Nishino

This is a continous work of 3700.

I measured the beam profile of the Prometheus (auxiliary) and Mephisto (main) laser. Layout can be found in Fig. 1 and 2.

Fig 3 and 4 are the profile of the main and aux lasers. The main profile was measured on 2024.9.13. 

Origins of z coordinate are labeled in Fig. 1 and 2.

As mentioned in 3700, the profile of prometheus laser is very dirty, which makes it har to fit the propagation with gaussian propagation beautifully (Fig. 4).

Nishino

This is a continous work of 3707.

I measured frequency response of the PFD circuit (in 3707 we reported phase response). Input volatages are 1 Vpp for both two inputs. LO is fixed to 125 MHz sine wave, while RF side is scanned from 1 MHz to 250 MHz.

As shown in Fig.2, the output signal (=error signal) crosses zero when RF frequency matches with LO frequency. It is confirmed that this circuit can be used for PLL.

Aso, Shalika

The circuit was finalised to be made for EOM. The simulation was done in LTspice. We almost have all components in elec shop. 

It was taken care that impedance is matched between source(moku) and circuit using OpaAmp. The OP27 planned to be used should have output current max as 30mA. 

The EOM will have

1. Moku will provide 0.1 V

2. Resonant frequency of 979.2 KHz. 

3. Gain is around 3.01k

4. Output current of Op27 is 24.2 mA

5. Matched imepdance is around 49.5 ohm.

Fig 1 shows the circuit diagram and Fig 2 shows the transfer function plot. 

The datasheet of OP27 for reference.

Nishino

This is a continous work of 3734.

I measured the actuator efficiency (A) of the piezo-atattched mirror with a Michelson interferometry(img0959.jpg, layout.png). The result is: there still exists resonance around 660 Hz, which prevents to increase UGF.

1) Setup

Optical setup is a simple Michelson. One mirror is the PCM and the other is a super mirror with the same curvature. The piezo is connected to a voltage amplifier (*10 in amplitude), which is connected to the output port of the filter F (Moku:Go). F is a first-order filter shown in filter.png. The interferometer is locked in mid-fringe. The output (Vout) is fedback to the piezo (diagram.png).

2) Estimation of the optical gain (H)

Scanning the Vin over a fringe, one can estimate the optical gain (H) of the system. One fringe takes 1.33*10 V to the piezo (mokuoscilloscopedata20240918145453screenshot.png), which means:

H = 532 nm/(13.3 V) ~ 4e-8 [m/V] = 40 [nm/V]

In spec, PA44LEW has an efficiency of 2.6 um/150 V = 17 [nm/V], which is lower than the measured value. 

3) Open loop transfer function (OLTF)

OLTF is shown in OLTFandAH10.png. There still exsists peaks around 660 Hz. This prevents to expand the UGF.

4) Estimation of the actuator efficiency (A)

A.png is the actuator efficiency. It is flat at low frequencies but has a structure around 600-700 Hz. This is an independent result that shows an oscillating mechanism in the piezo-bonded PCM.

5) Discussion

According to Akutsu-san and Takano-san, steering mirrors with springs for adjustment have resonance around 500 Hz. Their suggestion is to mount the PCM to a solid mount without steering and prepare another mirror only for alignment. This hypothesis can be checked by replacing the current mount to a different one and see if the resonant frequency shifts.

HWP was installed. Measurement file is as follows

Using calibration file 1:

 C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Retarder\HWP\20240917\0 deg\Arbitrary Pol\Thu, Sep 19, 2024 3-00-50 PM.txt

Using calibration file 2 (linear Polarizations):

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Retarder\HWP\20240917\0 deg\Linear Pol\Wed, Sep 18, 2024 6-24-03 PM.txt

The retardation and diattentuation calculation using homogeneous JM formula and weakly Polarizing JM formula, do match though. 

There is a major difference between birefringence extraction from a weakly polarizing jones matrix and a homogeneous jones matrix. A weakly polarzing element jones matrix can be inhomogeneous and yet meet the condition of weakly polarzing element  (which is jxx-1, jxy, jyx, jyy ~ 10^-4) . Its good practice to not confuse both. 

Eg:

A homogeneous weakly pol. JM: J = np.array([[1+1E-4, 1E-4], [1E-4, 1+1E-4]]), with eta = 0

A inhomogenous weakly pol. JM: J = np.array([[1+1E-4-7E-5, 1E-4-9E-5], [1E-4, 1+1E-4]]), with eta = 0.69

Both meet the requirement of weakly polarizing element condition. Yet you might go the wrong way in classifying them if you just consider homogeneous and inhomogeneous criteria and get misleading results. 

Nishino

The IR side of the Prometheus laser has a strange mode, splitting like TEM01 mode. The spec sheet says TEM00 with M<1.2.

We attenuated the laser power with two mirrors, (R>99.97 % and R>98.5 %), and rejected the GR beam which somehow copropagate with the IR. 

The report is attatched in pdf file.

The linear input polarization states were filtered from the 1st calibration file. The condition was abs(ellipticity)<=2 degree. there was 145 sets of voltages.

voltage file name: C:\Users\ssing\Dropbox\LC-Experiment\Measurement Data\Scan voltage\LinearPol_20240917

2nd calibration with only linear Pol voltages (5 iterations, 100 averaging). Total Measurement time is around 25-30 mins. 

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\20240917\Tue, Sep 17, 2024 6-51-22 PM.txt

Both the files are used to preapre results for comparing the reconstruction of birefringence from linear and arbitrary polarization states.

I have also placed the empty rotator mount  before the camera before the calibration to avoid any issue of interfering with the setup later. The HWP can later be mounted directly.

To address the issue mentioned in elog 3735, I am re-measuring the HWP

Since there is no place between the BS and AlGaAs coating to put both camera and HWP. I have place the polarization camera in the reflection of the BS and put beam dumb in transmission. This avoids removal of the AlGaAs and the issue of its realignment.

The measurement will begin from calibration in reflection of BS and then putting HWP in between camera and BS.

The voltage of LC = 0-3.5V with 0.1V step and 100 avg. The measurement will start after warm up time of 30min.

calibration file:

1. C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Retarder\HWP\20240917\0 deg\Tue, Sep 17, 2024 10-17-41 AM.txt        C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\20240917\Tue, Sep 17, 2024 11-53-11 AM.txt

The RF circuit deisgn was truned to obtain impedance of around 50ohm. This will match the impedance of circuit with Moku and not break it, at resonant frequency. Usually, the imepdance mis-matching will cause issue if you use wires longer or same order or magnitude as your resonant frequency, as wave properties start coming into play. 

Our resonant freq is 7MHz. The analysis was done is LTspice.

For our case, we have used an Opamp circuit to match impedance. 

Fig 1 is the circuit diagram

Fig 2 is the transfer function 

Plot a: V(output)/V(input) magnitude and phase

Plot b: V(input1)/I(input1) imepdance at the input (magnitude and phase) respectively

plot c: real(V(input1)/I(input1))

plot d: imaginary(V(input1)/I(input1))

Fig 3: Smith Chart

There seems to be some discrepancy between power observed without sample(HWP) and with Sample(HWP). 

The power (normalised with main laser power) with sample / The power (normalised with main laser power) without HWP is shown in Fig 1 . It basically is the gain of the optical system which is transmitted power divided by the incident power.

Both the measurements were taken in a few days gap(~4-5 days). The normalization should have taken care of the laser power fluctuation. But, for some reason, the gain of the optics is more than 1. It could be arising from some inconsistent laser power increment or some very lossy optics before power meter to observe the main laser power. It could also be that the number lies within the uncertainity of the system.

The delta=det(J^+ J) and max intensity gain plot(of the HWP jones matrix) without considering the power factor in jones vector and without normalization is shown in Fig 2. 

This is a continous work from 3717 (date: 2024.09.06)

I locked the PCC with GR laser by feeding back the signal into frequency actuator of the laser. The locking was stable, no weird behaviour at 667 Hz. The firt png is the open loop gain.

Still 667 Hz peak exists (second png). I guess this peak originates from the piezo actuator, hindering feedback locking at the same time. I will try bonding again.

[Marc, Shalika]

We installed the 30mm diameter sample.

map with sample taken with 2 mm step size and 15mm radius

below files sorted from input linear polarization angles of 0 to 75 with 15 deg increment.

Input_filenames = [ 'Mon, Sep 9, 2024 3-16-23 PM.txt', 'Tue, Sep 10, 2024 10-52-14 AM.txt' , 'Tue, Sep 10, 2024 12-39-57 PM.txt' , 'Tue, Sep 10, 2024 1-20-39 PM.txt' , 'Tue, Sep 10, 2024 2-08-09 PM.txt' ,'Tue, Sep 10, 2024 3-19-48 PM.txt']

Output_filenames = [ 'Mon, Sep 9, 2024 3-40-50 PM.txt', 'Tue, Sep 10, 2024 11-53-20 AM.txt' , 'Tue, Sep 10, 2024 12-46-08 PM.txt' , 'Tue, Sep 10, 2024 1-26-27 PM.txt' , 'Tue, Sep 10, 2024 2-13-50 PM.txt' , 'Tue, Sep 10, 2024 3-19-48 PM.txt']

The spec sheet for the 88 MHz EOM says to apply about 12-15 dBm to get near 0.2 rad modulation depth. I swapped DAC0 (-9 dBm) and DAC1 (8.2 dBm) and plugged DAC1 into +14.1 dB RF amp. I intended to use +14 -12 to achieved 12 dBm RF injection but somehow it only came out of theRF amp as 11 dBm without any attenuator. DAC0 is also amplified ~ 14 dB and sends 4 dBm to the splitter for SHG and IRMC LO.

The SHG has a reasonable error signal and locks, but has oscillation even near zero gain. The IRMC has some visible RF sidebands in the reflection PD (approximately 3% of carrier on each side) but the PDH error signal is quite small. Turning the lock switch on the IRMC servo does nothing, it doesn't even disrupt the spectrum.

I should check internal connections.

The SHG/IRMC EOM modulation is too low. The channel DDS1 DAC0 produces only -9 dBm RF power, which gets amplified to 5 dBm from the RF amplifier rack. The nominal value to be used for the EOM is 25 dBm.

I could see the IRMC PDH error signal with the familar shape from far-detuned RF sidebands, however, the signal strength of the PDH is extremely weak. I suspect this is also the reason behind the SHG/GRMC weak lock, however in the case of the SHG the input IR is 900 mW (vs 3.5 mW for IRMC) so maybe some signal can be seen despite weak modulation.

I think a temporary fix is to use DDS1 DAC1 (SHG/IRMC demod), which outputs 10 dBm, and amplify to send to the EOM. Then amplify DDS1 DAC0 + 14 dB and split into demodulation signal. This will give ~ 2.5 dBm for each demodulation signal.

I had noticed the weird electronics settings problem for the SHG and GRMC servo gain after Mitaka campus was struck by lightning in late July. Perhaps that was also connected to the RF signal generation issues.

Moku was setup to be  interfaced over usb. Connect the green one using localhost:8091

In windows powershell

netsh interface portproxy set v4tov6 listenport=8091 connectaddress=['moku-ip'] connectport=http

PS: The black one has port 8090

Measured noise of the PD and moku. The pd was connected to the CH1 and Moku CH2 was terminated with 50ohm. The Moku:Go spectrum analyzer was used to get the spectrum with 100 avg, and hamming window.

PD: PDA05CF2 : CH1 (red plot)

Moku:Go : CH2 blue in color

Fig 1: With power supply to PD off

Fig 2: With power supply to PD on