeded the calibration without making the adjustment. The impact on the calibration results appears to be limited, but it may need to be adjusted in the future.

Yokozawa, Michimura, Ushiba, Tanaka

This morning, Yokozawa-san found PRMI kicked when its 3f lock acquisition. We found that the phasing of RF51 seemed to be bad when the demod. phase value was 60 deg. So we rotated the phase to maximize the Q output when we excited MICH. The value after the rotation was 145 deg.

Next, HANDOVER from ALS to IR got hard because the glitch in MICH error signal when IR beam flashed in the arm cavity became large. This issue is the same as the one in klog30912. So we need to make the demod. phase worse in order to reduce the glitch

On the other hand, Michimura-san found that the RF51 and RF135 signals had dark offsets (~ several cnts). We subtracted them (fig.1) and then, the PRMI could locked smoothly even though the demod. phase of RF51 was 60 deg. HANDOVER also succeeded with this demod. phase. 

## NOTE

I also subtracted the dark offset of AS_PDA1_RF17_{I,Q}, REFL_PDA1_RF45_{I,Q}, POP_PDA1_RF{17,45}_{I,Q}, POP_PDA2_RF90_{I,Q} manually.

[Tanaka, Ushiba]

We reduced OMMT2T PDA1 gain from 70dB to 30dB.
After that, dark noise was measured and subtracted (fig1 shows the signals when IMC was locked).
Also, calibration factor was increased by a factor of 100.

With Michimura

We performed the integrating shpere calibraiton for Pcal-X.
The results are similar to the previous measurements.

Result Summary:

Alpha values are voltage ratio between ISs in XPcal and WSK. 
alpha_RxPDpWSK_1 = 1.01099 +- 0.00028
alpha_RxPDpWSK_2 = 1.00658 +- 0.00034
alpha_TxPD1pWSK = 2.84929 +- 0.00030
alpha_TxPD2pWSK = 3.88791 +- 0.00037

e values are optical efficiency values. 
e_1 = 0.96496 +- 0.00020
e_2 = 0.95479 +- 0.00023

Abstract:

Power at AS can reach more than 4W even with 1W operation when the lockloss happens.
Due to the saturation, it is difficult to confirm how much power is going to AS when lockloss happens.

Detail:

To estimate the power at AS when lockloss happens, I calibrated K1:LSC-AS_PDA1_DC_OUT_DQ to OMC transmission.
Figure 1 shows the signals when OMC was locked with single XARM lock.
When OMC transmission was about 35.7mW, the value of K1:LSC-AS_PDA1_DC_OUT_DQ was 0.055, so the calibration factor from K1:LSC-AS_PDA1_DC_OUT_DQ to the power at OMC is 650 mW/cnt.

Figure 2 shows an example of lockloss with 1W operation.
It takes 20ms to increase the signals at AS from 0.2 to 6.2 (saturation), which are corresponding to 130mW and 4W.
After saturation, signals keep more than 6.2 cnts for 17.5ms but I'm not so sure the power to OMC keeps morethan 4W for 17.5ms because the signals had already saturated.

Since current PD gains at OMMT2T and POS are too high and they saturate before the saturation of AS PDs, it is necessary to reduce the PD gain to confirm the real trend of AS power.