ELOG 40m

Transfer Function for IMC mirrors using appropriately filtered noise

that is great

I think we would like to set the WFS1 P/Y UGFs to be ~2-3 Hz, and the MC_TRANS loops to have a UGF of ~0.1 Hz.

Could you use your loop gain measurements to set the _GAIN values for those UGFs? I am curious to see if the system is stable with that control.

17489

Thu Mar 2 18:37:05 2023

Tomohiro

Transfer Function for IMC mirrors using appropriately filtered noise

Summary

Alex, Anchal, and I measure the open-loop transfer function for WFS and MC2_TRANS signal.
We utilize Fourier transform of appropriately filtered Gaussian noise to obtain the transfer function.
With appropriate frequency-dependant noise and appropriate overall gain, the transfer function at lower frequency around 1 Hz can be roughly measured in shorter time and with a narrower resolution than those of the swept sine.

Purpose

The purpose is to roughly measure the open-loop transfer function in shorter time and with a narrower resolution. The transfer function can usually be obtained the following process. We measure two points before (IN1) and after (IN2) the excitation signal injection point. We can get the transfer function by dividing IN1 signal by IN2 signal. However, this method has some difficulties: longer time to finish one measurement in lower frequency and less measuring points. These are because the frequency of excitation signal is fixed for every measuring point. The ordinary method is not suitable for rough measurement. Therefore, we try to utilize frequency-dependant noise for measuring the transfer function (Rana teaches us the method).

Method

We utilize the Gaussian noise instead of the fixed sine wave. We inject the noise, which is properly filtered, into the exciting point (such as C1:IOO-MC2_TRANS_YAW_EXC in C1IOO_WFS_MASTER window), and measure two signals in the points IN1 and IN2. The two signals are Fourier transformed. And we obtain the transfer function by dividing the transformed signal IN1 by that of IN2.

To get good SNR, the frequency dependence of the injecting noise signal is important. We use the awggui command to create the appropriately filtered noise. We decide the dependence from the coherence between the IN1 signal and the excitation signal. The coherence around 1 shows the good SNR. So the dependence is adjusted so that the coherence approaches 1 in the observation frequency range. Attachment 1 shows the frequency dependence of the filter. We cut the gain below 0.1 Hz and above 10 Hz to limit frequency range, and use Zero-Pole gain to treat the influence of the mirrors' suspension in the frequency range. The filter we used is

cheby1("BandPass", 6, 2, 0.1, 10)
zpk([3], [0.3], 1, "n")
zpk([0.375 + i*0.649519; 0.375 - i*0.649519], [0.75; 2.5 + i*14.7902; 2.5 - i*14.7902], 1, "n")gain(4.46889)
zpk([13], [3], 1, "n")gain(1.05099)

The file is saved in /users/Templates/MC/wfsTFs/WFS_noise_injection_profile-230302, but the saved file loses some filter information... So we write all the filters above.

Note: The noise filter has a ripple around the cutoff frequency. It comes from cheby1. Chebyshev Type 1 filter can drop the gain rapidly but has the ripple around the cutoff frequency.

Longer averaging time is also important to get the better SNR. The time is estimated from the resolution frequency and overwrap of the time-series data. We set the resolution as 0.01 Hz and the overwrap as 50 %, so the 10 times averaging takes about 8 minutes. In contrast, it takes about 2 hours if we measure 10 cycles of sine wave for every frequency with the ordinary transfer function measurement. The method of using the noise signal can inject multiple frequencies simultaneously into the excitation points, and can reduce the total measuring time.

We use the diaggui command for measuring the transfer function. Fourier Tools in Measurement tab translates the time-series signals, and the transfer function is obtained by Graph, Transfer function, in Result tab. Fig 2 is an example. The settings are saved, for example, in /users/Templates/MC/wfsTFs/MC2-TRANS_YAW_230302.xml.

In every measurement, we inject the noise into every excitation point of WFS1, 2 and MC2_TRANS, and PIT and YAW, and take every transfer function. We change overall gain of the filter in every measurement. The values are listed as follows.

Note: The gain of the transfer function is changed from 0.7 to 21 in the WFS1_PIT case only. The value of the case is much bigger than other measurements. After the experiment, the gain is put back.

WFS1	value	WFS2	value	MC2	value
PIT	1002345	PIT	152345	PIT	123456
YAW	52345	YAW	52345	YAW	183456

Result

We show some results (YAW of WFS1, 2, and MC2_TRANS) as an example. The MC2_TRANS_YAW data only has structures around 3 Hz and 7 Hz shown in Attachment 2. The coherence of all measurements in the frequency range [0.1 Hz, 10 Hz] is around 1 except for the pendulum frequency of IMC mirrors. All the results have similar trend, which is low-pass like frequency dependence and has resonant of the pendulum. The trend is also obtained in the previous measurement using the ordinary method such as 40m/17486 and 40m/17472.

Discussion

Phase margin result for every measurement is listed. MC2_PIT data is 'N/A' because the transfer function does not exceed 0 dB at the observation frequency range. The phase margin values except for WFS1_PIT case are small, that is, the servos are nearly unstable. In WFS1_PIT, the phase margin is larger than other data because we increase the overall gain of the loop from 0.7 to 21 during measurement. This indicates the overall gain of the loop should be increased.

WFS1	value	WFS2	value	MC2	value
PIT	40 deg	PIT	20 deg	PIT	N/A
YAW	10 deg	YAW	20 deg	YAW	20 deg

The pendulum resonance reduces the coherence. The coherence shows the signal relevance at the excitation point (input) and the measurement point (output). We can estimate whether the injecting signal is buried by background noise. The noise filter is not optimized yet, and we use the same filter for all the measurements. It causes the reduction of the coherence around the pendulum resonance. To increase the coherence and take better measurement, we have to optimize the frequency-dependance of the noise filter and increase averaging times for every measurement.

Only in the case of MC2_TRANS_YAW, the sudden gain changes exist around 3 Hz and 7 Hz. The sudden change is small peak at 3 Hz and large dip at 7 Hz. The result in 40m/5928 has a structure at 3 Hz, but we cannot find the structure at 7 Hz in the past entry... But both sudden changes do not make the loop unstable because the gain at the frequencies are smaller than 0 dB. We will check the detail and the origin.

In Future

The overall open-loop gain should be increased.
If necessary, we have to optimize the noise filter for every measurement.
If necessary, we will check the detail and the origin of the sudden gain changes around 3 Hz and 7 Hz in MC2_TRANS_YAW.

Attachment 1: NoiseFilter_TF.png

Attachment 2: TF-MeasureExample.png

Attachment 3: WFS1_YAW_OLTF_NI.png

Attachment 4: WFS2_YAW_OLTF_NI.png

17488

Thu Mar 2 10:54:25 2023

We added the DB9 short connectors to all coil drivers in the BHD suspensions and updated FM9-FM10 for LO1, LO2, AS1, AS4, SR2, PR2 and PR3 to match the work on LO1 yesterday. We then locked the LO phase using BH55 and took noise spectra for the error and control points; Attachment #1 shows the comparison before and after these changes were made.

Attachment 1: uncalibrated_lo_phase_errctrl_ADW.png

17487

Wed Mar 1 19:18:18 2023

[Paco, Anchal]

Today we invested some time in the DW filters for LO1 supension. We discovered that the binary DW enable/disable channels were not connected, and we had basically postponed testing this final bit on the chain of new SUS electronics since the upgrade took place. A quick noise spectrum of error and control points (uncalibrated) show that outside of the ~ 40 Hz control bandwidht, the LO phase noise rms is dominated by line noise (mostly 180 Hz) (Attachment #1).

We checked the BIO inputs, but failed to make them work from the c1su2 model and Anchal spotted an error in the model; so maybe to speed up the proper dewhitening tests, we override the acromag enabling BIO interface and just short the coil driver BI to always enable the Analog DW filter. Then, using the measured DW transfer function with z = [130 + 0j; 233+0j], p=[10+0j; 2845+0j], k=2.0, we corrected the FM9 and FM10 in the coil outputs (this is different from the other DW filters). Today we just did this for LO1, but the next step is to replicate this for the other BHD SOS so that we have a consistent test.

So for now, the LO1 coil drivers at 1Y0 have shorted binary inputs to enable watchdog + Analog dewhitening filters. This needs to happen on LO2, AS1 and AS4, and then the noise spectra should be measured again.

Attachment 1: uncalibrated_lo_phase_errctrl.png

17486

Wed Mar 1 17:13:38 2023

Transfer Function for IMC mirrors using sine sweep

The following work has been done by Tomohiro, Anchal and I:

To acquire the transfer functions for each of the IMC mirrors, we utilized diaggui, the CDS Diagnostic Test tool. We would like to measure the open loop transfer function, which is the ratio of In1 and In2, corresponding to before and after the injection point of the excitation signal.

A sinusoidal excitation signal was swept from 0,2 Hz to 5 Hz and includes 11 data points from an average of 10 cylcles per point.

NOTE: the WFS gain must be adjusted from 1.0 to 4.0 for these measurements (this is the slider underneath the "Turn WFS ON/OFF" button in C1:IOO_WFS_MASTER.

For the three sets of data taken for Pitch in WFS1, WFS2, and MC2 Trans, the amplitude of the excitation wave was 30,000.

In each measurement, the injection point is "C1:IOO-X_EXCMON", where X is the WFS or MC2 + Pitch or Yaw.

We will be conculding our measurements tomorrow and will report the findings for YAW in WFS1, WFS2, and MC Trans2.

Attachment 1: WFS1_PIT_OLTF.pdf

Attachment 2: WFS2_PIT_OLTF.pdf

Attachment 3: MC2_TRANS_PIT_OLTF.pdf

17485

Wed Mar 1 10:16:31 2023

Tomohiro

Angular actuation calibration for IMC mirrors using AC sine wave

Alex, Anchal, and I did the following experiment to obtain calibration constants by oscillating IMC mirrors.

Theory

In previous experiment, we measured transmission counts at some offset values, and fitted the curve in order to get the curvature of transmitted power at MC2. In this time, we use not offset but AC oscillation to get the curvature $\gamma$ .

The shape of the transmitted power is quadratic with respect to the tilt of each mirror:

$y = a_0 + a_1 x + a_2 x^2.$

Here $x$ is the parameter including the tilt of each mirror, and $y$ is the signal of the transmitted power at MC2. Oscillating the mirror shows that $x$ has a time-dependance $x = A_0 \cos (\omega t + \phi_0)$ using an angular frequency $\omega$ , an initial phase $\phi_0$ , and an amplitude $A_0$ . What we want to get is the curvature of the quadratic function, that is, the coefficient $a_2$ . So we focus on the frequency-doubled term. By substituting $x(t)$ to $y$ , we get the time-dependent $y$

$y(t) = \left( a_0 + \frac{a_2}{2} {A_0}^2 \right) + a_1 A_0 \cos(\omega t + \phi_0) + \frac{a_2}{2} {A_0}^2 \cos( 2\omega t + \phi_0)$ .

We can get $a_2$ value as $a_2 {A_0}^2 / 4$ by multipling $\cos(2 \omega t + \phi_0)$ and taking time average. This $a_2$ is the same as $\gamma$ used in 16125 by Anchal when the unit of $x$ is cts.

Method

Before the experiment, we changed some settings

Turn off servo in the WFS servo,
Turn off limits in MC SUS ASC inputs,
Turn off ELP28 FH6 in MC2 Damp Filter.

After the experiment, we restored all the changed settings.

We decided the oscillation frequency, 27.25 Hz and 37 Hz, by monitoring the background PSD at MC2. But we totally took the time-dependent datas using 37 Hz because the pole frequency of some filters is around 27.25 Hz. We used python script that Alex wrote (MC_TRANS_SUM_PLOTS.ipynb, URL: /opt/rtcds/caltech/c1/Git/40m/measurements/IMC) for taking the datas. We took each data by oscillating PIT or YAW of each mirror in IMC. Measuring time was set as 10 s. The time is longer than the 100 times of 1/37 Hz. Oscillating amplitude is tabled below.

MC1P	Amplitude	MC1Y	Amplitude
Take 1	4,500	Take 1	30
Take 2	Forget taking value...	Take 2	80
Take 3	3,000	Take 3	75
MC2P		MC2Y
Take 1	75	Take 1	10,000
MC3P		Take 2	17,500
Take 1	30	MC3Y
Take 2	50	Take 1	100
		Take 2	70

In order to analyze the datas, we make python script named MC_TRANS_SUM_ANALYZE.ipynb (URL: /opt/rtcds/caltech/c1/Git/40m/measurements/IMC). We can get $a_2$ but I have some questions as listed below:

How can we treat error of $a_2$ ?
What is the unit of $A_0$ ? and How much value is it? If the unit of $A_0$ is cts, we can use each oscillating amplitude.

In this time, we use the error of $a_2$ as the quadrature component. And we use $A_0$ as the oscillating amplitude as listed above.

Result

The result is shown in the table.

MC1P	87 \pm 2 prad/cts
MC1Y	787 \pm 2 prad/cts
MC2P	533 \pm 8 prad/cts
MC2Y	2.38 \pm 0.04 prad/cts
MC3P	2.77 \pm 0.01 urad/cts
MC3Y	786 \pm 6 prad/cts

Comparing with the Anchal's result, we get much smaller error and different order... We have to reconsider the calculation method.

17484

Sun Feb 26 00:13:55 2023

Configuration

IOO MC PIT/YAW gain change

The following changes were made to the WFS MASTER IMC Pitch and Yaw gains:

Gain values for the pitch and yaw on MC1, MC2, and MC3 filters on the SUS ASC inputs have been carried over to the WFS MASTER output filters.
This was done such that Tomohiro and I could take AC measurements at an oscillation freq of 77 Hz on the pitch and yaw mirrors, while being sure that the amplitude of the AC signal being applied to each mirror is the same. The filters on the WFS output will have gains changed from 1.0 to the previously mentioned calibration values described in ELOG 17481.

The values calculated for each filter were inverses of the callibration constants. The filters at the SUS ASC inputs were modified to read gain values of 1.0 again.
See the table bellow for the values passed to each filter.
In summary:
originally IOO-MC1,2,3_PIT/YAW_GAIN = 1.0. Now:

MC1,2,3_ASCPIT/ASCYAW_GAIN >> IOO-MC1,2,3_PIT/YAW_GAIN

IOO-MC1,2,3_PIT/YAW_GAIN >> 1.0

17483

Fri Feb 24 15:21:39 2023

Large Optical Table Movement Solidworks

General

I sketched up the first encounter we will have when moving the optical table out. I'm assuming the table has already been turned onto its side. Next will be manuevering the table into the aisle along X-Arm. Solidworks' "Move Component" feature always me to move the table and see collisions. The feature stops the component from dragging and highlights the two faces which have made contact. I have not yet gotten to take the dimensions of the MC2 chamber and table, this will bethe tightest spot, so I want to get precise measurements. Though, it looks like we wont have any issues getting the table into the aisle. Atachment #1 is a top view that shows we have clearence, ~5 -7.5 in on both sides, and attachment #2 is a sectional view to show a clear pathway for pulling the table into the aisle.

Object that are Red are computer racks and Wood are walls.

Attachment 1: Capture.PNG

Attachment 2: Capture1.PNG

17482

Fri Feb 24 13:33:22 2023

Tomohiro

Updated angular actuation calibration for IMC mirrors

Alex, Anchal, and I did the following to make updated angular actuation calibration for IMC mirrors. This is the revised version of Anchal's: 40m/16125.

In order to make the calibration formulas, we consider a matrix $A$ : connecting displacements and rotations of the IMC's beam waist to PIT and YAW rotations of every mirror

$\begin{pmatrix} x_\mathrm{c} \\ y_\mathrm{c} \\ \theta_\mathrm{c} \\ \phi_\mathrm{c} \end{pmatrix} = A \begin{pmatrix} \theta_1 \\ \theta_2 \\ \theta_3 \\ \phi_1 \\ \phi_2 \\ \phi_3 \end{pmatrix}.$

The parameters used in the above equation are listed in the next table.

$x$	horizontal displacement of beam waist position
$y$	vertical displacement of beam waist position
$\theta$	PIT of the beam axis and/or each mirror
$\phi$	YAW of the beam axis and/or each mirror
$c$ (subscript)	parameters for the beam
$i = 1, 2, 3$ (subscript)	parameters for $\mathrm{MC}_i$

$\mathrm{MC}_{1, 3}$ are the flat mirrors and $\mathrm{MC}_2$ is the curved mirror in IMC. Components in $A$ are refered from F. Kawazoe+ 2011 (doi: 10.1088/2040-8978/13/5/055504). In the paper, displacement and/or rotation of the beam parameters obtained from the PIT and YAW of each mirror are obtained not by $\theta_{1, 3}, \phi_{1, 3}$ but by common or differential rotation of both two flat mirrors $\theta_\pm \equiv \theta_1 \pm \theta_3, \phi_\pm \equiv \phi_1 \pm \phi_3$ . Therefore, we divide $A$ into two parts $A_1, A_2$ (relation $A = A_1 A_2$ ):

$A_1$ : relation between the beam parameters and the PIT and YAW rotation with $\theta_\pm, \phi_\pm$

$\begin{pmatrix} x_\mathrm{c} \\ y_\mathrm{c} \\ \theta_\mathrm{c} \\ \phi_\mathrm{c} \end{pmatrix} = A_1 \begin{pmatrix} \theta_+ \\ \theta_- \\ \theta_2 \\ \phi_+ \\ \phi_- \\ \phi_2 \end{pmatrix}.$

$A_2$ : relation between $\theta_\pm, \phi_\pm$ and $\theta_{1, 3}, \phi_{1, 3}$

$\begin{pmatrix} \theta_+ \\ \theta_- \\ \theta_2 \\ \phi_+ \\ \phi_- \\ \phi_2 \end{pmatrix} = A_2 \begin{pmatrix} \theta_1 \\ \theta_2 \\ \theta_3 \\ \phi_1 \\ \phi_2 \\ \phi_3 \end{pmatrix} = \begin{pmatrix} 1 & 0 & 1 & 0 & 0 & 0 \\ 1 & 0 & -1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 1 & 0 & 1 \\ 0 & 0 & 0 & 1 & 0 & -1 \\ 0 & 0 & 0 & 0 & 1 & 0 \\ \end{pmatrix} \begin{pmatrix} \theta_1 \\ \theta_2 \\ \theta_3 \\ \phi_1 \\ \phi_2 \\ \phi_3 \end{pmatrix}.$

$A_1$ is represented by revewing F. Kawazoe+ (2011):

$A_1 = \begin{pmatrix} 0 & 0 & 0 & 0 & - \sqrt{L^2 + d^2} & 0 \\ \dfrac{R - L}{\sqrt{2}} & 0 & -R & 0 & 0 & 0 \\ 0 & \dfrac{1}{\sqrt{2}} & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & \dfrac{R - L}{R - (L + d)} & 0 & - \dfrac{R}{R - (L + d)} \end{pmatrix}.$

Here we use $R$ as RoC of $\mathrm{MC}_2$ , $L$ as height from the shorter side of the isoscele triangle, and $d$ as half-long length of the shorter side. Intuitive discussion about the components are written in the last of the log.

Transmitted power is reduced by the small displacement and/or the small rotation of the beam axis, and can be represented by the Gaussian factor. It is described in /users/OLD/kakeru/oplev_calibration/oplev.pdf by Takahashi-san:

parallel displacement

$\left( \mathrm{e}^{- \frac{\beta^2}{{2w_0}^2}} \right)^2 \approx 1 - \frac{\beta^2}{{w_0}^2}$

where $\beta$ is the small displacement of the beam waist. It corresponds to $x_\mathrm{c},~y_\mathrm{c}$ . $w_0$ is beam waist diameter inside IMC.

beam axis rotation

$\left( \mathrm{e}^{- \frac{\alpha^2}{{2\alpha_0}^2}} \right)^2 \approx 1 - \frac{\alpha^2}{{\alpha_0}^2}$

where $\alpha$ is the small rotation of the beam axis. It corresponds to $\theta_\mathrm{c}, \phi_\mathrm{c}$ . $\alpha_0$ is divergence angle of the beam and is written by $w_0$ and wavelength of laser $\lambda$

$\alpha_0 = \frac{\lambda}{\pi w_0}.$

Total power reduction is measured by multiplied gaussian factor of the displacement and the rotation. We can obtain the calibration formulas $\eta$ with summed reduction Gaussian factor

$\begin{align} &\frac{\beta (x_c (\vec{\Theta}), y_c (\vec{\Theta}))^2}{{w_0}^2} + \frac{\alpha (\theta_c (\vec{\Theta}), \phi_c (\vec{\Theta}))^2}{{\alpha_0}^2} \notag \\ &\qquad\quad= \eta_{\cdot 1\mathrm{P}}~{\theta_1}^2 + \eta_{\cdot 2\mathrm{P}}~{\theta_2}^2 + \eta_{\cdot 3\mathrm{P}}~{\theta_3}^2 + \eta_{\cdot 1\mathrm{Y}}~{\phi_1}^2 + \eta_{\cdot 2\mathrm{Y}}~{\phi_2}^2 + \eta_{\cdot 3\mathrm{Y}}~{\phi_3}^2 \notag \end{align}$

where $\vec{\Theta}$ is the vector of the PIT and YAW rotation $\vec{\Theta} \equiv \left( \theta_1, \theta_2, \theta_3, \phi_1, \phi_2, \phi_3 \right)^\mathrm{T}$ . $\eta_{\cdot i \mathrm{P}}, \eta_{\cdot i \mathrm{Y}}$ are the calibration fomulas of PIT and YAW in 40m/16125 defined by Anchal, respectively, and have a unit of $\mathrm{1/rad^2}$ . Every calibration fomula is expressed as follows:

$\eta_{\cdot 1,3 \mathrm{P}} = \frac{(R - L)^2}{2 {w_0}^2} + \frac{1}{2 {\alpha_0}^2}~,~~\eta_{\cdot 2\mathrm{P}} = \frac{R^2}{{w_0}^2},$

$\eta_{\cdot 1,3 \mathrm{Y}} = \frac{L^2 + d^2}{{w_0}^2} + \frac{(R - L)^2}{{\alpha_0}^2 \left\{ R - (L + d) \right\}^2}~,~~\eta_{\cdot 2\mathrm{Y}} = \frac{R^2}{{\alpha_0}^2 \left\{ R - (L + d) \right\}^2}.$

We intuitively describe how to obtain the components in $A_1$ . The detail is discussed in F. Kawazoe+ (2011).

$A_1 (1, 5)$ : 2-flat mirrors rotate with differential YAW $\phi_-$

When the 2-flat mirrors rotate, the shape of the isoscele triangle is thick, that is, the beam waist does not rotate but slightly displaces from its original one. Considering that the longer side of the triangle are almost perpendicular to the shorter side and $\phi_- \ll 1$ , $x_\mathrm{c}$ can be obtained by focusing on the right triangle shown in the following picture

$x_\mathrm{c} = - \sqrt{L^2 + d^2} \tan \phi_- \approx - \sqrt{L^2 + d^2} \phi_-.$

$A_1 (4, 4)$ : 2-flat mirrors rotate with common YAW $\phi_+$

From $\phi_+ \ll 1$ , new triangle beam line is very similar to the isoscele triangle by rotating $\phi_+$ from original one. So $\phi_c$ is approximated to $\phi_+$ , but actually the new one is breaked its symmetry. The result becomes as follows

$\phi_\mathrm{c} = \frac{R - L}{R - (L + d)} \phi_+.$

$A_1 (4, 6)$ : curved mirror rotates by $\phi_2$

It is similar to the case of $\phi_+$ . But the pivot to rotate the triangle is near than the case $\phi_+$ , so $\phi_\mathrm{c}$ has bigger factor than that of $\phi_-$

$\phi_\mathrm{c} = - \frac{R}{R - (L + d)} \phi_2.$

$A_1 (2, 3)$ : curved mirror rotates by $\theta_2$

It is completely the same as the discussion of linear cavity which has flat end mirror and curved input mirror.

$y_\mathrm{c} = - R \tan \theta_2 \approx - R \theta_2.$

$A_1 (2, 1)$ : 2-flat mirrors rotate with common PIT $\theta_+$

It is also the same as the linear one except that 2-flat mirrors are angled by 45 degrees. Angled 45 degrees reduce the effective rotation by factor of $1/\sqrt{2}$ . The detail is discussed in A. Freise (2010).

$y_\mathrm{c} = (R - L) \tan \left( \frac{\theta_+}{\sqrt{2}} \right) \approx (R - L) \frac{\theta_+}{\sqrt{2}}.$

$A_1 (3,2)$ : 2-flat mirrors rotate with differential PIT $\theta_-$

The differential rotation with the effect of $1/\sqrt{2}$ directly reflects to the PIT rotation of the beam

$\theta_\mathrm{c} = \frac{\theta_-}{\sqrt{2}}.$

17481

Fri Feb 24 13:29:16 2023

Updated angular actuation calibration for IMC mirrors

Also reply to: 40m/17352

Tomohiro, Anchal, and I did the following to make updates to the calibration constants for pitch and yaw on MC1, MC2 and MC3.

To acquire the data used for fitting a curve respective to the change in counts per change in mirror pitch and yaw, we utilized some code that Anchal has already developed.

The scripts used to take time averaged data points of the IMC mirrors can be found by entering the command $ s into a terminal window to enter the scripts folder. Then enter the path "SUS/angActCal"

The following scripts will be found there to be used for this experiment:

angActCal.py & parabolaFit.py

To take data we used the angActCal.py function with set values for the time averaging = 5 s, settle time = 5 s, and adjusted the offset such that we would acquire approximately 20 data points given our ASC Bias limits. We defined the limits for each plot based on where the transmission fall off from the maximum value reached an average range of 10,000 counts.

The "readChannel" for each was the "C1:IOO-MC_TRANS_SUMFILT_OUTPUT" and can be found from the site map at IOO>Lock MC> see MC2_TRANS

The adjustment channels for Pitch and yaw on each IMC mirror were entered as the offset value found in the IMC screen at ALIGNMENT OFFSETS > BIASPIT/BIASYAW > OFFSET

For the code to work, the offset switch must be turned on. parabolaFit.py

The data from MC1, MC2, and MC3 for pitch and yaw was saved to individual text files which were then entered into the parabolaFit.py function to get the results seen in attachment 1 and 2.

The above images show the printout from the plot fitting function and one of the graphs produced.

Optic ACT	Fit curve factor for DC (1/cts^2)
MC1 PIT	2.41 +/- 0.01 e-3
MC1 YAW	4.12 +/- 0.02 e-3
MC2 PIT	5.75 +/- 0.03 e-3
MC2 YAW	8.48 +/- 0.13 e-3
MC3 PIT	1.83 +/- 0.03 e-3
MC3 YAW	4.52 +/- 0.05 e-3

From the fitted curve values we then derived the equations that will soon be described further by Tomohiro (see entry _____) to arrive at the final callibration constants.

Optic ACT	Callibration constant at DC (urad/cts)
MC1 PIT	12.66 +/- 0.03
MC1 YAW	6.64 +/- 0.02
MC2 PIT	lock6.83 +/- 0.02
MC2 YAW	4.69 +/- 0.04
MC3 PIT	11.03 +/- 0.09
MC3 YAW	6.96 +/- 0.04

Final Calibration Constants for MC1, MC2, & MC3

We then utilized our calculated calibration constants (as seen bellow) to adjust the following filter parameters in the IMC control panel.

To make the updates such that the IMC screens show the correct urad values at the output of the filter banks, we must do the following steps to MC1, MC2, and MC3:

First, to make changes to our calibration filters, we must first shut off the pitch and yaw feedback loop controls.

TO do so for the Lock Filters, we will set the pitch and yaw SUS ASC inputs to 0 but entering the sitemap > IOO > C1IOO_WFS_MASTER

Nex head to action at the top right, and we can select "MC WFS relief 60s", this will relieve the values from the pitch and yaw inputs to the 40m Mode Cleaner Alignment settings to save the overall alignment and allow us to turn off the WFS servos to make the necessary adjustments on the lock filters.

Once we have waited a sufficient amount of time for the values on the ASC inputs to hover around 0, select Turn WFS ON/OFF button and choose "Turn OFF MCWFS Servo"

Next, we will press on the "on/off" button (see attachment 3 - circled in orange) for pitch and yaw found in just the LOCK FILTERS windows.

Once these are off we will stay in the same screen and adjust the gain values (boxed in yellow) for pitch and yaw.

Next, we will take the current value and divide it by the newly found corresponding calibration constant. This is to adjust for the changes we will be making on the output end of the filter banks such that all values in the feedback controls are normalized to the same scale.

The changes made here can be seen bellow:

	Damp Filter Orig	Damp Filter NEW	Lock Filter Orig	Lock Filter New
MC1 PIT	40.0	3.160	1.0	0.079
MC1 YAW	40.0	6.024	1.0	0.151
MC2 PIT	5.0	0.732	1.0	0.146
MC2 YAW	5.0	1.066	1.0	0.213
MC3 PIT	3.0	0.272	1.0	0.091
MC3 YAW	5.0	0.718	1.0	0.144

Now that these changes have been made in the damp and lock filter banks, with the pitch and yaw feedback loops STILL OFF, we may adjust the newly made calibration filters for pitch and yaw (as seen in attachment 4).

The "P" and "Y" filters may be opened (boxed in red) and we may adjust the gain (circled in yellow). Because each of these filters have just been created, the value is set to 1. This value can be completely replaced with the calibration constant found in our table above. Thus we will now change MC1 Pitch to have a "gain" of 12.66 and so forth.

Once each of the calibration filters have been updated, you may go back into the damp filters and reinitiate the feedback loops.

Once all values have been entered,

This concludes the updating of the IMC filter calibration constants at DC.

Attachment 1: angActCal_C1-SUS-MC1_BIASPIT_OFFSET_to_C1-IOO-MC_TRANS_SUMFILT_OUT_1361152703.png

Attachment 2: Screenshot_2023-02-23_16-47-58.png

Attachment 3: InkedScreenshot_2023-02-23_17-02-13.jpg

Attachment 4: InkedScreenshot_2023-02-23_17-02-49.jpg

17478

Thu Feb 23 14:55:49 2023

BH55 and BH44 orthogonality checks

Ideally, BH55 and BH44 should give orthogonal signals to lock LO phase (40m/17302).
This was checked with various interferometer configurations.
BH55 and BH44 are indeed orthogonal in ITM single bounce and MICH, but was not measurable in FPMI.
Maybe we should investigate BH44 in MICH BHD configuration first to see why BH44 is very noisy in FPMI.

Method:
- X-Y plotted BH55_Q and BH44_Q and fitted with an ellipse to derive amplitude of each signal and phase difference between them.
- Amplitude and phase differences are calculated using the following equations, where (ap, bp) are the semi-major and semi-minor axes, respectively, and phi is the rotation of the semi-major axis from the x-axis. (Thanks to Tomohiro for checking the calculations!)

xAmp = np.sqrt((ap * np.cos(phi))**2 + (bp * np.sin(phi))**2)
yAmp = np.sqrt((ap * np.sin(phi))**2 + (bp * np.cos(phi))**2)
phaseDiff = np.arctan(bp/ap*np.tan(phi)) + np.arctan(bp/ap/np.tan(phi))

Jupyter notebook: /opt/rtcds/caltech/c1/Git/40m/scripts/CAL/BHD/MeasurePhaseDiff.ipynb

- This was done un following 4 configurations.
- ITMX single bounce vs LO
- ITMY single bounce vs LO
- AS beam in MICH locked with AS55_Q vs LO
- AS beam in FPMI locked with REFL55/AS455 vs LO
- For each configuration, RF demodulation phases were tuned to minimize I.
- Statistical error was estimated by calculating the standard deviation of 3 measurements.

- Also, FPMI BHD sensing matrix was measured when FPMI is locked with REFL55/AS55, and LO_PHASE is locked with BH55_Q or BH44_Q.

Jupyter notebook: /opt/rtcds/caltech/c1/Git/40m/scripts/CAL/SensingMatrix/ReadSensMat.ipynb

Result of BH55/BH44 orthogonality check:
- ITMX single bounce vs LO
Demod phase Amplitude Phase Diff BH55_Q -94.4 +/- 0.2 deg 600.4 +/- 0.6    BH44_Q -9.0 +/- 0.2 deg 124.3 +/- 0.2 -86.7 +/- 0.1 deg
- ITMY single bounce vs LO
Demod phase Amplitude Phase Diff BH55_Q -92.9 +/- 0.3 deg 588.0 +/- 0.3    BH44_Q -8.9 +/- 0.3 deg 123.0 +/- 0.1 -87.2 +/- 0.1 deg
- AS beam in MICH locked with AS55_Q vs LO
Demod phase Amplitude Phase Diff BH55_Q -68.7 +/- 0.8 deg 44 +/- 1    BH44_Q -28.5 +/- 1.7 deg 10.3 +/- 0.1 -84 +/- 2 deg
- AS beam in FPMI locked with REFL55/AS455 vs LO
Demod phase Amplitude Phase Diff BH55_Q 35 +/- 3 deg 257 +/- 4    BH44_Q -16 +/- 3 deg 44 +/- 1 -77 +/- 3 deg
- Attachmented pdf contain example X-Y plots from each configuration. For ITM single bounce and MICH, BH55 and BH44 seems to be orthogonal, but for FPMI, ellipse fit does not go well.
- Difference in the BH55 demodulation phase for ITMX single bounce and ITMY single bounce (1.5 +/- 0.4 deg) agrees with past measurement and agree marginally with Schnupp asymmetry (40m/17274).
- Maybe we can derive some length differences using these demodulation phases.

Result of FPMI sensing matrix measurements:
- Below is the sensing matrix when FPMI is locked with REFL55/AS55, and LO_PHASE is locked with BH55_Q. BH44 is noisier than BH55, and the response to LO1 is consistent with zero. This is also consistent with BH44 being orthogonal to BH55, but the error bar is too large to say.

Sensing matrix with the following demodulation phases (counts/m) {'AS55': -168.5, 'REFL55': 92.32, 'BH55': -110.0, 'BH44': -8.93097234187195} Sensors DARM @307.88 Hz CARM @309.21 Hz MICH @311.1 Hz LO1 @315.17 Hz AS55_I (-2.49+/-8.35)e+10 [90] (+2.36+/-0.85)e+11 [0] (-0.64+/-3.99)e+10 [0] (+0.57+/-4.07)e+09 [0] AS55_Q (-3.50+/-0.08)e+11 [90] (+0.09+/-1.20)e+11 [0] (-0.79+/-8.66)e+09 [0] (-0.70+/-5.96)e+08 [0] REFL55_I (+0.72+/-8.09)e+11 [90] (-1.42+/-2.75)e+12 [0] (+0.00+/-1.37)e+11 [0] (-0.38+/-2.78)e+09 [0] REFL55_Q (+0.19+/-1.93)e+11 [90] (-2.14+/-6.92)e+11 [0] (+0.00+/-3.16)e+10 [0] (+0.17+/-1.19)e+09 [0] BH55_I (-1.41+/-0.55)e+11 [90] (+1.46+/-2.28)e+11 [0] (-1.60+/-3.72)e+10 [0] (-0.07+/-3.05)e+09 [0] BH55_Q (+2.05+/-3.10)e+10 [90] (-1.72+/-4.86)e+10 [0] (-0.31+/-2.19)e+10 [0] (-3.06+/-0.87)e+09 [0] BH44_I (-0.41+/-2.03)e+11 [90] (+0.10+/-2.39)e+11 [0] (+0.06+/-1.31)e+11 [0] (-0.01+/-2.71)e+10 [0] BH44_Q (+0.14+/-3.23)e+12 [90] (+0.02+/-3.67)e+12 [0] (+0.07+/-2.03)e+12 [0] (-0.02+/-4.22)e+11 [0] BHDC_DIFF (+8.49+/-0.47)e+11 [90] (-0.06+/-2.93)e+11 [0] (-0.16+/-1.01)e+10 [0] (-0.27+/-2.04)e+09 [0] BHDC_SUM (-2.30+/-0.11)e+11 [90] (+0.68+/-7.92)e+10 [0] (-0.44+/-3.33)e+09 [0] (-0.63+/-5.63)e+08 [0]

- Below is the sensing matrix when FPMI is locked with REFL55/AS55, and LO_PHASE is locked with BH44_Q. BH44 response to LO1 is again consistent with zero. Locking LO_PHASE with BH44 is not robust. Also, BHDC_DIFF response to DARM is less, compared with LO_PHASE locked with BH55_Q. This means that BH55 is somehow better than BH44 in our FPMI BHD, which contradicts with simulations (with no contrast defect and DARM offset).

Sensing matrix with the following demodulation phases (counts/m) {'AS55': -168.5, 'REFL55': 92.32, 'BH55': -110.0, 'BH44': -8.93097234187195} Sensors DARM @307.88 Hz CARM @309.21 Hz MICH @311.1 Hz LO1 @315.17 Hz AS55_I (-7.56+/-4.89)e+10 [90] (+1.61+/-1.05)e+11 [0] (+0.51+/-2.48)e+10 [0] (+0.88+/-8.02)e+08 [0] AS55_Q (-3.62+/-0.05)e+11 [90] (+0.02+/-1.23)e+11 [0] (+0.67+/-3.73)e+09 [0] (+0.02+/-1.28)e+08 [0] REFL55_I (+1.09+/-8.12)e+11 [90] (-1.47+/-2.82)e+12 [0] (+0.01+/-1.34)e+11 [0] (+2.20+/-5.29)e+08 [0] REFL55_Q (+0.22+/-1.93)e+11 [90] (-1.83+/-7.23)e+11 [0] (+0.02+/-3.18)e+10 [0] (+0.56+/-1.17)e+08 [0] BH55_I (-1.21+/-0.08)e+12 [90] (+0.17+/-4.31)e+11 [0] (-1.24+/-3.02)e+10 [0] (-0.30+/-3.55)e+09 [0] BH55_Q (-3.83+/-0.30)e+11 [90] (-0.12+/-1.42)e+11 [0] (-0.61+/-1.96)e+10 [0] (-0.21+/-1.49)e+09 [0] BH44_I (-0.22+/-2.01)e+11 [90] (-0.07+/-2.30)e+11 [0] (-0.02+/-1.27)e+11 [0] (+0.08+/-2.62)e+10 [0] BH44_Q (-0.77+/-8.27)e+11 [90] (-0.13+/-9.51)e+11 [0] (-0.04+/-5.23)e+11 [0] (+0.02+/-1.08)e+11 [0] BHDC_DIFF (+1.94+/-0.81)e+11 [90] (-0.58+/-1.84)e+11 [0] (+0.18+/-3.53)e+10 [0] (-0.49+/-3.84)e+09 [0] BHDC_SUM (-2.22+/-0.12)e+11 [90] (+0.66+/-7.70)e+10 [0] (-1.04+/-3.97)e+09 [0] (+0.31+/-6.10)e+08 [0]

Other notes:
- TRX and TRY are noisier at ~28 Hz when locked with REFL55/AS55 than when locked with POX/POY. DARM signal seems to be contaminated with broad 28 Hz noise. Needs investigation of the cause.
- BS oplev loops seem to be close to unstable. When FPMI is unlocked, BS is kicked significantly.

Next:
- Repeat measurement in 40m/17351 with BH44.
- Compare LO phase noise in MICH configuration when LO_PHASE is locked with BH44 and BH55.
- Investigate 28 Hz noise in FPMI
- Tune BS local damping loops

Attachment 1: LSC-BH44_Q_ERR_DQ_20230223.pdf

17477

Wed Feb 22 23:40:48 2023

Adding calibration constants for sus matrix and filter control buttons to the sus control screen

Calibration

The callibration constants were updated for the oplev pitch and yaw. The values were changed as denoted in 17471 were:

PITH: 175.7→ 155 cts/urad

YAW: 193 → 241 cts/urad

To make these changes for the oplev callibration constants I went to ETMY - SELECTED OPLEV SERVO BOX

I then opened OLMATRIX and turned off PITCH and YAW servos in the ETMY SUSPENSION SCREEN such that the system does not attempt to actively make corrections while values are being changed.

Then I adjusted the matrix to include our updated calibration constants and reinitiated the oplev ptich and yaw servo's

This updated the calibration constants for everything

The next change that was made was the addition of the calibration filters for position, pitch, yaw and side into the sitemap view for the suspension systems.

Adding calibration filters will allow us to callibrate the pos, pitch, yaw, and side to true values of urad and umeters (see 17459)

The final screen may be seen bellow (the updated area is outlined in red):

When each of the filter buttons is clicked, the following screen will now appear (circled in yellow is the calibration constant gain we will be calculating and entering into the system):

To create the edits to the controls screen we must complete the following process

We can edit the original screen - right click > evaluate > edit this screen

Then I adjusted the width of the overall screen, and moved the right half of the modules over to the right so I could fit in some filter buttons. I then Navigated to the c1ioo wfs master screen using the open feature to copy a pre existing filter module

I then adjusted the filter module and its contents to correspond to the features and autogenerated model files from RTCDS

There was some rearranging and adjusting needed to get these files in place first. The autogenerated files from the RTCDS can be found in dir = "/opt/rtcds/caltech/c1/medm/c1sus/"

They were autogenerated with names "C1SUS_BS_PITCAL.adl", "C1SUS_BS_POSCAL.adl", "C1SUS_BS_YAWCAL.adl","C1SUS_BS_SIDECAL.adl"

We copied these files to dir = "/opt/rtcds/userapps/trunk/sus/c1/medm/templates/NEW_SUS_SCREENS/"

The file names were changed to "SUS_PITCAL.adl", "SUS_POSCAL.adl", "SUS_YAWCAL.adl", "SUS_SIDECAL.adl"

The directory we placed them in is where the models for c1 sus can be found that are referenced by the sitemap suspension monitor screen

Each file was then opened in Vscode and a few changes were made such that the specific naming values referenced by the different screens of the sitemap and different optics, are replaced by the overarching values seen in each instance of the screens.

There are approximately 50 referenced file names of "C1:SUS-BS_PITCAL" etc. In each instance we made the following changes:

"-BS" was changed to "-$(OPTIC)"

"C1:" was changed to "$(IFO):"

The new strings should read "$(IFO):SUS-$(OPTIC)_PITCAL"

Once this change was made we can now right click on the filter module box, click on "Label/Name/Args" button

In the display file, we must add the path name for the calibration directory "/opt/rtcds/userapps/trunk/sus/c1/medm/templates/NEW_SUS_SCREENS/SUS_POSCAL.adl"

And for the arguments box we will enter OPTIC=$(OPTIC), IFO=$(IFO)

You can also copy and paste the directory names in the file boxes using right click copy from the file manager and paste into the box using a single click of the mouse scroller wheel

Lastly, the PV limits were changed for each number output right click value box > PV limits > Precision > Source changed to "Default" with a value of 1.

The shown value of the position, pitch, yaw, and side was then changed to show the output from the newly added filter. This is done also by right clicking the value box and adjusting the "Readback Channel".

Value changed from "$(IFO):SUS-$(OPTIC)_TO_COIL_1_#_INMON" to the outputs from the filters which are

"$(IFO):SUS-$(OPTIC)_POSCAL_OUTMON" (for others changing POSCAL to the appropriate variable)

This is how to edit and add the Medm screens for single suspension optics into the sitemap IFO SUS screen

Lastly, Tomohiro and I worked on acquiring 6 data sets from DC stepping through adjustments in pitch and yaw for MC1, MC2 and MC3. These datasets will be fit quadratically and combined with more tests dine by AC driving the stepper motors tomorrow to find the calibration constants for the mirrors.

Attachment 2: InkedScreenshot_2023-02-22_18-28-41.jpg

Attachment 3: InkedScreenshot_2023-02-22_18-29-00.jpg

17476

Wed Feb 22 17:32:16 2023

BH55 and BH44 both amplified

Since we need more signal for both BH55 and BH44 to compare LO phase locking scheme, BH55 and BH44 RF outputs are now amplified with ZFL-1000LN+ and ZFL-500HLN+ respectively (see Attachment #1).
The amplifiers each draw ~0.1 A current of 15V DC power supply, and Sorensen power supply now reads 6.9 A (see Attachment #2).
With ITMX single bounce and LO beam fringing, BH55_Q (45 dB whitening gain, C1:LSC-BH55_PHASE_R=-110 deg) gives ~500 counts in amplitude, and BH44_Q (24 dB whitening gain, C1:LSC-BH44_PHASE_R=4.387 deg) gives ~100 counts in amplitude (and they are orthogonal) (see Attachment #3).

Attachment 1: BH55BH44.JPG

Attachment 2: Sorensen.JPG

Attachment 3: Screenshot_2023-02-22_17-35-27_BH55BH44.png

17475

Tue Feb 21 19:04:15 2023

XARM green laser lock debugging

ALS

I retook the last spectrum measurement of ALS beatnote fluctuations, with the HEPA on and off. The top plot corresponds to BEATY, and the bottom plot corresponds to BEATX. The 560 Hz peak doesn't seem to be dependent on the status of the HEPA. The noise floor change in BEATY is probably due to drift of the beatnote frequency.

Attachment 1: beatx_beaty_spectrum_hepa_on_off.pdf

17474

Mon Feb 20 16:35:15 2023

I added a less agressive low pass filter to give some more phase margin, and then increased the overall gain by 4x. There is now some suppression around 1 Hz.

In the attached plot:

HEPA ON is the grey traces. Nothing surprising there.
The dark PURPLE traces are HEPA OFF, old gain/filter settings.
Colorful traces: RLP20 instead of RLP12. input gain slider = 4.0

Its clear from this that the WFS2 PIT servo has a very low gain. There's no UGF bump in the spectra.

I also added a 6 Hz : 3 Hz pole:zero pair to give some phase lead. Turning this on reduces some gain bump in pitch, but makes the WFS1 Yaw loop oscillate.

Attachment 1: wfs1-gain-tuning.png

Attachment 2: mcwfs-servo.png

17473

Mon Feb 20 15:27:32 2023

rana

Computers

pianosa software issues

notes 20-Feb-2023

* emacs doesn't run in base conda path (cds). LD_LIBRARY_PATH errors

* works fine if I do 'conda deactivate'. Something weird with our conda env?

* did apt install emacs, xemacs, terminator,

* these should be in the default workstation install

* arrgg! (cds) ~>dataviewer bash: dataviewer: command not found

* looks like apt installs, made dataviewer executable disappear?

17472

Mon Feb 20 14:20:04 2023

Made a comparison plot between the WFS1 PIT loop and the model. There is good agreement.

I have had trouble increasing the UGF to > 1 Hz. Usually some instability ~1 Hz.
Took a swept sine TF of WFS1 P, with the all 6 angular loops closed. The UGFs are all <0.1 Hz or so, so I think it doesn''t affect the loop shapes around 1 Hz.
The model was not agreeing with the measurement. In addition to the pendulum TF and the WFS1 PIT filters, I had to add the Bounce/Roll mode bandstop filters, and the 28 Hz elliptic low pass which is the post DAC low pass (aka dewhitening filters).
I expect that some of the wiggles around 1 Hz are due to modeling the pendulum as a viscous damped pendulum, rather than the OSEM damping loop.

Next, I will try to do some loopology to increase the phase margin around 1-3 Hz. HEPA in OFF state for now - please turn on in the morning.

Attachment 1: wfs1pit.pdf

17471

Thu Feb 16 23:54:11 2023

Yaw and Pitch Calibration constants for ETMY op-lev

Daily Progress

This work was done by Ancal and I.

To recallibrate the op-lev for ETMY, a python script was first written to calculate the change in distance in x or y that the photodiode array will see when the mirror incurs a change in yaw or pitch. The python script approximates d by integrating, using a reimann sum, the area under a gaussian curve, given by I(r)= I_oexp(−2r²/ 2w(z)²), where r is the radial position, and w(z) is the waist (radius) size of the gaussian beam where power reaches 1/e²of its maximum. The distance d, is the difference from the center of the gaussian to the point at which the beam profile has a normalized area under the curve equal to that of the percent of the beam profile showing on one half of the circular photodiode array.

Above, the gaussian is related to the translation of the beam profile on the photodiode where the area calculated under the curve of the gaussian, is equivalent to the ratio of the beam profile in 2 adjacent quaters of the photodiode array.

The gaussian, is directly related to the waist size of the laser beam profile, and thus a beam profiler was used to calculate the waist size over an average of 100 takes. Due to the thickness of the beam profiler, we were unable to get a direct measurement of the size of the beam at the exact location of the photodiode. Instead, we took two seperate measurements while moving the profiler 1 inch further away from the photodiode and back calculated the average size of the beam at the photodiode assuming that at this distance away from the source, the beams width would expand linearly. This provided a 2*waist size of 1625 ± 40 um.

image above displays the laser beam profiler used to approximate the waist size of the op-lev laser.

The physically calculated translation of the beam profile, d, can then be used to determine the overall angle, theta, that the mirror has moved to create this offset. The relation between distance and theta is Theta = d/2R, where R is the length from the mirror surface to the photodiode. R was then measured by hand over the optics table, and estimated to the best of our ability using the accurate autocad drawings of ETMY. This provided us with an R length of 1.76 ± 0.02 meters.

Image above shows the current system in place for converting the photodiode counts into microradians. The calibration constant is implemented at the last green filter boxes for pitch and yaw.

Lastly, to calculate the callibration constants, a series of tests were run on the ETMY suspeneded mirror. First, a time averaged value of the photodiode counts was taken with the mirror locked in place. Next, pitch and yaw were adjusted by 10 counts seperately, and the photodiode outputs recorded. This was done again but by moving the mirror 50 counts in pitch and yaw (seperately). The final result of the difference of the calculated theta values over the difference of pitch or yaw counts provided the following callibration constants:

Pitch moved +10 counts: 131 ± 5 cts/urad

Pitch moved +50 counts: 155 ± 5 cts/urad

Yaw moved +10 counts: 237 ± 5 cts/urad

Yaw moved +50 counts: 241 ± 5 cts/urad

Given our results, we believe that the values found for our 50 count translation to be the best approximation of the calibration constant due to its movement being more significant than that of the change seen from adjusting yaw or pitch by only 10 counts.

Next steps will be to update the values in the controls system and improve the python script to be more autonomous rather than a a step by step calculation.

17470

Thu Feb 16 18:40:13 2023

XARM green laser lock debugging

ALS

[Rana, Radhika]

Yesterday we looked at the out-of-loop PDH error signal of the AUX laser and determined that the LO phase needed significant adjustment. Previously I suspected that the LO phase knob was not actually connected to the circuitry, and we confirmed this looking inside the PDH servo box. Instead we shifted the modulation frequency towards a large PZT resonance in order to obtain a phase shift. (Original frequency: 231.25 kHz.) On a scope it looked like the PDH error signal was improving.

Today I manually swept across modulation frequency in increments of 5 kHz. Qualitatively the PDH signal looked the cleanest between 285 and 290 kHz [Attachment 1]. Here the linear region spans 2V, although it could still be larger in amplitude relative to the side peaks. More fine tuning is still remaining, and at this frequency I'll measure spectra + time series of the err and control signals.

Attachment 1: IMG_4494.JPG

17469

Thu Feb 16 15:25:52 2023

XARM green laser lock debugging

ALS

After seeing a 560 Hz peak in the XAUX REFL PD signal, I took spectra of the PDH error signal (post-demod) [Attachment 1]. The peak remained, warranting further investigation.

I disconnected the XAUX PDH loop (including PZT modulation) and looked at the beatnote between the PSL (locked to IMC) and the free-running XAUX laser. Attachment 2 shows the PSL-XAUX beatnote alongside the PSL-YAUX beatnote (both around 60 MHz). Note that the YAUX PDH loop was already disconnected, but I added a terminator to the PZT input BNC. Here the 560 Hz peak originating from the XAUX laser is clear. (It is also interesting that the BEATY signal has a significant comb structure compared to BEATX.)

Anchal suggested I tune the XAUX temperature for the frequency difference to switch signs (keeping magnitude at 60 MHz). The result is in Attachment 3 - the 560 Hz peak remained, showing it's not a local temperature-dependent feature.

From this is seems the 560 Hz noise is coming from the XAUX laser.

Attachment 1: xaux_pdh_err_spectrum.pdf

Attachment 2: beatx_beaty_spectrum1.pdf

Attachment 3: beatx_beaty_spectrum2.pdf

17468

Thu Feb 16 14:44:06 2023

FPMI BHD with BH55 recovered

FPMI BHD with LO phase locked using BH55 is recovered after 60 Hz frequency noise saga.
Attachment #1 shows the calibrated FPMI spectrum with RF(AS55_Q) readout and BHD, compared with those taken on January 13 (40m/17400, before BH44 installation).
There is unknown excess noise at round 30-40 Hz. This is not from MC2 DAC noise, as turning on/off dewhitening filters didn't make a difference.
Attachment #2 shows the samething but zoomed at 60 Hz. 60 Hz noise is actually reduced by an order of magnitude compared with what we had before BH44 installation.
Note that RF amp for BH55 which was there on January 13 was removed now (40m/17413).
LO_PHASE is locked with BH55_Q, under whitening gain of 45 dB, whitening filter on, C1:LSC-BH55_PHASE_R=-110 deg, C1:HPC-LO_PHASE_GAIN=-10, FM5 and FM8. This gives UGF of ~20 Hz (we used to be able to get ~100 Hz, but not possible now).

Locking LO_PHASE with BH44 is not stable now, probably due to small optical gain. We might have to install RF amp for BH44.

Next:
- Check the beam alignment to BH44 RF PD
- Install RF amp for BH44
- Re-install RF amp for BH55

Attachment 1: FPMI_calibrated_noise_20230216.pdf

Attachment 2: FPMI_calibrated_noise_20230216_60Hz.pdf

17467

Wed Feb 15 20:08:18 2023

looking at some IMC WFS swept sines, it seems like there is poor margin around 1 Hz
increasing the overall gain (input) by 2x makes the whole system shake a lot at ~1Hz
increasing the input gain from 1 to 4 makes the lock break due to oscillations
I have turned the input slider to 0.5 just now, but it will revert to 1 after the next lock loss for tonights testing
we can use the observations from now for an hour or so to see if 0.5 is better for the 1 Hz behavior (lets look at the summary pages)

17466

Wed Feb 15 16:16:59 2023

IMC optics Coil Output Filter corrections

Overtime the coil output filters on IMC optics have drifted into a bad configuration. Today at the meeting, Rana told us the correct configuration for these filters. I'll summarize this here and we have changes the filters on all IMC optics, MC1, MC2, and MC3 to match this configurations:

MC1 and MC3

Analog side:

Both MC1 and MC3 have a 28 Hz 5th order elliptical low pass filter as teh dewhitening filter in LIGO-D000316

Digital side:

At the coil output filters named as C1:SUS-MC1_ULCOIL, the filter module FM9 is connectd in RTCDS to the analog dewhitening filter such that only one of the two can remain ON. So For MC1 and MC3, we put a ellip("LowPass", 5, 1, 50, 28) filter on FM9 for all 5 coil output filters.

Note: We do not add a inverse dewhitening filter at FM10 like most other optics as inverting this filter will create resonant peaks at the dips of the elliptical filter which we want to avoid and we anyways do not use MC1 and MC3 optics for any kind of actuation above 20 Hz.

MC2

Analog side:

For MC2, the dewhitening filter is a 10 Hz pole, 30Hz zero like most other suspended optic.

Digital side:

At the coil output filters named as C1:SUS-MC2_ULCOIL, the filter module FM9 is connectd in RTCDS to the analog dewhitening filter such that only one of the two can remain ON. So For MC2 we put a SimDW filter which is matched to the anlog filter. We also put a InvDW filter on FM10, which is the analytical inverse of the SimDW filter. This filter does the anti-dewhitening required on the digital side and should be always ON.

To MC2 equivalent to other IMC optics in terms of overall transfer function for the local damping loops and ASC loops, we need additional 28 Hz elliptical low pass filter in these loops. But such a filter should not be in the path of LSC feedback when MC2 is used for locking CARM with a bandwidth of ~100 Hz. Thus, we put a ellip("LowPass", 5, 1, 50, 28) filter on FM6 of the following filters, which should be always ON as well:

C1:SUS-MC2_ASCPIT
C1:SUS-MC2_ASCYAW
C1:SUS-MC2_SUSPOS
C1:SUS-MC2_SUSPIT
C1:SUS-MC2_SUSYAW
C1:SUS-MC2_SUSSIDE

Effect on 60 Hz Noise

With the above changes, we see that the 60 Hz noise is same as the previous levels when we use the analog dewhitening filter (28 Hz elliptical filter) for MC1. We can move forward with our science experiments with that configuration but there is still something fishy about MC1 in comparison to MC3 which does not have this behavior. So this still needs to be looked at in future.

Wiki page for filter details and configurations

Information of this kind should be stored in a wiki page in my opinion. We should have a page where we list all common filter configurations for our suspensions and other loops, that can be generally classified and is useful for understanding legacy configuration for future folks who work here. I'm starting such a wiki page here, where I'll dump more information as I collect it and get time. Everyone is encouraged to update this in there free/procrastination times.

17465

Wed Feb 15 12:07:35 2023

ASC model updated to take inputs from IMC WFS

I have updates the ASC model inside c1ioo.mdl file to take inputs from IMC WFS when selected with AS option (on the left side of AS WFS block. I've also implemented the missing lockin option in this model. Currently the old AWS model is still in c1ioo which will be removed once we have successfully used the new ASC model for locking AS WFS loops for YARM. Now ETMX and ETMY QPD signals are also available in the input matrix for use and available outputs are ETMs, ITMs, BS, PRM, and SRM.

While changing these models, I also removed use of RFM model in ASC as this is not required anymore. The IPC from any model to any model can be done directly now. Overtime, c1rfm would be retired by removing one channel connection at a time.

Attachment 1: Screenshot_2023-02-15_12-09-10.png

17464

Tue Feb 14 18:39:53 2023

Bandstop widened for ITMX BounceRoll filter module

SUS

[Rana, Radhika]

While discussing xarm AUX laser locking, we noticed excess motion of ITMX. We took spectra of all ITMX sensor outputs and observed a 16 Hz peak, corresponding to the bounce mode of the optic [Attachment 1, 2 (zoomed)]. The UL sensor in particular is sensitive to the bounce DOF. A peak at the roll resonance can also be seen.

To suppress the bounce resonance, we altered the BounceRoll filter in the SUSPOS, SUSPIT, and SUSYAW filter modules. The bounce bandstop filter was widened to the range 15.25-17 Hz [Attachment 2]. The roll bandstop filter was left as is.

Attachment 1: ITMX_sus_sensors.pdf

Attachment 2: ITMX_sus_sensors_zoomed.pdf

Attachment 3: ITMX_sus_bounceroll.pdf

17463

Tue Feb 14 10:49:04 2023

MC1 electronics diagram and cable diconnection tests

Below are summary of electronics around MC1 and cable disconnection tests.
These suggest that the 60 Hz noise is probably from somewhere between DAC and the coil driver.
For now, we can work on IFO with SimDW off.

MC1 local damping electronics diagram:
Vacuum Flange
|| DB25 cable x2
Satellite Amp Chassis (LIGO-S2100029, LIGO-D1002818)
|| DB9 split cable
Suspension PD Whitening and Interface Board (LIGO-D000210)
||| 4pin LEMO x3
Anti-aliasing filter
|
ADC
|
CDS
(SimDW is zpk([35.3553+i*35.3553;35.3553-i*35.3553;250],[4.94975+i*4.94975;4.94975-i*4.94975;2500],1,"n") gain(1.020); InvDW is the inverse)
|
DAC
|
SOS Dewhitening and Anti-Image Filter (LIGO-D000316) Shared with MC3
(has 2ea. 800 Hz LPF & 5th order, 1 dB ripple, 50 dB atten, 28Hz elliptic LPF that can be turned on or bypassed)
||||| SMA-LEMO cable x5
("test in" are used; inputs can be disconnected with watchdogs)
SOS Coil Driver Module (LIGO-D010001, LIGO-D1700218)
(HV offsets from Acromag are added at the output (independent from watchdogs))
|| DB9 split cable
Satellite Amp Chassis

Disconnecting cables:
- Disconnecting cables between Satellite Amp Chassis and Suspension PD Whitening and Interface Board didn't help reducing 60 Hz noise.
- Disconnecting LEMO cables between Suspension PD Whitening and Interface Board and Anti-aliasing filter didn't help reducing 60 Hz noise.
- Turning off C1:SUS-MC1_SUSPOS/PIT/YAW/SIDE outputs didn't help reducing 60 Hz noise.
- Turning off SimDW reduced 60 Hz noise.
- Turning off watchdogs reduced 60 Hz noise.

Dewhitening filters:
- When 60 Hz frequency noise was high, SimDW was on, but InvDW was off, which is in a weired state.
- Now, all the MC suspensions have SimDW turned off and InvDW turned on (which supposed to turn on analog dewhitening filter, which is probably 28 Hz ELP which has a notch at 60 Hz)
- Probably, when realtime model modifications for BH44 was made on Jan 17, coil dewhitening filter situation was not burt restored correctly, and we started to notice 60 Hz noise (which was already there but didn't notice because of dewhitening).
- See 40m/17431 for the timeline, possibly related elogs 40m/17359, 40m/17361 about MC1 dewhitening switching on Dec 14-16.

Next:
- Check if analong dewhitening filter actually has 28 Hz ELP by measuring transfer functions
- Design SimDW and InvDW to correctly take into account of real dewhitening filters

17462

Mon Feb 13 17:35:20 2023

60 Hz frequency noise is coming from MC1 coils

[Anchal, Yuta]

We think we have narrowed down the source of 60 Hz noise to one fo the following possibilities:

Ground loop present along the MC1 suspension damping loop
60 Hz DAC noise on inputs of MC1 coil driver
60 Hz noise injected at dewhitening board before the dewhitening filter

The second and third cases are unlikely because we see 60 Hz noise present only in MC1 coils, not MC3 coils while they both share the same connection from DAC to SOS dewhitening filter boards as they share the SOS dewhitening board D000316-A. So it is unlikely that only the MC1 channels have this noise while the MC3 channels do not.

This inference was made from following observations:

Change	Reduction in noise at C1:LSC-YARM_IN1_DQ (dB)
Turn off damping loops, keep coil output enabled	0
Turn off coil outputs (only fast actuation)	43
Turn ON Analog Coil Dewhitening Filter on one face coil only	30
Turn ON Analog Coil Dewhitening Filter on all face coils (attachment 1)	43

Note: Turning ON analog dewhitenign on MC1 coil is done by turning off FM9 switch which is the simulated digital dewhitening filter. Also note that theanalog dewhitening filter has an attenuation of 30 dB at 60 Hz.

MC1 has an unconvetional setup where the satellite amplifier is from the new generation while the coil driver and dewhitening boards are from the old generation. The new generation satellite amplifiers sen PD signal through differential ended signals but the old generation PD whitening interface expects single ended inputs, so we ahve been using PD monitor outputs from the satellite amplifier which connects the ground of the two boards to each other. Maybe this is the reason for the ground loop.

Attachment 1: YARM_calibrated_noise_20230213_Hz_MC1SimDWOnOff.pdf

17461

Mon Feb 13 11:54:54 2023

60 Hz frequency noise is coming from MC1 coils

[JC, Yuta]

We have found that MC1 coils are causing 60 Hz noise.
Tripping watchdogs for MC1 coils reduced 60 Hz noise seen in YARM by a factor of 100.

Method:
- Locked YARM with POY11 and measured YARM sensitivity to use it for 60 Hz frequency noise monitor0.187493**0.5
- Tripped MC1, MC2, MC3 coil output watchdogs to see if they are causing this 60 Hz frequency noise. IMC WFS were turned off.

Result:
- Attachment #1 is YARM sensitivity and MC_F in Hz with MC1,2,3 untripped (dotted) and MC1 tripped (solid).

YARM (PSL locked vs Yarm), MC1,2,3 untripped: 6.0e2 Hz/rtHz (2.6e2 Hz RMS)
MC_F (sum of noises in IMC loop), MC1,2,3 untripped: 4.8e4 Hz/rtHz (2.1e4 Hz RMS)
YARM (PSL locked vs Yarm), MC1 tripped: 6.6e0 Hz/rtHz (2.9e0 Hz RMS) -- reduced by a factor of 100
MC_F (sum of noises in IMC loop), MC1 tripped: 4.7e4 Hz/rtHz (2.0e4 Hz RMS)

- We have also tried tripping MC2 and MC3 coils, but they didn't make much difference.
- Untripping only one of MC1 face coils created 60 Hz frequency noise, so all the face coils seem to have the same level of 60 Hz noise.

Next:
- Inspect around MC1 coil driver

Attachment 1: YARM_calibrated_noise_20230213_Hz.pdf

Attachment 2: Screenshot_2023-02-13_12-23-23_TrippingMC1.png

17460

Thu Feb 9 17:33:34 2023

60 Hz noise investigations around IMC, part 6, TTFSS

[Anchal, Yuta]

Measurements yesterday (40m/17458) suggested that 60 Hz noise is injected after MC_F is picked-off.
So, we terminated PSL PZT input at several points to see where 60 Hz noise is injected.
It seems like the 60 Hz frequncy noise we see in MC_F is from TTFSS box, but the 60 Hz noise we see in YARM is not limited by this.

The 60 Hz noise we see in YARM is probably limited by IMC length noise.

Method:
- We terminated PZT input to the PSL laser at various points one by one and monitored 60 Hz frequency noise using BEATX. PSL shutter was closed and IMC was not locked.

Result:
- Below is the result at 60 Hz (RMS is calculated using a bandwidth of 0.187493 Hz)

Reference from 40m/17458, YARM (PSL locked vs Yarm): 6.5e2 Hz/rtHz (2.8e2 Hz RMS)
Reference from 40m/17458, MC_F (sum of noises in IMC loop): 4.9e4 Hz/rtHz (2.2e4 Hz RMS)
MC_F when PSL shutter is closed but MC servo board configuration at IMC locked state: 2.7e2 Hz/rtHz (1.2e2 Hz RMS) -- this gives IMC loop gain enhanced sensing noise

BEATX free (PSL free vs Xend free): 3.5e3 Hz/rtHz (1.5e3 Hz RMS) -- consistent with previous measurements
With PZT input to NPRO terminated (Attachment #1): 8.1e2 Hz/rtHz (3.5e2 Hz RMS)
Connected a terminated small box (we see in Attachment #1) before NPRO PZT: 6.3e2 Hz/rtHz (2.7e2 Hz RMS)
Connected input terminated Thorlabs PZT driver (MDT694): 5.9e2 Hz/rtHz (2.6e2 Hz RMS)
Connected input terminated summing amp (Attachment#2): 4.4e2 Hz/rtHz (1.9e2 Hz RMS)
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=-10dB, C1:PSL-FSS_FASTGAIN=-10dB): 3.9e3 Hz/rtHz (1.7e3 Hz RMS) -- consistent with "BEATX free (PSL free vs Xend free)" measurement
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=-10dB, C1:PSL-FSS_FASTGAIN=+10dB): 7.6e3 Hz/rtHz (3.3e3 Hz RMS)
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=+4dB, C1:PSL-FSS_FASTGAIN=+19dB): 2.9e4 Hz/rtHz (1.3e4 Hz RMS) -- Nominal gains when IMC is locked; consistent with "MC_F" measurement 40m/17458
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=+19dB, C1:PSL-FSS_FASTGAIN=+4dB): 1.1e4 Hz/rtHz (4.8e3 Hz RMS)

Discussion:
- Connecting TTFSS increased 60 Hz frequency noise, which suggests that TTFSS is creating this 60 Hz frequency noise.
- Setting TTFSS gains to nominal gains to IMC locked, 60 Hz frequency noise matched with frequency noise measurement using MC_F. This quantitatively supports that TTFSS is creating this 60 Hz frequency noise.
- Increasing C1:PSL-FSS_MGAIN and reducing C1:PSL-FSS_FASTGAIN reduced 60 Hz frequency nosie. This means that some portion of 60 Hz noise is from between these two gains.
- Note that having 60 Hz noise in TTFSS does not necessarily mean that our YARM noise is limited by this, because IMC loop suppresses the TTFSS noise. Assuming all 1.3e4 Hz RMS is all from TTFSS noise, it is suppressed to less than 1.3e4 Hz RMS/2e5 = 6.5e-2 Hz RMS (where 2e5 is IMC loop gain without super boosts, but it is actually higher with them) as frequency noise we see in YARM. YARM noise is measured to be 6.5e2 Hz/rtHz (2.8e2 Hz RMS), so it is not limited by TTFSS noise.
- Also dark noise measured at MC_F (1.2e2 Hz RMS) tells you that the dark noise is not limiting the frequency noise we see in YARM.

Touching various parts around TTFSS:
- We moved on to touch various parts around TTFSS to see if 60 Hz noise reduces in MC_F. We removed unused cables around TTFSS interface, touched power cables into TTFSS (both at TTFSS interface in the rack and TTFSS box on PSL table), BNC cables into TTFSS, disconnected slow controls, tried to avoid grounding of cables going into EOM (there is a small box that sums FSS feedback signal and 33.5 MHz; Attachment #3), but 60 Hz noise we see in MC_F didn't change significantly.

Next:
- Check grounding situation around TTFSS box.
- Check IMC length noise and error point noise by monitoring BEATX.
- Check coil drivers for MC1, MC2, MC3 by disconnecting drivers while IMC is locked.
- Try feeding back IMC servo also to MC2 with 60 Hz resonant gain to cancel 60 Hz noise

Note added at 23:50 to clarify:
nIMC : IMC length noise in frequency
nPSL: PSL free run noise in frequency
ne: sensing noise in frequency
nf: feedback noise in frequency
G: IMC loop gain (estimated to be 2e5 at 60 Hz without boosts)

MC_F = G/(1+G) * (nIMC + nPSL + ne + nf) + [noises in MC_F DAQ]
= 2.2e4 Hz RMS
MC_F when dark, MC servo nominal gain = G * ne
= 1.2e2 Hz RMS
PSL frequency noise after IMC lock = G/(1+G) * (nIMC + ne) + 1/(1+G) * (nPSL + nf)
YARM = [PSL frequency noise after IMC lock] + [noises from YARM loop]
= 2.8e2 Hz RMS
BEATX when PSL is free run, TTFSS low gain connected = nPSL + [noises from Xend AUX and BEATX sensing]
= 1.7e3 Hz RMS
BEATX when PSL is free run, TTFSS nominal gain connected = nPSL + nf + [noises from Xend AUX and BEATX sensing]
= 2.9e4 Hz RMS
BEATX when IMC is locked = [PSL frequency noise after IMC lock] + [noises from Xend AUX and BEATX sensing]
= 3.8e2 Hz RMS

So, our estimate is
ne ~ 1.2e2/G Hz RMS (small)
nPSL ~ 1.7e3 Hz RMS
nf ~ 2e4 Hz RMS (this dominates MC_F, but already suppressed enough in [PSL frequency noise after IMC lock])
[PSL frequency after IMC lock] ~ 3e2 Hz RMS (this dominates YARM and BEATX when IMC is locked)
nIMC ~ 3e2 Hz RMS (this dominates [PSL frequency noise after IMC lock])

Attachment 1: NPROandSmallBox.JPG

Attachment 2: TerminatingSummingBox.JPG

Attachment 3: EOMSmallBox.JPG

17459

Thu Feb 9 11:07:38 2023

Adding callibration filters to c1sus

CDS

Today I updated the ETMY suspension model to include 4 new filters at the output of the position, pitch, yaw and side summers and before the "To Coil Matrix". The library that was changed and updated is "sus_single_control_new". These callibration filters are labeled in the orange box as POSCAL, PITCAL, YAWCAL, and SIDECAL. The four filters are important as the will allow us to callibrate the position and side from counts to micro meters, and pitch and yaw from counts to micro radians.

The next steps for utilizing this update will be

- create a few experiments to find the callibration constants for the 4 degrees of freedom

- edit and update the ETMY Suspension screen to include selectable filter boxes to implement the callibration constants

For future reference, preform the update and restore the models to their previous states you may use the following:

to install the models we ssh into the computers running the ETMY suspension models (for example)

ssh c1sus

then for each model using the suspension library (we used c1sus c1mcs c1scx c1scy c1su2 c1su3) do

rtcds build-install c1sus

the watchdogs will need to be shut down for c1sus and the model will need to be restarted next

rtcds restart c1sus

Now we restore the filter values to the last saved point (about an hour before the update) in cds folder

python burtRestoreRTSepics.py -m c1sus c1mcs c1scx c1scy c1su2 c1su3 -o 10

Last we reset the watchdogs again using the following script in SUS>medm

python resetFromWatchdogTrip.py MC1 MC2 MC3 BS PRM SRM ITMX ITMY ETMX ETMY

17458

Thu Feb 9 10:19:22 2023

60 Hz noise investigations around IMC, part 4, using ALS BEAT

[Anchal, Yuta]

Yesterday, we have measured the frequency noise of PSL with IMC locked/unlocked using ALS BEATX/Y to narrow down where the 60 Hz is coming from.
All the measurements so far is consistent with a hypothesis that 60 Hz noise injected after MC_F is picked-off (it could be from MC_F DAQ readout or something in the IMC loop).

Method:
- Measured YARM noise spectra when YARM is locked with POY11 to measure the frequency noise with respect to YARM, and compared with MC_F
- Measured ALS BEATX and BEATY spectra when PSL is free running and when IMC is locked. Here, when "PSL is free running" is done with PSL shutter closed, but all the cables remained the same and FSS loop was in "down" state. Shutters at both ends were closed, and PZT inputs to AUX lasers were terminated to avoid noise injection from PDH locking with dark noise (this was necessary to reduce noise in BEATY).

Result:
- Attachment #1 is YARM noise calibrated into Hz, and Attachment #2 is BEATX and BEATY spectra with PSL free running (solid lines) and IMC locked (dotted lines). Below are summary of noise level at 60 Hz (RMS is calculated using a bandwidth of 0.187493 Hz)

YARM (PSL locked vs Yarm): 6.5e2 Hz/rtHz (2.8e2 Hz RMS)
MC_F (sum of noises in IMC loop): 4.9e4 Hz/rtHz (2.2e4 Hz RMS)
BEATX free (PSL free vs Xend free): 3.3e3 Hz/rtHz (1.4e3 Hz RMS)
BEATX locked (PSL locked vs Xend free): 8.8e2 Hz/rtHz (3.8e2 Hz RMS)
BEATY free (PSL free vs Yend free): 1.6e4 Hz/rtHz (6.9e3 Hz RMS)
BEATY locked (PSL locked vs Yend free): 1.5e4 Hz/rtHz (6.5e3 Hz RMS)

Discussion:
- "BEATX locked" measurement suggests that PSL locked to IMC (and Xend free) has noise less than 3.8e2 Hz RMS. This is roughly consistent with YARM measurement of frequency noise, and suggests that Yarm is stable enough to measure the PSL locked frequency noise.
- "BEATX free" measurement suggests that PSL free run (with cables connected) has noise of 1.4e3 Hz RMS (note that Xend free is less than 3.8e2 Hz RMS).
- MC_F measurement is the sum of noises in IMC loop, including IMC length noise + noise injected at error point (3.8e2 Hz RMS), PSL free run noise (1.4e3 Hz RMS), noise injected at feedback. Therefore, this suggests that 2.2e4 Hz RMS we see in MC_F is from noise injected after MC_F pickoff point (or in the MC_F DAQ readout).
- BEATY having large 60 Hz noise probably comes from noise in the beat measurement.

Next:
- Use BEATX to monitor 60 Hz noise.
- Try terminating PZT input to see if 60 Hz noise reduces. Try different gains at different point of MC servo board and TTFSS when IMC is unlocked to see where exactly 60 Hz noise is coming from.

Attachment 1: YARM_calibrated_noise_20230208_Hz.pdf

Attachment 2: BEATX_BEATY_MCF.pdf

17457

Thu Feb 9 10:05:37 2023

c1sus2 all FE models crashed spontaneously again

CDS

I just noticed that c1sus2 crashed again. Following 40m/17335, I fixed it by running

controls@c1sus2:~$ rtcds restart --all

"global diag reset" made all FE STATUS green.
Burt restored at 2023/Feb/8/19:19 for c1sus2 models.
Watchdogs reset for BHD optics and now all look fine.

17456

Wed Feb 8 12:25:42 2023

YARM WFS Loop Step Response

I did a quick step response test today with YARM WFS loops running. Steps were put in as offsets in channels C1:SUS-I/ETMY_ASCPIT/YAW_OFFSET to not let transmission go below 0.6-0.7 out of 1. I waited 30 seconds between each step by simply running sleep 30 on my terminal. Once finished, dtt still was taking a long time to get recently measured data even for 16 Hz channels. I used cdsutils getdata to get the measurement and calculate time constants for each loop. Time constant is defined by the time it took for C1;SUS-I/ETMY_ASCPIT/YAW_OUT16 channel to come to 1/e of the offsetted value. Inverse of this time constant is also printed as text on the plot. Note that I redid step on ETMY PIT as the first pass seemed not strong enough to me. See attachment 2 for settings.

The Pit loops seem to be bit faster with about 5s time constant while YAW loops have about 10s.

Attachment 1: YARM_WFS_Loop_Step_Response_1359920994.pdf

Attachment 2: Screenshot_2023-02-08_12-30-21.png

17455

Tue Feb 7 20:10:05 2023

60 Hz noise investigations around IMC, part 3

[Anchal, Yuta]

We have measured OLTF of IMC loop, and revisited IMC error point calibration again.
Also, we have tried to break the ground loop between MC servo board and TTFSS, but didn't help.

IMC OLTF measurement:
- IMC OLTF was measured using SR785 at TP1A and TP1B. MC servo board settings are the following.
- +4 dB in IN1
- 40 Hz pole, 4000 Hz zero filter was on
- 0 boost
- Eye-ball fit of OLTF gives zeros at [30e3,30e3] Hz, poles at [40,3e3,3e3] Hz (Attachment #1). 40 Hz pole is from 40:4000 Hz fiter in MC servo board and 4kHz zero is compensated by IMC cavity pole (~ 3.79 kHz). We are not sure where two 3k:30k are from.
- Anyway, eye-ball fit gives OLTF gain of 1.7e5 at 60 Hz, which is accidentally roughly the same as previous estimate (40m/17446).

Revisiting IMC error point calibrations:
- We realized that error signal calibration of 13kHz/V a while ago in 2018 (from 40m/14691, which is from 40m/13696) is a calibration for IN1.
- So, 70 uV/rtHz at 60 Hz at TP1A corresponds to 70 uV/rtHz / 4dB / (4e3/60) * 13kHz/V = 0.009 Hz/rtHz, which corresponds to 1.2e-15 m/rtHz.
- The estimated frequency noise at the output of IMC in terms of arm length is 1.2e-15 m/Hz * (1+G) = 2.0e-10 m/rtHz (or 1.4e-10 m RMS considering 0.5 Hz bandwith).
- Noise measured with the same condition but PSL shutter closed was 7 uV/rtHz at 60 Hz (40m/17431). This correspond to 1.2e-16 m/rtHz (or 8.5e-17 m RMS), which is an estimated dark noise.

Summary of frequency noise measurements at 60 Hz:
- 1.4e-10 m RMS (or 1.0e3 Hz RMS) as measured at TP1A (estimate of unsuppressed noise difference between IMC and PSL)
- This being smaller than MC_F measurement is strange, as this should be an estimate of total unsuppressed noise (if 60 Hz noise is coherently cancelling each other, this can be explained).
- 3.1e-9 m RMS (or 2.2e4 Hz RMS) as measured at MC_F
- 4.3e-11 m RMS (or 3.1e2 Hz RMS) as measured using XARM and YARM
- 1.8e-10 m RMS as measured using FPMI DARM

Buffering MC servo board output to TTFSS:
- We have inserted a battery-powered SR560 in between MC servo board output to TTFSS, trying to break the possible ground loop between 1X2 rack and PSL.
- To do this, we had to lower IN1 gain to -6dB, to avoid saturation of SR560.
- This didn't make any difference in MC_F or POY during YARM lock.

Attachment 1: IMC_OLTF.png

17454

Tue Feb 7 11:12:44 2023

rana

YARM WFS First Attempt - Success

It would be great if you could calibrate these ASC channels into physical units (e.g. urad or nrad). I am curious to see how the noise spectra compares to the IMC WFS.

Since the data is still on disk, you can probably use the oplev channels to calibrate the WFS. Also, you can calibrate either WFS or oplev by moving the SUS alignment sliders until the arm power goes down by sqrt(2) or 2.

To get data faster with DTT, I ask only for data sampled at 16 Hz. You can either just read the EPICS channels (OUT16) or ask DTT for a BW=16 Hz for the fast channels. No need for high sample rate for step response plots.

17453

Mon Feb 6 20:44:34 2023