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ID Date Author Type Category Subject
93   Mon Feb 28 14:57:24 2011 warrenCryostatDrawingscavity support version 2

 Quote: I think that gold heat shield and the radiative heater should go in-between the cavity and this holder. Otherwise, there will be a thermal short between the cold plate and the cavity.

So Rana,

Not shown in the drawing are sets of nylon screws and G-10 washers that hold the three distinct thermal masses together without touching.

The three separate masses are 1) cold plate, 2) heater plate, 3) mounting frame, rails, and cavity.

So am I right that you want the surrounding box to attach to the heater plate instead of the mounting frame?  Sounds ok to me.

Also not shown is the weak thermal link (so set the thermal time constant between the heater plate and the cavity).  So we need to mount the cavity heater and thermometer to the frame ( assuming there is enough thermal conductivity through the knife edge).  Haven't figured out why we need a radiative heater too.

1625   Fri Jul 14 13:16:35 2017 vineethNotesDigital PLLLaser transfer function measurement

The input impedance of the ADC channels is 1MOhm and the output impedance of the DAC channels is 50 Ohm.

 Quote: what are the input/output impedances of the pitaya?

1067   Tue Apr 22 13:56:08 2014 steveDailyProgressLab Workgreen glass dumps

Green glass transmittance                    is a bit higher at 1550 nm (~few ppm)

Reflectivity was measured at 1064 nm

2890   Wed May 4 15:52:56 2022 shruti DailyProgressPSOMAloop TFs and noise spectra

After some troubleshooting I realized that I was mistakenly measuring the PDH signal coming from the not-in-use north laser PDH mixer+LPF electronics box, so I changed that to the right one.

Now the LB1005 error monitor and PDH error point show pretty much the same noise spectrum [Attachment 1]. Input 1 (pink)- PDH, Input 2 (blue)- LB mon, Input 3 (green)- Ctrl.

I re-measured the loop transfer functions and they are so much less noisy. Also seems to have a UGF of 170 kHz! [Attachments 2, 4]. Attachment 4 is the same as Attachment 2 and includes the UGF calculated from raw data and not just the simple fit. Something weird happened in the closed loop TF measured at the control point which did not effect the OLTF estimation. The y-scale is in dB for the magnitude.

The estimate of the unsuppressed noise is now much higher after accounting for the new transfer functions for the data from 03-May-22 measured at the LB mon point [Attachment 3]. Compare with earlier estimate.

Attachment 1: 1DFC2C2A-ABB4-41ED-9F2C-7A667BAA4B96.png
Attachment 2: LoopTFs.pdf
Attachment 3: CalibratedNoiseBudget.pdf
Attachment 4: LoopTFs.pdf
2538   Mon Jul 20 08:59:02 2020 shrutiUpdateLab WorkAt cryo lab

## Notice of lab entry:

After going over the checklist outlined in the previous elogs by Aaron, I completed everything relevant in the one labelled 'before', 'lab entry'.

Entry ~08:30, Will be here until ~17:30, with a break for lunch and a meeting (12:00-14:30)

Purpose: To give myself a lab tour, clean up the area around the workstation I'd be using, arrange and label tools, record part numbers of components for the PSOMA experiment

I also went in to the EE shop to get a solder station and related implements that I could find more than one of. I've placed this on the table to the south of the cryo Q experiment, after clearing up the space and placing the boxes below the table (see pictures).

Attachment 2: 332F07DE-A250-44A6-BA28-5A0DF65207E9.jpeg
2539   Tue Jul 21 14:03:33 2020 shrutiUpdateLab WorkAt cryo lab

Notice of lab entry: ~13:45. Expect to be here until around 17:00.

Liz dropped off PPE that was collected from the 40m (Thanks Liz!), this included two sets each of items as marked on the safety tab of PSOMA inventory doc. Also, see Attachment 1. I have removed one set of items and placed them on the tan cart that I use. Aaron's set is still in the box by the door; while I have worn gloves and tried not to touch those items, please assume that I have.

I think I have located the PD readout circuits requested by Gautam, which was in Johannes' setup. See Attachment 2,3,4; the DCC number of 2 checks out. I have placed them in a box in the area near the entrance marked by a red square. Other items labeled with '40m' are also in that box.

Attachment 1: 156CA9F4-5287-4222-9C45-5ACA006DFEDC.jpeg
Attachment 2: 64F84876-1D78-427F-B272-5584D0D7AC2C.jpeg
Attachment 3: B56E1C6B-C039-4E7E-85F1-AEFE8FA1BEAB.jpeg
2546   Thu Jul 30 09:13:14 2020 shrutiDailyProgressLab Workbeam profile prep

Notice of lab entry: I will be at the cryo lab today (30 Jul 20) 9am-5pm.

Purpose: Beam profile the Rio planex laser

- Turned on the laser that goes into the east cavity on. Turned on the Tenma supply, then the laser current driver  D1500207 labeled'E'. Saw a tiny, but bright, green spot on the detector card.

- Located razor blade and translation stage, for the beam profile measurement but not sure which power meter/ photodiode to use for 1550 nm. I plan to move the optics on the path of the east laser (to the east cavity) in order to do this measurement and later set up the initial ring cavity

- Aaron suggested I do another airflow measurement within the lab. Without the scrubber, there seems to be no measurable flow around either the Cryo-Q table or the cantilever table. I moved the scrubber into the lab near the workspace at the north side of the lab and let it run on medium speed. A few cm from the scrubber it the airflow rate is almost 5000 CFM, but it becomes <40 CFM even as close as the Cryo-Q table and again becomes negligible near the cantilever table.

- I set up the translation stage, moved relevant optics, but will continue to measurement later after I've researched and located a 1550 nm power meter

Two of the four overhead lights over the west (cantilever) table don't work anymore. Three other overhead lights are very dim/out.

2547   Fri Jul 31 08:51:00 2020 shrutiDailyProgressLab Workbeam profile prep

Notice of lab entry: I will be at the cryo lab today (31 Jul 20) 9 am - 2 pm.

Purpose: Look around for components [power meter charger, power connectors for PDs, flashlights, etc], laser operating manual; find out specifications of available mirrors, RF PDs

Also, there seems to be only one laser temperature controller in the lab. The west cavity laser TEC port is not hooked up to anything. For the time being this is okay since we'd be using only one laser.

2548   Mon Aug 3 13:10:46 2020 shrutiDailyProgressLab WorkInitial experiments and prep

Notice of lab entry: I will be at the cryo this (03 Aug 20) afternoon

### Lights fixed, safety, cleanliness:

- On entering the lab I noticed that the work with the light fixtures was completed. Unfortunately I could not avert it or get it all covered in time; I had assumed that I would be contacted beforehand but was not. But, by inspecting the table I do not think it looked any dustier than before. For any such activity in the future after we’ve cleaned the optics, I will remember to get it covered beforehand.

- The particle counter did not seem to be saving any data so I’m unsure what the effect of this activity was. The 1 micron particle count:
When I entered (1 pm): 80
(6 pm) : 70
This change might probably be entirely attributed to the air scrubber.

- When Aaron and I chatted with Calum today about COVID safety, Calum pointed out that turning on any HEPA filters in the lab would reduce the time between single-person occupancy to almost 0 for our room, as it would serve as an additional air scrubber. I tried locating a switch on the cryo cavity table for the HEPA fans but could not locate it today.

### Laser and beam profile related:

- After reading through bits of the laser operating manual and turning on the east cavity laser, I turned on the TEC (thermo-electric cooler) box [TED 200 C] with neither the TEC nor the servo on. I used this just to read off the resistance values of the sensor. With the current drive off it was 11.2 k-ohms [22 C].

- I waited until the sensor readings stabilized to changing at the level of a few ohms around 8.5 k-ohms [28 C] in a minute and began measuring the beam profile. (See Attachment 1 for setup)
I could not mount properly the only translation stage I found since the holes on it were smaller than 8-32, and moreover, I could not locate anything suitable that fits into the 1/4" holes on the table with this.

- Nonetheless, when I took some data and plotted it, it looked like an error function so I took more data. Will post plots later after fitting and analyzing. I may have to repeat this again.

- The sensor for the power measurement was S122C (Germanium) with a range of 700-1800 nm and 40 mW. After setting the power meter to 1550 nm, the measured power of the entire cross-section was ~2.3 mW.

- Also in the image in Attachment 1, the two optics (HWP and mirror) near the fiber-free space coupler, were previously in the path of the laser and now moved to either side of the beam. No other optics were moved from the previous set-up.

Attachment 1: IMG_633BBA57553C-1.jpeg
2549   Tue Aug 4 14:08:44 2020 shrutiDailyProgressLab WorkInitial experiments and prep: Beam profile

Notice of lab entry: I will be at the cryo lab for a few hours today (04 Aug 20) afternoon

Update:

## Beam profile results [razor-blade method]

At a few locations along the beam I measured the vertical and horizontal beam radii by measuring the power at different positions of blade edge across the beam. The power measured at the photo-diode was fitted with  $a + b \times {\rm erf}(\sqrt{2}(x-x_0)/w_z))$ where $w_z$ is the beam radius at the location along the beam and $x$ was either the horizontal or vertical position of the blade.

### Results:

The standard deviation as estimated from the fits are lower than $\pm$0.002 mm for all estimated radii.

But with the crude nature of the setup and not having the laser temperature stabilized (resulting in power drifts while taking readings), I guess that the error in each measurement is higher. The data in Attachment 3 also has recorded the resistance of the temperature sensor at different points while taking the data.

 Distance [in.] Horizontal radius [mm] Vertical radius [mm] 5 $\pm$ 0.1 0.120 0.121 6 $\pm$ 0.1 0.146 0.150 7 $\pm$ 0.1 0.175 0.173 8 $\pm$ 0.1 0.203 0.200 9 $\pm$ 0.1 0.231 0.229

- Attachment 1 has the updated setup with the clamped translation stage

- Attachment 2 shows the measured points with the error function fits. The offsets between the different curves along the x-axis are arbitrary.

- Attachment 3 shows a linear fit and an estimated divergence angle. I've assumed that all points I measured are outside the Rayleigh range, i.e., away the beam waist. The caption '5H' means that this set of data was taken 5 inches away from the output coupler (fibre-to-free space) moving the blade in the horizontal direction.

- Attachment 4 has all the data and jupyter notebook with analysis

- Attachment 5 shows the beam spot on the view card

Attachment 1: IMG_0268.jpg
Attachment 2: Erf.pdf
Attachment 3: Div.pdf
Attachment 4: beamprofdata.zip
Attachment 5: IMG_0258.jpg
2566   Wed Sep 2 16:19:57 2020 shrutiUpdateLab Worklab entry, information gathering

Notice of lab entry: 20 Sep 2020   evening

Fiber modulators on the table :

1. Intensity modulators (BW: up to 12 GHz) MXAN-LN-10

2. EOM phase modulators (BW: up to 150 MHz) MPX-LN-01

Dimensions of vacuum cans mentioned in attachments.

Attachment 1: 7BA40146-4F86-4819-8D6C-FFDC8F246E50.jpeg
Attachment 2: 129FE089-1E57-4E6D-9E77-F80F8E124CD1.jpeg
2576   Tue Oct 27 15:57:27 2020 shrutiDailyProgressLab Workpsoma locking

Today I modified the optical setup with the aim of obtaining the beat between the two diode lasers for phase-locking.

I added pick-off polarizing beamsplitters with HWPs in each path for now (to be able to adjust their power) and mixed them at a 50/50 non-polarizing beam-splitter to eventually reach a Newfocus 1811 low noise PD.

I will add pictures and more details later.

2577   Wed Oct 28 12:42:31 2020 shrutiDailyProgressLab Workpsoma locking

## Phase-locking the two lasers:

- Although when we talked about adjusting the MZ-phase, we decided that having the phase/path length control with fiber components might be better initially (Refer Attachment 2), for now I began doing everything in free-space.

- Attachment 1 shows the setup as it is now. Previously I'd placed polarizing beam splitters instead of 90/10 beam-splitters because I thought it would be easier to work with, but now changed my mind and decided to stick with what we planned.

### Next steps:

(Once the beat is obtained on the spectrum analyzer)

1. Adjust set-point temperatures to adjust beat frequency to the right frequency.
Since ideally we want the two frequencies to be identical, it might be a good idea to add an AOM to one of the paths so that the first order beam is mixed with the other laser and this beat be compared to a stable reference for phase-locking.
But, initially we plan to skip the AOM.
2. Adjust the PID parameters if needed

- Measure the laser frequency noise

29 Oct 20:

I've added Attachment 3 -- which is the current free space version and some PLL electronics.

- It does not show the Mach-Zehnder part as that will be added only later

- This setup is asymmetric but in a future version we will change that

Attachment 1: Setup2020Oct27.pdf
Attachment 2: psoma_PLL.pdf
Attachment 3: psoma_pll_freespace_intermediate.pdf
2579   Mon Nov 9 14:40:46 2020 shrutiMiscEquipment LoanStuff for N2 transfer

I've placed the following items outside the cryo lab:

1. Cryo liquid N2 dewar

2. Funnel

3. Tube

4. Two pairs of cryo gloves

Attachment 1: IMG_0334.pdf
2581   Wed Nov 18 08:24:02 2020 shrutiUpdatePSOMAtemp control and transverse beam profiles

D [in.]

West laser (X) [um]  West laser (Y) [um] East laser (X) [um] East laser (Y) [um]
2 327.2, 336.5 332.0, 340.9 327.1, 332.8 330.0, 335.2
3 358.2, 269.6 363.4, 374.7
4 420.4, 439.3 417.8, 439.8
5 511.7, 549.2 510.2, 549.9 527.6, 550.7 519.6, 540.4
6 642.8, 688.0 630.6, 674.9
7 766.4, 807.9 754.6, 801.4 778.0, 848.3 716.0, 782.7
8 891.1, 932.6 894.7, 942.1
9 974.3, 1023.1 943.9, 1000.6
10 1142.6, 1193.9 1152.7, 1203.5 1092.2, 1159.7 1040.6, 1103.4

This is the data using the Data Ray Beam'R2 profiler with the InGaAs window. Attachment 1 contains images of each of those profiles.

D: distance from fiber launcher in inches; The two values in each of the cells are [Clip 13.5%, 4 sigma] respectively, i.e., the method used to calculate the beam widths.

The previous measurement using a razor blade refers to 'sigma' which I believe explains why these values are 4 times larger.

These profiles were taken with temperature stabilized such that the powers were ~1 mW.

East laser set to 8.070 k Ohm, West laser set to 9.065 k Ohm. I don't understand why there is such a difference.

I had hooked up the ITC 502 combi controller to the west Rio laser and used only its temperature controller. (I believe both the thermistors that measure the diode temperatures are TH-20k Ohm.)

Both the PID controllers work satisfactorily: the TED 200 C with the east laser stabilizes to within few Ohms of the setpoint thermistor resistance within some seconds;

the ITC 502 stabilizes at a similar rate but at an offset of ~10 Ohms despite the integrator being set to maximum. I fiddled around with the P and I settings a little but realized that this configuration seemed optimal.

To measure these profiles at different distances I moved the fiber launcher head and then replaced it back to its original position, roughly.

Attachment 1: beamprofdata.zip
2582   Thu Nov 19 11:23:44 2020 shrutiUpdateLab Workpsoma locking

Attachment 1: An updated version of the diagram in elog 2577 where the path lengths to the beat beam-splitter are identical. The fiber launchers and some components have been moved around, but everything after PO1.1 along the beam has been retained as before.

Attachment 2: Retaining the same configuration to the beat BS, the cavity with Mach-Zehnder interferometer has been added. Also the path lengths to the MZ input BS along both laser beam paths have the same length. Except for the ring cavity, the Mach-Zehnder is also balanced.

Attachment 3: Updates pertaining to the current setup

• Work in progress to achieve the configuration in Attachment 1.
• I have switched the two PDs so the beat can be measured with the Newfocus 1611 (has a larger BW) and the noise measurement with the east laser can be done with the Newfocus 1811.
• I removed the 10/90 pick-off circled in green, so that would have to be added to the path to continue the noise measurement.

Attachment 1: PLL_FS_sym.pdf
Attachment 2: MZ_PLL_FS_sym.pdf
Attachment 3: NewBeat.pdf
2585   Tue Nov 24 10:16:04 2020 shrutiUpdateLab Workpsoma locking

- Found a suitable power cable M-M for the New Focus 0901 power supply on the east table (I did not realize yesterday that these were the same cables). Then I checked the voltage on the pins and they were fine.

- Using the New Focus 1611 (1 GHz PD) powered by the New Focus 0901 +-15 V / 0.3 A max. power supply, I tried finding the beat note. I looked at the RF output on a HP 8560 E spectrum analyzer and the DC output on an oscilloscope.

The DC output ranged from 500 mV to over 1 V as I scanned the temperature of one or both lasers.

- When the east laser temperature read roughly 8.34 kOhm and west was 9.04 kOhm I saw a pattern as in Attachment 2.

Changing the temperature slightly did cause the peaks to shift about, and further when I changed the polarization of the east laser using the HWP the height of the peaks varied. They also disappeared when either of the beams were blocked.

The estimated peak power in the taller peaks is ~0.1 µW from the plot.

- I also tried scanning the temperature of both lasers again to possibly find a single peak. No luck yet.

Today, I didn't check the alignment very carefully and I probably have to tune it further after the changes that Aaron and I made over the past few days.

The next step is to do the phase-locking.

Attachment 1: BeatSetup.pdf
Attachment 2: BeatOrNot.pdf
2620   Thu Jan 28 18:03:53 2021 shrutiDailyProgressPSOMAcavity locking

Since the south laser path had the EOM for phase modulation and the north laser path had the intensity modulator, I chose the south for locking to the triangular cavity.

The setup was roughly aligned, but I had to make a few changes:

- The optic labeled 'A' in Attachment 1 had a LH mount which made it nearly impossible to see the cavity reflection. I hunted for a RH mount for the same optic without success, while hunting I decided to switch this R>96% optic to a R~90%.

- The optic labeled 'B' seemed to be a polarizing beam splitter. I switched that to a circular shaped non-polarizing beam splitter.

- I also modified the Y translation knobs of both the fiber launches to make the beam height 4-inches

The image in attachment 1 is modified from elog 2609.

Rana entered the lab and saw that that one of the east table lasers were on and turned it off, after a few minutes I noticed that the south path did not have a beam. Since we did not realize that the south laser was in fact replaced with the beam from the east table, Rana replaced the butterfly mount with one from the cabinet; the cables for the TEC and diode current were also switched out. Once we realized that the south laser was not connected to the current setup, I reconnected it (south laser) replacing the blue fiber from the east table. Both lasers seemed to lase just fine after these changes (after much troubleshooting).

There is no thermal paste on the south laser butterfly mount (may be required later if the PID does not function optimally).

Attachment 1: Path.pdf
2623   Mon Feb 1 18:25:47 2021 shrutiDailyProgressPSOMAcavity locking

### Some Observations:

• Temperature of laser (in kOhms) North: 10.056, South: 10.097
• Power (in mW) North: 7.02, South: 7.26
• Beat frequency: ~20 MHz, -50 dBm
• After changing south laser temperature to 10.985 kOhms, the beat moved to 40 MHz, 4 dBm (!)

## Some information:

• Ring cavity made of :

Ma R~90%, Mb R>96%, Mc R>96% RoC 1m Coastline Optics CO-SAP-1000-250-1.0MP

Ma -> Mb -> Mc -> Ma

• Photo-diode: PDA20CS

• Got the beam in the triangular cavity to more or less align, i.e., overlap with itself as checked on one side of the triangle
• I hooked up the transmission PD in the transmission path of Mc
• At different temperature settings, blocking the incoming beam (Mb -> Mc) resulted in the power becoming minimum and blocking the beam (Mc -> Ma) resulted in some variable fraction of the the nominal power which I take to be a sign of interference (?)
• I moved around the temperature using the setpoint knob, but since the movement of the knob was nonlinear which along with a nonlinear change in power and frequency (with temperature) made it hard for me to figure out exactly what was happening in the limited time I spent on this so far

## Next steps:

• Going to explore the laser lock on the Moku:Lab for a while, after which I'll decide whether or not to continue with that or move to mixers + PDH servo box

2626   Wed Feb 3 10:56:54 2021 shrutiUpdatePSOMAcavity locking

I've temporarily removed the phase modulation EOM out of the path to get more power into the cavity.

I have also changed the temperature of the south laser to 7.278 kOhms.

2630   Thu Feb 4 16:19:35 2021 shrutiUpdatePSOMAcavity alignment

I turned on both the lasers and TECs, and cleared out all extra optics/components from around the experiment.

When I re-checked the cavity alignment I saw a large beam off the side of the main beam when the main beam was not blocked, both on the third side (Mc -> Ma). I tweaked around with the alignment quite a bit and even though the beams seemed to overlap along one side (Ma -> Mb). I could not really check the third side properly.

The transmission PD shows that it is receiving power from more than one round trip as checked by blocking the outgoing light from optic Mc, but I'm still not sure if there is interference.

I also measured the beam profiles at different points on the path (will add the data later). but in summary,  the beam seems more or less collimated everywhere with a beam diameter of 2.4 mm.

[Rana, Shruti]

The fiber launch PAF2A-18C seems to have an output waist of 3.49 mm. We are ordering fiber launches with smaller waists, but in the meantime it was previously adjusted to have minimum divergence. Today Rana adjusted the three tip-tilt/ focus knobs to get the smallest waist before the entering the cavity, but it turned out result in the huge divergence within the cavity, then it was re-adjusted to a larger beam with lesser divergence, close to what it was initially.

We also experimented with a lens, but then decided against installing one after seeing that it did not help very much.

The transmission PD reading may be noisy/ somewhat incorrect because of scattered visible light.

### QUESTION: Do we have filters for 1550 nm that blocks shorter wavelengths well?

2632   Tue Feb 9 11:14:48 2021 shrutiUpdatePSOMAcavity alignment

I removed some of Zach's optics and a large post from the south west corner of the table and placed the Vitek monitor.

I also placed a HWP and PBS in the transmission path to split the light between the transmission PD and the Vitek camera. Hunting for a suitable DC power supply for the camera.

2637   Wed Feb 10 09:52:45 2021 shrutiNoise HuntingLaser"North" current driver having slow current fluctuations

The .mat file was the only one I found on the Moku/iPad dated 4 Feb 21. I could open it on Matlab 2019 after re-downloading it from Box: it saved as a 1x1 struct with fields including a table for 'time' and another for 'data' which includes all the frequencies, phases, and amplitudes. The default storage is binary .li and I think Anchal has some python scripts to convert them.

2646   Tue Feb 16 11:30:14 2021 shrutiUpdatePSOMABeat recovered, fiber organization, alignment

I played around with the temperature and current to recover the beat (Attachment 3):

south laser temp: 9.373 kOhm, north laser temp: 9.602 kOhm

The low frequency oscillation still remains.

I decided to re-organize the fiber to make the north and south paths more evident visually. In the process, probably because I could not quite see the fiber coupler and was inserting it incorrectly or I somehow damaged the fiber coupler, the north coupler on the ADAFCB4 did not mode-match adequately so I replaced it with a single coupler borrowed from the west path in Johannes' setup. Now both paths at the output of the fiber show ~2 mW power and the beat is at around -15 dBm. (Attachment 1).

I've replaced the south path fiber to free-space coupler mount and post with an adjustable one to get the beam height to 4 inches. (Attachment 2)

Attachment 1: F2E33DA5-DB03-46EC-B341-E388D96F1BC5.jpeg
Attachment 3: Beat_low_freq_oscillations.mp4
2649   Wed Feb 17 11:56:20 2021 shrutiComputingPSOMACavity design

The code for this can be found here. I have also updated the PSOMA Wiki with similar information.

## Attachment 1

This is an updated diagram including the sidebands at around 33 MHz since that is what the available oscillator at the Cryo lab provides. The exact modulation frequency (within 1 MHz) does not seem to matter much since it only changes slightly the relative position, with the carrier, of the peaks created by the sidebands.

The numbers in the legend refer to m+n

$L_{rt}$ is the round trip length, $R_c$ =2m the radius of curvature of the only curved optic in the triangle cavity with the specifications of the one currently on hand, $\theta$ is the vertex angle at the curved optic (twice the angle of incidence).

The angle of incidence at the input coupler is $45^\circ$ because of its coating specifications.

Without any optimization the cavity scan can look like that in Attachment 2 (the sidebands are shown separately for a little clarity).

If anyone is interested in running FINESSE and other packages on Google Colab: this may help. [Access with Caltech credentials]

Attachment 1: Optimized_incl_sidebands_old_2m_33_5MHz.pdf
Attachment 2: Unoptimized.pdf
2658   Fri Feb 19 14:14:29 2021 shrutiNotesLaserPower vs. Temperature plots for Rio PLANEX
I turned on the temperature control and TEC for the North laser with the TED 200C laser controller to measure the power dependence on temperature.
The power was measured right after the fiber launch. Laser -> Faraday Isolator -> Intensity modulator -> 90% PO -> Fiber launch

The data and code for plotting is in Attachment 1.

The plot is in Attachment 2.
While the sensor resistance decreased (corresponding to an increase in the laser temperature) an abrupt decrease in power was seen at 8.72 $\pm$ 0.01 kOhms [close to 28 C];
When decreasing the temperature (measured by an increasing sensor resistance) an abrupt increase in measured power was seen at 10.23 $\pm$ 0.01 kOhms [close to 24 C].

The two sensor resistance values for abrupt power change was determined visually from the graph.

Attachment 1: PvsT_20210219.zip
Attachment 2: PvsT.pdf
2666   Thu Feb 25 22:34:48 2021 shrutiComputingPSOMACavity design

### Two possible good configurations.

Code for creating these are found on our GitHub repo

### Explaining the plot:

• xaxes: Frequency detuning of laser wrt cavity
• yaxis: Power transmitted through curved optic/ Incident power on cavity
• Non-black lines labeled in the legend refer to m+n and the same line contains contribution of both the carrier and the first order phase modulation side-bands.
• Dashed lines correspond to different (m,n) modes coloured so that all modes with same m+n have the same colour
• Black line is the total power in all modes for the carrier and sidebands
• Cavity finesse ~312 with input coupler transmission = 0.01
• The frequencies written near the central peak are the separation from TEM00 of the closest two peaks

Attachment 1: CavityDesignPossibility1.pdf
Attachment 2: CavityDesignPossibility2.pdf
2683   Mon Mar 15 12:11:51 2021 shrutiNotesLaserPower vs. Temperature plots for Rio PLANEX

## South Laser [Attachment 1]

The power dependence on temperature at different diode currents:

• The plots are linear in sensor resistance on the x-axis
• (Top figure) At 130 mA, while the sensor resistance decreased, an abrupt change was seen at 6.73 kOhms, and while increasing it was at 8.27 kOhms. At other regions it is locally reversible, i.e., going back and forth causes the same curve to be plotted.
• (Top figure) This trend is repeatable, as the black lines show the results of the same change performed a second time.
• (Middle figure) At around 120 mA, three such abrupt changes was seen in the range the data was taken.
• (Bottom figure) Similar plot at 100 mA.

Data and notebook for plotting in Attachment 3

## Conversion to Temperature

This notebook uses Rtyp values mentioned on the Rio Planex Datasheet found on the wiki documents page to obtain the plot and fit in Attachment 2.

That was used to make the temperature in deg C axes in Attachment 1.

Attachment 1: South.pdf
Attachment 2: RtoT.pdf
Attachment 3: SouthData.zip
2685   Thu Mar 18 10:08:40 2021 shrutiUpdatePSOMACavity design

Using the latest beam profiles in Attachments 3,4 and the design in Attachment 1, I calculated the mode-matching solutions found here. The one I decided to go with is in Attachment 2.

Attachment 1: CavityDesign_L40cm_R2m.pdf
Attachment 2: MM_L40cm_R2m_RA.pdf
Attachment 3: North_corrected.pdf
Attachment 4: Sourth_corrected.pdf
2686   Thu Mar 18 16:44:33 2021 shrutiDailyProgressPSOMAcavity alignment, RF oscillator power and frequency

Proceeded to align the cavity as outlined in elog 2685.

I also measured the output of OCXO using the Moku; all channels have 10dB attenuation and 50 Ohm impedance.

Attachment 1: 32.7 MHz; Channel 1 (red) is 'TO EOM', Channel 2 (blue) is 'TO LO'.

Attachment 2: 33.59 MHz; Channel 1 (red) is 'TO EOM', Channel 2 (blue) is 'TO LO'.

Attachment 3: Channel 1 (red) is 'TO LO' at 32.57 MHz, Channel 2 (blue) is 'TO LO' at 33.59 MHz.

The data files for all the spectra can be found here.

Attachment 1: MokuSpectrumAnalyzerData_20210318_162955_Screenshot.png
Attachment 2: MokuSpectrumAnalyzerData_20210318_162552_Screenshot.png
Attachment 3: MokuSpectrumAnalyzerData_20210318_162358_Screenshot.png
2693   Tue Mar 23 11:07:56 2021 shrutiDailyProgressLab Worklab temperature logging

Lab temperature is now stabilized. The particle counter is now logging the temperature, but not the AD590 which records X1:AUX-LAB_TEMP_F.

The AD590 history also seems different from the previous record.

Attachment 1: Screenshot_from_2021-03-23_11-06-46.png
Attachment 2: Screenshot_from_2021-03-23_11-04-15.png
2695   Thu Apr 8 22:47:03 2021 shrutiDailyProgressPSOMACavity locking and temperature scan

[Rana, Shruti]

Today Rana pointed out several improvements to the setup including fixing some finicky knob situations. The cavity and setup are now in a good state with monitor and PD connected, although we still have not seen resonance (Will be Attachment 2 soon).

According to the calculations in Attachment 1 a 1V change in the 'TEMP TUNE' input of the ITC-502 temperature (and laser current) controller would correspond to a change of 1 GHz in laser frequency at the current operating point (8 kOhms 'T_ACT' as displayed).

We send in a 1 Hz triangle wave with V_pp=1V into the TEMP TUNE input and make tiny changes to the alignment while monitoring the monitor for flashes and the DC reflected power for a steep drop.

RXA edit:

• We measured the input coupler transmission to be 2.5% for S-pol, so the cavity Finesse = 2*pi/(1 - T) ~ 250
• From the overhead picture, you can see that the cavity length is ~15-16 screw holes, so L_{RT} = 16" = 40 cm. So the FSR = c/0.4 ~ 1 GHz.
• So, assuming the cavity linewidth is then FSR/Finesse = 3 MHz, we want to make sure that our scan velocity is no faster than ~ 1 GHz/s, so that we are able to see the resonances easily on a 1 s oscope trace.
• The diamter of the beam transmitted through the curved mirror of the cavity is ~3 cm on the monitor.
• The mode-matching is still far off, since the beam after one round trip is much bigger than the input, but I estimate the mode matching is ~30-50%. Good enough for getting some flashes.
• It would be good to find a mount for the 1" optics that allows us to cleanly get the 4-ports without clipping.

## Other To Do

• Get a new power adapter for the camera (weird flashes occur when shaking it, confuses the alignment/locking process)
• Find/purchase a thread adapter to attach longpass filter to Watec camera
• Eventually organize and safely store all ND filters and other optics in the cabinet
Attachment 1: TemptuneCalc.pdf
Attachment 2: Untitled.png
2699   Wed Apr 14 17:15:23 2021 shrutiDailyProgressPSOMARoC measurement

### Attachment 1:

Result. Measured radius of curvature seems to be closest to 0.4 m convex.

### Attachment 2:

Beam profile bitmap images. Widths taken read from the image.

### Attachment 3:

Code used to plot Attachment 1.

Attachment 1: RoCis0_4mConvex.pdf
Attachment 2: 20210412.zip
Attachment 3: test_roc.m
%% beam fit

close all
clear classes
clear all

zScan = [3 6 9] * 0.0254 - 0.023 + 3.7e-3; % inches to m
xradiusN = [874 1021 1186] / 2 * 1e-6; % um
yradiusN = [838 1008 1178] / 2 * 1e-6; % um


... 197 more lines ...
2700   Thu Apr 15 16:28:20 2021 shrutiUpdatePSOMAsetup to do both locking and incoherent 3CH

Highlighted part of the setup shows what is required to continue with the cavity work. The 10% beam from the south laser and other available items should be sufficient for Aaron to continue with the incoherent 3CH stuff.

Attachment 1: table_setup.pdf
2701   Thu Apr 15 19:24:35 2021 shrutiDailyProgressPSOMARoC measurement

[Rana, Shruti]

### Attachment 1: Figure updated with beam profiles measured for the concave side of the optic. Consistent with RoC = 1 m concave.

• Turns out the optic was installed on the mount the with the side with HR coating for 1550 nm at the back. Verified by observing the color of reflected light from both sides: the concave side reflected green light while the convex side reflected red light. The side HR coated for 1550 nm must be AR coated for 1550/2 nm (close to visible red);  the concave side showed no red reflection and therefore is consistent with being HR coated for 1550 nm.
• The RoC measured for the convex side is not -1m because of the presence of additional material with a different refractive index in the path.
• The blue circles in the plot with x-values of 1 m and 0.85 m are not accurate because they were measured at large incidence angles on the curved optic. The remaining values were measured at small incidence angles. The results therefore seem consistent with a radius of curvature of 1m.

#### Attachment 3: Beam profile data

This refers to curved optic labeled SN 1.0-Si-1.0M; previous record of it found in elog 2562.

Attachment 1: RoC.pdf
Attachment 2: test_roc.m
%% beam fit

close all
clear classes
clear all

zScan = [3 6 9] * 0.0254 - 0.023 + 3.7e-3; % inches to m
xradiusN = [874 1021 1186] / 2 * 1e-6; % um
yradiusN = [838 1008 1178] / 2 * 1e-6; % um


... 197 more lines ...
Attachment 3: concave_beamprofs.zip
2703   Wed Apr 21 09:52:11 2021 shrutiUpdatePSOMACavity design

Latest cavity design (attachment 2) and mode-matching solution (attachment 1).

Attachment 3 suggests the tolerance of this setup and attachment 4 is an alternative mode-matching solution.

Attachment 1: Mode_match1.pdf
Attachment 2: RoC_1m_lrt_582mm.pdf
Attachment 3: Tolerance.pdf
Attachment 4: Mode_match2.pdf
2705   Thu Apr 22 10:43:25 2021 shrutiUpdatePSOMACavity aligned and resonant flashes observed

After aligning the cavity roughly to the solution and adding lenses according to the mode-matching solution found in elog 2703, I observed some higher order mode flashes on the camera and also saw dips in the reflected power (as in the first few seconds of Attachment 1). I adjusted the cavity yaw alignment since the higher orders were along the yaw-axis while Aaron tuned the temperature sweep and offset to see TEM00 flashes (as in the last few seconds of Attachment 1).

Mode matching efficiency ~ 73%, since the dips corresponded to 150 mV and the non-resonant region to 550 mV as seen on the oscilloscope.

Attachment 1: Flashes.mp4
2708   Thu Apr 22 20:25:49 2021 shrutiUpdatePSOMAsetup to do both locking and incoherent 3CH

 Quote: Highlighted part of the setup shows what is required to continue with the cavity work. The 10% beam from the south laser and other available items should be sufficient for Aaron to continue with the incoherent 3CH stuff.

Attachment 1: Setup20210426.pdf
2713   Tue Apr 27 19:37:49 2021 shrutiUpdatePSOMAPDH error signal

## Attachment 1: PDH error signal with monitor flashes

Using the setup shown in Attachment 3 (diagram here) (cavity design here), where the RF output of the free-space 1811 photodiode is sent to a Level 17 mixer ZFM-3H-S+ and then to a low pass filter SLP-1.9+ (cut-off at 1.9 MHz), I observed the PDH error signal on an oscilloscope while scanning the temperature.

Attachment 4 is a single-shot measurement of the error signal.

EOM: MPX-LN-0.1 driven with -5.8 dBm at 33.59 MHz using the OCXO pre-amp EOM output at 30 dBm attenuation.

LO: Driven at 33.59 MHz using the LO output of the OCXO pre-amp with no attenuation, estimated to be ~13.8 dBm.

The power levels of the OXCO outputs were the peak powers calculated by the Moku while observing the spectrum. The Moku itself produces a lot of distortion (many prominent harmonics were seen) while measuring this spectrum, these harmonics were less prominent when the scale was changed or when the input was attenuated sufficiently.

### Attachment 2:

Picture of beat note measurement between North and Teraxion requested by Rana.

Attachment 1: PDHerrorsig.mp4
Attachment 2: BeatNX20210427.pdf
Attachment 3: IMG_0215.jpg
Attachment 4: PDH.pdf
2731   Fri May 7 13:15:07 2021 shrutiUpdatePSOMACavity locking, feedback to laser

[Shruti, Rana]

I made that the ITC 502 current driver was in constant current mode where the feedback coeff is 20 mA / V $\pm$ 5% and bandwidth 500 kHz; with the laser coefficient being 100 MHz the net feedback coefficient would be 2 GHz/V.Then, I looked at the level of the PDH signal which was roughly $\pm$ 1V.

In order to attenuate the signal going in to the MOD IN of the ITC 502 current driver, Rana suggested using the 50 Ohm output of the SR560 with two series 20 dB attenuators and a BNC T with one port going to the MOD IN and the other port terminated with 50 Ohm.

With the SR 560 set with 1 Hz low pass and gain of 10, the cavity locked for 3-10 seconds when it came close to resonance as seen on the monitor.

The three attachments are the PDH signal (purple), cavity reflection (blue), and cavity transmission (yellow) when the cavity seemed to lock.

Attachment 1: IMG_0217.pdf
2732   Mon May 10 10:20:54 2021 shrutiUpdatePSOMACavity locking, feedback to laser

When I arrived today, the settings on the SR 560 were: Coupling: GND; Filter: 0.1 Hz Low Pass 6dB/oct roll-off; Gain: 100; Gain Mode: High Dynamic Reserve.

I tried to move around the temperature and gain to get it to lock, but it did not seem to do so at those settings. I finally managed to get it to lock indefinitely (at least 30 min) when I used the following settings:

Coupling: DC; Filter: 10 Hz Low Pass 6 dB/oct roll-off; Gain: 50; HDR.

Temp sensor resistance when locked was 8.447 kOhms.

The control signal is shown in Attachment 1 (while locked).

After ~30 min after Attachment 1 was taken, there seems to be a ~1 V offset accumulated on the control signal (as seen in Attachment 2) which should be 0.1 V after 20 dB attenuation and therefore be a change in current of 2 mA; this is consistent with what I read off from the available digits on the ITC 502 display.

Attachment 1: ControlSigLockedCav.pdf
Attachment 2: ControlSigCavLocked2.pdf
2751   Fri Jun 11 08:58:44 2021 shrutiDailyProgressPSOMASpurious peaks

Yesterday Rana pointed out the peaks at 350 kHz and its harmonics suggesting that the loop was oscillating. He also added a RG850 long pass filter 3mm thick to the transmission PD. Despite the specs mentioning that the transmission at 1550nm was over 99%, this signal seems to have decreased (yellow trace in Attachment 5).

I also adjusted the servo gain at the SR 560 and found that the loop could 'lock' even with a gain of 5. I was not able to lock with gain of 2. Previously, the gain was set to 50.

### Investigating the spurious peaks

Attachments 1 and 2 are the PDH signal measured after the SR560 from its 600 Ohm output.

In Attachment 1, the cavity is PDH locked using servo (SR560) gain of 5. The peak at ~350 kHz and its harmonics are visible. In Attachment 2, I tuned the temperature away from the locking point while the servo is still active and the peaks are still visible. The same oscillations are also seen in Attachment 5.

Attachment 3 and 4 are taken from the fast channels in the DAQ system. The gain at the SR560 was set to 50 for the reading in Attachment 3, and was set to 20 for the reading in Attachment 4. The gain setting of 50 seems to show better noise performance than 20 as seen on the digital system.

The purple trace and its persistence in Attachment 5 shows that the strength of this oscillating signal varies. This was measured with a gain setting of 5.

The oscillations were also seen when I locked the cavity with the LB1005 servo controller with gain=5 (lowest that allowed lock), PI-corner set to INT. Attachment 6 is the power spectrum of the output of the LB box when the cavity was locked.

Attachment 1: MokuSpectrumAnalyzerData_20210610_173153locked5_Screenshot.png
Attachment 2: MokuSpectrumAnalyzerData_20210610_173111unlocked5_Screenshot.png
Attachment 3: Locked_G50.pdf
Attachment 4: Locked_G20.pdf
Attachment 5: E6E3BD11-9678-466C-A2EE-FD848AB98E02.jpeg
Attachment 6: MokuSpectrumAnalyzerData_20210611_121141_Screenshot.png
2753   Tue Jun 15 14:59:29 2021 shrutiLab InfrastructureDrawingsnew lab layouts

Discussed the lab layout with Aaron today and combined some ideas from both attachments in the previous elog

Attachment 1: lab_layout_plan.pdf
2755   Wed Jun 16 10:29:58 2021 shrutiDailyProgressPSOMAInvestigating the peaks

Attachments 1 and 2 are the same plots in elog 2751 but overlaid. They are the noise spectra measured at the output of the servo.

### Attachment 1

Comparison between the LB1005 servo controller (yellow) and SR560 pre-amplifier(red) when the cavity is locked to the fundamental (TEM00) mode as seen on the monitor. Also shown in this plot (in blue) is the noise spectrum when the cavity is not locked to the fundamental, i.e., the temperature is detuned such that nothing was visible on the transmission camera monitor, but the SR560 servo is on.

### Attachment 2

Noise spectra measured with the SR560 as the servo, but with different gains. All were measured while the cavity was locked to the TEM00 mode as seen on the transmission monitor.

I picked up 4 packages from Downs (three from ThorLabs and one from MiniCircuits)

Attachment 1: SameGainASD.pdf
Attachment 2: DiffGainSR560.pdf
2756   Thu Jun 17 10:35:42 2021 shrutiDailyProgress Temp tune not absolute

The 'TEMP TUNE' input is relative after all with a coefficient of 0.2 kOhms/Volt. Max input voltage $\pm$10 V. (Attachment 1)

The 'TEMP OUT' is absolute (as expected) with a coefficent 2 kOhms/Volt.

Attachment 1: Temp_Tune.pdf
2759   Mon Jun 21 13:54:08 2021 shrutiDailyProgressPSOMAOpen Loop Transfer Functions

Having added the attenuator, A(s), at the input A of the LB1005 the loop algebra is changed slightly: Attachment 3 has the algebra and Attachment 4 helps with understanding the symbols. I have just considered this attenuator separately from the plant and servo.

### Attachment 1: Open Loop TFs

• The yellow curve is the actual open loop transfer function after subtracting 5dB in the magnitude of the ratio between the PDH error signal and the LB error signal to compensate for the 10dB attenuator at the input A of the LB box
• The blue and orange magnitude curves were recorded directly from the Moku
• The phase of the Math channel saved from the Moku seems to be a copy of the magnitude for all three OLTFs even though the screenshots seem to show a real phase (the data for this is saved in Attachment 3 and shown in the previous elog) so I re-calculated the phase but I'm not sure if it fully makes sense. (The calculation is in Attachment 4)

Attachment 2 is all the individual closed loop transfer functions that were recorded to calculate the open loop ones.

Attachment 3 has the data, settings, and screenshots recorded from the Moku to calculate OLTFs

Attachment 4 is the Jupyter notebook used to generate Attachments 1 and 2

Attachment 5 has the loop algebra and diagram

Attachment 6 is a diagram of the setup depicting the loop components

 Quote: $\frac{V_\mathrm{PDH}}{B}=\frac{PG}{1-PG}\frac{A-B}{B}$ $\frac{V_\mathrm{LB,error}}{B}=\frac{1}{1-PG}\frac{A-B}{B}$ $\frac{V_\mathrm{control}}{B}=\frac{G}{1-PG}\frac{A-B}{B}$ ... ... Indeed, we were able to eliminate the oscillations we had been seeing by adding a 10 dB attenuator between the PDH error signal and LB box input A, and changing the attenuator at the LB box output from 20 dB to 10 dB. [We also swapped out our ZFM-3H-S+ for ZFM-2H-S+, which has a 2 MHz low frequency cutoff compared to 50 kHz. Swapping mixers did not resolve the oscillation]   ... ...

Attachment 1: OLTF.pdf
Attachment 2: IndividualTFs.pdf
Attachment 3: OLTFs.zip
Attachment 4: LoopTFs.ipynb
{
"cells": [
{
"cell_type": "code",
"execution_count": null,
"outputs": [],
"source": [
"import numpy as np\n",
"import matplotlib as mpl, matplotlib.pyplot as plt\n",

... 203 more lines ...
Attachment 5: NewLoopAlg.pdf
Attachment 6: NewSetup.pdf
2762   Wed Jun 23 11:36:49 2021 shrutiElectronicsLab Workswapping mixer

I just switched the mixer back to level-17 and changed the low pass filter to SLP-5+ (5 MHz corner)

Attachment 1: MixerandLPFupdate.pdf
2764   Thu Jun 24 12:26:56 2021 shrutiDailyProgressControl Systemslow temperature control

I changed the error signal for the PID slow control to be the PDH control signal by modifying the file 'PIDConfig_SLDTemp.ini' in cryo_lab/scripts/temp_control on spirou.

The control signal does zero out when I actuate the loop, but the PID error signal shows strange oscillations when the control signal cable is plugged into the breakout board.

2766   Mon Jun 28 10:12:28 2021 shrutiDailyProgressControl Systemglitches, transfer function

The glitches seem to come from the slow controls output and temporarily result in an actuation voltage of +-10 V even when the limit for that channel was set to +-2 V in the PID script. This triggers the 'WIN' light and a beep from the ITC 502 while also losing the lock.

Aaron and I also had observed this last week.

[shruti, chris]

We were able to measure the loop transfer functions with the latest settings of KI=0.5 and PDH_CTL offset=2000cts on the slow control without being affected by the glitches too much. Chris also set up all the slow control channels so that they can be viewed with ndscope. In this we could also see that the transmission monitor sometimes glitched but the loop remained locked.

### Attachment 2:

Updated measurement similar to elog 2759

Attachment 1: glitches.png
Attachment 2: OLTF.pdf
Attachment 3: Setup.pdf
Attachment 4: Data.zip
2774   Fri Jul 2 11:29:52 2021 shrutiDailyProgressNoise BudgetCalibrating PSOMA noise budget

### Some observations

• When I entered the lab the cavity was already locked with a very bright spot. The transmission was over 1000 counts, and I was previously seeing 600, which was after Aaron improved the mode-matching yesterday.
• (Attachment 1)  It seems like the cavity was locked for almost 6 hrs with the temperature loop enabled before I entered.

• After tweaking around with the gain to improve the UGF of the loop, I set the gain to 5.5 from 4.7. Further details in next section.
• I changed the gain on the PDA20CS transmission PD to be 40 dB, it was previously 70 dB. I also adjusted the waveplate in the curved optic transmission to send more light to the PD and less to the camera. Many camera pixels were saturated. So now the X1:OMA-ERC_MON_RATIO is around 4 when it was previously around 8, and the transmission X1:OMA-ERC_TRANS_MON_OUT16 is at 400 counts, previously at 1000.
• I changed the KI value for the loop from 0.5 to 0.2 because I thought that there were very slow oscillations, but I don't think I noticed anything change when I did that, but I left it at 0.2.

### Maximizing the UGF:

• As I increased the gain on the LB1005, at around 5.5 I began to see a prominent broad peak at around 120 kHz in the noise spectra of the PDH error signal (Attachment 2). At roughly 5.7, I began seeing some saturation indicated by the presence of higher harmonics, which increased when I increased the gain further (Attachments 3 and 4).
• (Attachment 3) This made it possible to achieve a max UGF of ~120 kHz with other settings remaining the same.
• The offset from 0 dB to +3.16 dB   [8Jul21 edit: It should be 5 dB (voltage attenuated bt 3.16) since the attenuator was 10dB] is because of the presence of an attenuator at the input of the LB box, when measuring  PDH error signal/ LB error signal
• Technically the units on the axis is dB and not dBm for the yellow trace, which is PDH error/ LB error similar to the measurements described earlier.
• Not sure where the saturation (harmonics) is coming from.

### Noise spectra

• With the settings described here (from earlier), the uncalibrated noise spectrum is what is shown in Attachment 6. The data below and above 1 MHz were measured separately with different res BWs.
• (Attachment 7) With the settings at present, I took several noise spectra measurements with different frequency ranges and res BWs and overlayed them.

I saved all the data from the Moku I measured today in the mokuliquidwb Google Drive.

Attachment 1: Screenshot_from_2021-07-02_11-32-06.png
Attachment 2: MokuSpectrumAnalyzerData_20210702_141330_5p5_Screenshot.png
Attachment 3: MokuSpectrumAnalyzerData_20210702_141402_5p7_Screenshot.png
Attachment 4: MokuSpectrumAnalyzerData_20210702_141416_5p8_Screenshot.png
Attachment 5: MokuFrequencyResponseAnalyzerData_20210702_141630_PG_Screenshot.png
Attachment 6: Spectra20210622.pdf
Attachment 7: Spectra20210702.pdf
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