[Aritomi, Matteo]

Recently we had a problem that QPD2 DC centering loop cannot be locked.

Today we found that when we move the green beam horizontally, QPD2 DC signal somehow moves vertically and vice versa. This means horizontal and vertical correction signals for QPD2 galvo should be swapped. After we swapped the horizontal and vertical correction signals, QPD2 DC centering loop locked stably even when the green is reflected from filter cavity. Maybe the cabling of QPD2 is wrong.

[Aritomi, Yuhang]

We measured homodyne AR reflection and it is around 4 uW while LO power is 840 uW. It means we have 0.5% loss for each homodyne PD. In total, we have 1% additional loss from homodyne AR reflection.

I re-installed Q-mass in order for checking of operation.
Tomorrow, I will evacuate the chamber and confirm the operation of Q-mass and vacuum gauge.

Aritomi and Yuhang

According to elog 1659, the simulation result of beam size and gouy phase for AA system is shown in the attached figure 1. We could see that there is only 1000mm lens and QPD1 is located close to beam waist while QPD2 is located far from beam waist.

The measurement was done recently to check the real beam size. The measured points and beam diameter is shown in the attached figure 2. The measurement done for QPD1 (9 points) is indicated by 'cross' wihle the measurement done for QPD2 (3 points) is indicated by 'point' 21,22,23.

Since the beam size should be symmetric for two path after BS, the 'cross' and 'point' can be imagined to be located in a single beam. These measured ponits are fit with gaussian beam as shown in figure 3. The measurement done for QPD1 and 2 seems to have a wrong distance, we will check that.

[Aritomi, Yuhang]

Yesterday we tried many galvo servos for QPD2 DC centering, but no galvo servo can lock QPD2 DC centering loop. WFS2 DC signal either oscillates or goes away when we tries to lock.

We found that QPD2 DC signal moves a lot compared with QPD1 (attached movie). This may be due to larger beam size at QPD2 (farther from waist position). We measured spectrum of QPD DC signals without DC centering loop (attached screenshot). QPD2 DC signals are larger than QPD1 by a factor of ~2.

We also characterized beam size of green around QPD1 and QPD2 (Yuhang will report).

Today, I soldered another temperature sensor.
Then I tried to install the Q-mass, but it was not successful due to the weight of Q-mass...

Anyway, I will order indium sheet or Apiezon N Grease in order for thermal contact.

[Aritomi, Yuhang]

We measured sensing matrix of WFS1. We injected a line to pitch and yaw of input mirror. The frequency of the injected line was 12 Hz and the amplitude was 2000. Then we measured WFS1_PIT and WFS1_YAW signal.

First we injected a line to pitch of input mirror and measured 12 Hz peak of WFS1_I_PIT and WFS1_I_YAW with demodulation phase R = 90 deg. With R = 90 deg, WFS1_I and WFS1_Q signals were almost the same. The measured 12 Hz peak is as follows.

This means we have about 10% coupling from pitch to yaw of input mirror. This may be due to coupling of coil-magnet actuator driving.

Then we optimized the demodulation phase R in order to maximize WFS1_Q_PIT signal. The optimal demodulation phase for WFS1_Q_PIT was R = 20 deg. After that we injected the same line to yaw of input mirror and measured WFS1_I_YAW and WFS1_Q_YAW. Measured sensing matrix of WFS1 for pitch and yaw with demodulation phase R = 20 deg is as follows. Screenshots of the 12 Hz peak for PIT and YAW are also attached.

The optimal demodulation phase R = 20 deg for pitch was not exactly optimal for yaw, but it seems we can use WFS1 Q phase signal for both pitch and yaw.

We'll replace galvo servo for QPD2 and measure sensing matrix of WFS2.

What I did

I replaced the vacuum gauge which was repaired by the company as attached picture.
Then I installed a temperature sensor.
First, soldered the connector to the controller.
Then I soldered a sensor to the cable inside the cryostat.

After that, I checked the temperature which was displayed on the controller.
The value was about 430 K and was strange.
I suspected that there was a contact failure at some point.

Eventually, it was due to the poor connection between the cable and the pin.
After solving this problem, the displayed value was reasonable as shown in the attached picture.

Next step

I will install another temperature sensor and Q-mass.
And then I will start cooling down.

Shimode-san, Miyakawa-san

After experiencing the failure of AA channels and PSD reported in entry #2096. We shipped the PSD and its power supply to Kamioka where Shimode-san investigated the circuits.

His report is reported below (the japanese version is in the attachments):

1. Features of 100V of NAOJ power supply
3pin Earth terminal: Earth line connected to cold and grounded into earth through the power distribution. (Pic 6. "100v_Earth.jpg")
3pin Cold terminal: Power output connected to Earth on the power distribution. (Pic 5. "100v_Cold.jpg")
3pin Hot terminal: Power output not connected to Earth on the power distribution. (Pic 7."100v_Hot.jpg")
* Note that the tester voltage is based on the Earth (rack) of the building. (pic 3. Earth_point.jpg)

2. Features of connection between PSD and power supply
(1) The PSD chassis is connected to the power supply chassis by a shield on the power connection cable. As a result, the PSD chassis and the power supply chassis have the same voltage.
(2) The NAOJ power supply's GND (black) is isolated from the power supply chassis. Therefore, the PSD chassis and the PSD board are at different voltage levels from the PSD's GND.
(3) The voltage difference between the NAOJ power supply's GND and the 3pin 100V power supply's ground terminal is about 21V! or 1V depending on the way to plug to AC100V power (forward and reverse). (pic.1, pic.2  "100vON_A.jpg" "100vON_B.jpg)

3. GND in each chassis.
(1) About PSD output
As shown in "PSD_connector.jpg", the outer of LEMO is GND because of the unbalanced output. If conversion to BNC without connecting to chassis GND, the voltage at "2. (3)" is applied to both positive and negative.
(2) BNC to Dsub chassis   
BNC is from parallel input to Dsub parallel output. GND is not connected in the chassis. (See https://gwdoc.icrr.u-tokyo.ac.jp/DocDB/ 0047/D1604782/001/BncDsub_ADC.pdf )

(3) About AA/AI Chassis
The 5pin of Dsub INput in the AA/AI chassis is not connected. (The AA/AI chassis is designed to use the power supply's GND connection.)
  (See https://gwdoc.icrr.u-tokyo.ac.jp/DocDB/ 0099/D1909971/001/ADC_AA_interface.pdf )
  (See https://gwdoc.icrr.u-tokyo.ac.jp/DocDB/ 0099/D1909969/002/AA_AI_Filter.pdf )
  * The new AA/AI Filter Board has a 5pin connection, but the 5pin is disconnected on the interface board.

4. From the above
The GND among PSD → BNC-Dsub → AA/AI Interface Board → AA/AI Board is not connected. As a result, a large voltage difference can happen between [GND of PSD] and [GND of AA/AI circuit].
It is presumed that the very high common-mode voltage originating from the power supply (from noise around) is applied to the AA/AI board and the first stage ICs are all damaged.
In addition, I guessed that the high voltage from the power supply, GND and Earth went to AA/AI input, but the same things can happen even if different voltages are applied to the power supply chassis, power supply cable or circuit configuration chassis due to other factors.

5. Solution.
Temporal solutions: (1) Pull the GND line from the GND (black wire) inside the power supply, and connect to the GND(0V) of DC power supply supplying the AA/AI along the signal line. (2) Connect the ground wire between the "PSD chassis + NAOJ power supply chassis" and the "AA/AI chassis".
Fundamental Solutions: (1) Use 15V power supply boards AEL made in all chassis. The power line should be along the signal line. (2) Connect the chassis and the rack to the GND (0V) of the power supply. (3) Connect the ground through wire between the PSD chassis and the AA/AI chassis. Connect them with a relatively thick wire. (4) Insulate the PSD from surrounding metal objects.

Matteo, Yuhang, Eleonora

We measured the QPD2 electronic noise with spectrum analyzer using 32 dB amplification. 

Pic1: Amplified QPD2 noise compared with 32 dB amplifier noise and spectrum analyzer.

Pic2: Same plot of entry #2121 where we added QPD electronic noise. Note that the data were divided by a factor 40 to subtract the 32 dB amplication used for the measurement. We didn't plot data below 1Hz as we assumed they are dominated by the spectrum analyzer noise.

We verified that the QPD measurement doesn't change when we added a bandpass filter (https://www.minicircuits.com/WebStore/dashboard.html?model=SIF-70%2B) before the 32 dB amplifier.

Yamamoto-san, Aso-san, Yuhang, Eleonora

Thanks to Aso-san's help Guardian PC is now connected to the TAMA DGS network. We used a USB-> ethernet adaptor since the system was not recognizing the ethernet port.

Aso-san solved also a problem caused by the fact that space on the disk was completely occupied by log files generated by an error.

Then Yamamoto-san could remotely access the PC and set up the guardian. Below a memo of his work:

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Yuhang, Eleonora

Pic.1 shows the QPD2 (seg 1) signal for FC (oplev OFF), aquired with DGS and spectrum analizer respectively for 1.5 mW sent on QPD

Pic.2 shows the QPD2 (seg 1) signal for FC (oplev OFF), aquired with DGS and spectrum analizer respectively for 2.5 mW sent on QPD

We checked that the QPD dark noise is below the spectrum analyzer noise.

# About green power to FC

In order to have more light on QPD we increased the light injected into FC by incresing modulation amplitude of AOM/ ( from 2.5dBm to 5.5dBm).

The green refleced light when FC is locked is about 1/4 of the input light. The reflected light is splitted by a BS (92:8) and 92% is send to QPDs and 8% is sent to FC lock PD. (note that an additional attenuation of a factor 3 is present before the PD)

The usual amount of light sent to FC is ~14.5 mW, the maximum we can send is ~25 mW. The limitation is due to 78 MHz EOM damage threshold.

Here the two cases corresponding to the shown measurement:

Yuhang, Eleonora

We installed 12 dB attenuator on the LO of the QPD2 demodulation board, as we did for QPD1 demodulation board 1 (see entry #2112)

We performed the same test and confirmed all the channels are working fine.

The LO was -6dBm, we notice that if we put additional attuantion the demodulated signal is slightly increased. For a LO of -21 dBm the demodulated signal reaches the maximum amplitude and it is a factor 1.2 higher that in  -6dBm case.

Anyway we will split -6dBm LO between the 2 demodulation boxes. The actual LO for each board will be -12dBm which is fine.

Yuhang, Eleonora

We report three additional failures of Anti Aliasing (AA) channels.

Symptom: ADC channel reads large, almost constant offset (order of ~1000 counts). The offeset is still present if we disconnect cables towards AA board -> it is not coming from the BNC2Dsub converter. The offset is reduced when we switched off AA board and disappear when we disconnect AA from ADC. 

This time the broken channels are:

- Ch.10 of AA0 used for INPUT YAW OPLEV (We realized it while charachterizing input oplev on 13/07)

- Ch.16 of AA0 used for END L SUM  OPLEV (not currently used, we know it is broken since several months)

- Ch.14 of AA1 board, used for  WFS2 Q3 (We realized it while charachterizing demodulators on 10/07)

For the moment I rearranged the model to used spare Anti Aliasing channels  for INPUT YAW OPLEV (chan 9-12 of AA0 moved to chan 25-28 of AA1).

We shoud understand the origin of such problem and solve it. According to Miyakawa-san It might be due to a ground-connection issue in the design of KAGRA Bnc2Dsub converter JGW-D1604781 https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=47

Eleonora and Yuhang

To have an idea about how much amplification is required for demodulated signals from QPD, we compared the QPD demodulated signal with DGS and network analyzer.

The test is done by taking signal from QPD2 segment1 with green beam reflected form the locked filter cavity. The beam was centered with galvo on the QPD and power was ~1.5mW

In the first attached figure, the in-phase demodulated signal (measured in DGS/network analyzer) is shown together with DGS ADC noise. We  see that the measurement in DGS and network analyzer agree with each other. However, in the measurement of DGS, the peaks are barely higher than the ADC noise.

In the second plot, there is a comparison of demodulated in-phase/in-quadrature signals.

The large peak at 88 Hz is due to galvo loop, we adjusted the gain of galvo  servo and it is reduced.

Yuhang, Eleonora

Some measurement on the local control noise was done, in order to compare their performamces to those of AA. 

This is for the input mirrors. The calibration in rad/count is (reported in entry #1874) used for this measuremnt is:

We recall that that Input and end mirrors oplev use commercial PSD (thorlabs PDP90A) and the signal is amplified by a factor 100 with a SR560 and filtered with a 2nd order lowpass with cut-off frequency 100 Hz.

PIC 1:  Piitch signal compared with ADC noise and dark noise (the noise measured when the laser is switched. Factor 100 amplification from SR560 still present)

PIC 2:  Yaw signal compared with ADC noise and dark noise (the noise measured when the laser is switched off. Factor 100 amplification from SR560 still present)

PIC 3:  Piitch signal compared with ADC noise and signal withoud the factor 100 amplification (red curve should be multipplied by a factor 100 to have the good calibration)

PIC 4:  Yaw signal compared with ADC noise and signal withoud the factor 100 amplification (red curve should be multipplied by a factor 100 to have the good calibration)

Matteo, Eleonora

We test QPD1 demodulator after adding the 12 dB attenuator on the LO path (see elog #2106) and confirmed that all the 4 channels were working fine.

We sent a LO and RF signal from DDS (-6 dB both). LO was at 78 MHz and RF was at 78MHz + 100 Hz. We could correctly seeing a signal at 100 Hz after the demodulation, shifted by 90 deg in the I and Q output. (see pic).

We tested other offsets (from 1 Hz to 10 kHz). For all these values demodulated signal has a constant amplitude fase offset between I and Q is always ~90 deg. We verified this for all the 4 channels.

Matteo, Eleonora

We put a reflective mirror after green FI so that the light is reflected back to the QPD2 using the standard path. The power was changed acting on the AOM modulation amplitude. 78MHz and 87.6 MHz modulation are switched off.

Pic 1: RF output of QPD2 Seg 1 in with different power level. 

Pic 2: Same of Pic 1 but zoomed around 78 MHz.

Pic 3: Peak height at 15.2MHz and 30.4 MHz as a function of the green power. (This is a real signals come from PDH of SHG)

Pic 4: Noise at 20 MHz as function of the green power. 

Measured data are reported below:

We used the following setting :

RBW: 300kHz.  VBW: 10kHz

Average: 10

Internal amplifier: OFF

Spectrum analyzer attenuator: 10 dB

When measuring the peak hight we used different attenuation levels (20/30  dB) to avoid saturation

Yuhang, Eleonora

We changed the BS used to split the reflection of green FI FC lock PD and QPDs.

Before we were using a BS T 10 (70:30 for s-pol) and we replaced it with a BS X 10 (90:10 for s-pol).

Note that we are using p-pol so the actual ratios are different.

In the previous configuration we had 2 OD (0.5 and 0.6). Now we use only one OD (0.6) and the power is ~0.35 mW and the power reacing the pd is ~150 uW

We need to check FC PDH signal.

Yuhang, Eleonora

Pic 1: RF output of QPD2 Seg 1 in with different power level. 

The 15.2 MHz modualtion was switched off. The SHG was set on resonance manually. For each measurment we double-check that the power was stable.

We put a reflective mirror after Green FI so that the light is reflected back to the QPD using the standar path. The power was changed acting on the AOM modulation amplitude.

For 10 mW of  green power we measured 1.8mA

Pic 2: Same of Pic 1 but zoomed around 78 MHz.

Pic 3: RF output of QPD2 Seg 2 in with different power level. This time the 15.2 MHz modulation was switched on. The EOM RF driving signal was - 9dbm in this measurement. (Note that DDS output (-6dBm) is usualy amplified by 14dB and attanuated by -6dB, in this case we divided the DDS output by 8 in the software (corresponding to -9dB)). We want to confirm how much modulation depth are we using for 15.2 MHz EOM.  I put a curve with modulation switched on (P = 10 mW) for comparison. The stuctures are at harmonic frequencies of 15.2 MHz. It seems there is a quite strong saturation effect. This is strange becasue this effect was not observed in e-log #2067 when the 15.2MHz modulation was even higher (not dived by 8 inside DDS software). [UPDATE: we found this is due to saturation of the spectrum anlayizer internal amplifier which was off in the previous measurement]

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We used the following setting (see Pic4):

RBW: 300kHz

Average: 10

Internal amplifier: On

We found that electronicn noise on seg 2-3-4 is ~ -67 dBm while for seg 1 is ~ -69 dBm.