KAGRA Logbook

Cont'd work

Actuator efficiency of BS TM
Now we have MICH optical gain, Hc, by Michelson fringes just before and after the measurement of MICH open loop transfer function in klog#24969. (Hc = 1.0893e9)
By using Hc as a standard of the calibration, actuator efficiency of BS TM, Ha, can be estimated from OLTF in short Michelson lock.
Measured and model OLTF and residual of measurement and model are shown in Fig.1 and Fig.2, respectively.
Estimated Ha is (5.238 +/- 0.074) * 1e-11 / f^2. This is 12% different from previous estimated value (5.9e-13 / f^2).
Note that this value is MICH_L basis. So actuator efficiency in BS_L basis is sqrt(2) times smaller.

Actuator efficiency of ETMX TM
Actuator efficiency of ETMX can be estimated as
$H_{\rm etmx, tm} = (\rm ETMX/ITMX)_{\rm DARM} \times (\rm ITMX/BS)_{mich} \times H_{\rm bs, tm}^{\rm mich}$
= (0.04733 +/- 0.00020) * (1.2228 +/- 0.0029) * (5.238 +/- 0.074) * 1e-11 / f^2
= (3.031 +/- 0.045) * 1e-12 / f^2
This is ~14% change from previous estimated value based on Green AOM (3.524e-12 / f^2).

Actuator efficiency of PRM TM
In order to decide the actuator efficiency of PRM, we also measured the transfer functions from PRM and BS to PRCL error signals.
A ratio of these two TFs indicates a ratio of actuator efficiency of PRM and BS.
Figure 3 and 4 shows the measured TFs and ratio of them.
From these results, actuator efficiency ratio between PRM and BS is estimated as 27.39 +/- 0.26.

As shown in Fig.5, BS actuator efficiency in PRCL basis is 2 times smaller than one in MICH basis.
So we can compute PRM actuator efficiency in PRCL basis as
$H_{\rm prm,tm} = (\rm PRM/BS)_{\rm PRCL} \times \frac{1}{2}H_{bs,tm}^{mich}$
= (27.39 +/- 0.26) * 0.5 * (5.238 +/- 0.074) * 1e-11 / f^2
= (7.17 +/- 0.12) * 1e-10 / f^2
This is 30% different from klog#13020 (1.0e-9) and 4 times different from klog#14555 (2.96e-9).
Hmm...

Optical gains
Optical gain of DARM, PRCL, MICH in PRFPMI can be estimated from open loop transfer functions and actuator efficiency of ETMX, PRM and BS as
$H_c^{\rm dof} = G_{\rm meas.}^{\rm dof} / (C_{0, \rm model}^{\rm dof} D A_{\rm model}^{\rm optic})$

Measured and model OLTF and their residual are shown as Fig.6, 7 (DARM), Fig. 8, 9 (PRCL), Fig.10 and 11 (MICH) and estimated optical gains are as follows.
Hc_DARM = (7.67 +/- 0.11) * 1e12
Hc_PRCL = (1.533 +/- 0.026) * 1e7
Hc_MICH = (6.707 +/- 0.096) * 1e8