I also added a voltage regulator 7815 (for +15V) and 79 (for -15V) to supply voltage for opamp. A 0.33uF ceramic capacitor is added on the input side of these regulators. Another 0.1uF ceramic capacitor is added on the output side of these capacitors.

I can use a feedback resistance of 1.1k instead of 1.07k, since 1.1k is readily available. Also, the inductors measure about 6.4mH(using multimeter), instead of 6.8mH. In series they will be 12.8mH instead of 13.6m in the deisgn. This shifts the resonant frequency by 18kHz, but doesn't change the gain or the current properties of the circuit too much. So, even if the components will not be perfect we will not overshoot the 20mA limit of the opAmp current at the output.

The OpAmp in elec shop is Op27G / OP27 whose max current is 20mA. 

There is a discrepancy in the reported output current for OP27. Texas instruments says 30mA in their datasheet.  On the other hand Digikey reports 20mA. 

From last Friday

I previously attempted to lock the SHG by switching around the DDS1 DAC channels - in the normal configuration DAC0 outputs -9 dBm to +14 dB -> 5 dBm to main laser EOM, while DAC1 outputs 9 dBm to splitter for SHG/IRMC demod. I switched them around but this just makes the SHG oscillate even at 0 gain. So I put them back to normal. The rationale for switching is that the wiki shows an 88 MHz Qubig EOM datasheet which specifies that we need about 12-15 dBm RF power to achieve 0.2 modulation index. However, this is for the OPO EOM "EO-88K3-NIR", while the ML EOM is "PM8-NIR-88". I cannot find the datasheet for this particular EOM but other PM8 EOM datasheets indicate that 5 dBm is sufficient to generate 0.2 modulation index.

I measured the open loop transfer function EPS1/EPS2 of the SHG (fig 1, 2) and GRMC (fig 3, 4) using FFT mode of the spectrum analyzer and injecting about 100 mW noise to PERTURB IN. The coherence is basically 1 around the unity gain frequency. I also checked the SHG transfer function with swept sine mode and it gives basically the same result (fig 5). The SHG unity gain frequency is a bit low. Nominally it should be between 2-3 kHz (Aritomi thesis) but it sits about 1.6 kHz with 50 degrees phase margin when set to 0.09 gain. However, increasing the gain further past 0.1 makes the SHG oscillate quite a lot, even though the sticker on the servo says 0.2 indicating a former optimal setting. I set the GRMC gain to 0.8 which gives 3.4 kHz UGF with 45 degrees phase margin.

The GRMC error signal is clearly visible but also a bit noisy. It's quite curious that the GRMC signal shows up at 88 MHz (fig 6, 7), which is the modulation applied to the IR carrier, despite also propagating through three 1064 reflection dichroics. But evidently it has worked to lock the GRMC since the EOM replacement a while ago. I have a bit of difficulty in locking the GRMC to TEM00 though, a lot of the time it just locks to near zero transmission amplitude and I have to keep hitting the rest button a lot. when I managed to lock it with 4.2 MZ offset (stabilizing GRMC transmission to 25 mW) and noted the GRMC transmission level (GRMC TRANSMISS IN) of 316 mV. I set the GRMC threshold to about 100 mV which helps for avoiding HOMs but it's still not reliable for locking to TEM00.

The force constant k was evaluated as follows:

mg = kx

k = (delta mg) / (delta x) = ((0.06-0.03) * 9.8)/(0.01 * (28-27))  = 29.4

The retardation of the data was evaluated and plotted. We can see a linear dependency of retardation(effective and linear retardation) with the stretch of hydrogel. On the other hand, circular retardation and linear retardation along 45deg axis doesn't change.

The distibution of retardation was fit with gaussian fit and the mean and std was estimated. Then for each displacement the analysis was repeated to make the plot 1.

Plot 1 Retardation vs. Displacement

[Katsuki, Shalika, Marc]

The thickness of the hydrogel is 1.5mm. The measurement is taken with LC voltage from 0.5V - 3 V with 0.25V step and 10avg.

26.7 cm (F=0g)

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Wed, Sep 25, 2024 10-42-00 AM.txt

26.8 cm

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Wed, Sep 25, 2024 11-45-27 AM.txt

26.9 cm

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Wed, Sep 25, 2024 11-48-42 AM.txt

27 cm

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Wed, Sep 25, 2024 11-52-24 AM.txt

27.1 cm

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Wed, Sep 25, 2024 11-56-57 AM.txt

27.2 cm

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Wed, Sep 25, 2024 12-01-33 PM.txt

27.3 cm

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Wed, Sep 25, 2024 12-06-09 PM.txt

Hydrogel changed here.

27.4 cm (discarded for analysis)

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Wed, Sep 25, 2024 1-46-34 PM.txt

27.5 cm (discarded for analysis)

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Wed, Sep 25, 2024 1-52-02 PM.txt

The beam in the reflection of beam splitter was tuned to remove the misalignment of the beam (beam height was chaning by 1cm at the end of the table). Now the beam height is same as before the BS.

I placed the Shinkosha S7 after the beam splitter reflection and before the camera. The LC voltages are changed from 0.5V - 3V with 0.25V step size, with 10 averaging.

without sample

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\S7\Tue, Sep 24, 2024 3-23-26 PM.txt

with S7

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\S7\Wed, Sep 25, 2024 10-07-47 AM.txt

[Katsuki, Marc, Shalika]

A 1mm thin hydrogel was prepared between plates to measure its birefringence. We change the LC voltage from 0.5-3 V with step size of 0.25V and averaging  of 10th order.

without sample

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Tue, Sep 24, 2024 3-23-26 PM.txt

We try to shake the hydrogel to see if any movement due to air flow will change the output. The range of azimuth change is 0.02 deg and ell change is 0.1 deg. We then try to stretch the hydrogel using force gauge. The minimum reading of force gauge is 10g.

1. At, F = 10g

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Tue, Sep 24, 2024 3-27-28 PM.txt

It seemed there were issues related to the resolution of the gauge, and we weren't able to see anything other than 10. When we saw the force gauge reading of 40g, the hydrogel broke. We started taking measurements related to the position of the black actuator on the bar

2. 31 cm : C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Tue, Sep 24, 2024 4-02-55 PM.txt

3. 30 cm: C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Tue, Sep 24, 2024 4-22-05 PM.txt

4. 29.5 cm : C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\cell birefringence\hydrogel\Tue, Sep 24, 2024 4-16-38 PM.txt

The figures are in order of the measurement taken.

The lens actually was f=50mm and f=-50mm. I have changed the beam characteristics accordingly.

The lens change was mentioned in 3563

There is a scale on the table kept in backward direction, i.e increasing distance from laser is decreasing measurement on the scale. 

In reference to elog 3561 the beam was as attached in Fig 1. The beam characterization was originally done with f=100mm lens at 101.5cm. The waist of beam before the lens was at -47.1 mm, i.e at 101.5 cm +4.71 cm=106.21 cm

According to the elog the lens f = 100 mm was moved later by d=0.2m. But, now the setup has two f=50mm lens. This was never mentioned in elogs that the lens was changed. 

For the modified setup:

The two f = 50 mm, -50mm lens are placed at 96.5 cm and 90.5cm.Hence, the relative distance between lens and waist of beam is 9.71cm and 15.71cm respectively.

The new beam propagation is as in Fig 2. I propagated the original beam (one before f=100 mm lens) after the two f = 50mm lens. 

The beam power before filter is 64mW. 

I wish to replace the energy filter before the HWP on the EOM path, with a beam splitter or beam sampler and make a separate path for SLM. 

The Vpi, half wave voltage for the EOM is defined by the equation

V_{pi} = 0.361 * lambda - 23.844 = 0.361 * 1064 - 23.844 = 360.26 V (considering crystal with 14pF capacitane). The one we have says a capacitance of 12pF. 

(where lambda is in nm)

I tuned the circuit a bit more to obtain the gain of 7.397k with Moku supplying a 0.05V. So, with the updated circuit we will have

1. 0.05*7.397k = 369.8 V

2. Impedance of 48.9 ohm

3. OpAmp current of 11 mA.

4. Resonant frequency of 0.39MHz

I have updated the circuit diagram and transfer function.

PS: Moku can provide minimum of 1mVp-p using waveform generator function. 

Nishino

This is a continous work of 3744.

I replaced the mirror mount from LIOP-TEC's steering mirror to a rigid lens mount. Even with this new mount. there is still a peak structure around 600-700 Hz. This indicates that this resonance originates from piezo+mirror mainly, not from springs of the steering mirror

Fig. 1: OLTF and OLTF/Filter (=A*H*10) 

Fig. 2: Actuator efficiency in fourier domain

Fig. 3: Comparison with the LIOP-TEC mount.

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.