Alex and Daniel

We checked a Noliac NAC2125-H08 for shorts and found none. We measured the capacitance to be 2.4641 uF. The expected capacitance is 2.4 uF. We also measured a resistance of 3.5082 kOhm. When we pressed on the piezo, we noticed a voltage. We flagged one of the wires for polairty. See attached photos. We also noticed that the nylon tipped set screws that hold the piezo in place provide a voltage.

I put one Newport Dielectric Mirror, Laser Line, 25.4 mm, λ/10, 1520-1580 nm (10D20DM.8) each in the crusher and piezo bowtie subassemblies. The piezo subassembly also has a Clean Room Viton Fluoroelastomer O-Rings, Chemical-Resistant, 1/16 Fractional Width, Dash Number 020, 1309N22, from McMaster. After compressing the piezo and the o-ring by threading in the SM1 ring, I backed off the screws that hold the piezo.

The subassemblies themselves are mounted to test. I set up a Michelson Interferometer to test the piezo. The piezo leads are connected to a BNC, with the positive lead in the center of the BNC and the negative lead to ground. A Thorlabs MDT693B - 3-Channel, Open-Loop Piezo Controller is also ready to be used. The output port of the Michelson is a 1550 nm photodiode.

The crusher is mounted on a bowtie cavity and the beam profiler is ready to be used there.

Right now, I am waititng on a Thorlabs order I placed today to get fiber outputs mounted into SM1 rings.

I have dissasembled the axetris - EMIRS50 AT06V BR25M thermal source such that the reflective can was desoldered. Next, to properly mount the thermal source into the previously described lens tube assembly (11334) the thermal source was soldered onto a brass washer using thermal paste and the PCB oven. The end results are shown bellow in attachments 1-3. The parts for the assembly will be here on monday to be machined and assembled.

The source was placed as closely to the center of the washer as possible, but a custom washer may need to be designed such that minimum alignment is needed when assembling the fiber coulped device. 

The SNSPD will undergo a PCR test and be placed in the fridge monday as well. 

While cleaning the Newport AJS254-0.5K-NL Adjustment Screw, I sonicated three Newport AJS254-0.5K-NL Adjustment Screws in isopropyl alcohol at 30°C for 20 minutes. When I came back, I discovered the tip had dissolved. I thought the tip was stainless steal like the body, but it might not be. I reached out to Newport for clarification. If the crusher does work (we at least one screw on hand), we will need 3 more replacements.

[Daniel Torrey]

One of the low power paths in the power distribution center (See "C:\Users\gques\Nextcloud\GQuEST\Layout_Mockups\B102_starting_setup_pwr_dist.svg" for updated layout) is aligned with 84% efficiency through the fiber. We have light available for readout filter cavity science.

[Daniel Torrey]

Profiled the output of the SHG, data for which can be found at Nextcloud/GQuEST/B102/SHG/SHG Beam Profile/ .See attached. Note the output for the SHG fiber has a collimator, very easy to change the beam profile.

Set current to 2.3 amps. This corresponds to 3.96 W out of the amplifier. The beam goes through a PBS, 50:50, 90:10, and PBS. The waveplates before the PBS can be optimized to give <1% loss in the S pol. Assuming minimal loss at the 50:50 and 90:10 this gives 1.75 W into the fiber. With 85% efficiency through the fiber my best guess is we have ~1.48W going into the SHG. The readout on the power meter shows 38 mW. This can be adjusted by the ratios in responsivities of the power meter at 775 and 830 so 38mW * 207.1/146.77 = 54 mW of 775 nm light. If we believe the covesion data sheet it predicts ~350 mW for similiar inputs. Could our SHG be that much more inefficient? Based on the power we ARE getting out of the SHG, according to the data sheet, you would think were feeding in approximately 500 mW, which I don't think is the case. Don't want to stick the power meter in there though.

2.3 A on the amplifier was the previously calculated acceptable operating point to not damage the faraday isolator at the amplifier output. I'm assuming 50 mW of 775 nm light is not sufficient for all of gquest, although I don't have a good sense for this number.

https://wiki.mccullerlab.com/Main/NoliacPiezoInfo

SHG and temperature controller turned on and we are seeing 775 nm light (probably). Couple of things:

1) The thorlabs power meter doesn't have a 775 nm light calibration, if we want to detect 775 we may want to find another power meter. The closest it has is 830 nm. 

2) SHG temp controller takes ~350 seconds to stablize to within .005 of a degree. Set it to 50.461 C for maximum 775 effeciency.

3)The SHG cavity it wildly inefficient at low input powers, it produces 38.5 uW of 775 with an input of 28 mW (.13% effeciency, also for the record 4 uW measured at 1550 as well). I ramped the current on the amplifier to 1A. This corresponds to an input power of 93 mW which yields an output of 150uW (.16% effeciency). The SHG has been assigned the serial number S2300012, see that link for specs and manual for this which has an efficiency curve as a function of input power. Similarly for the temperature controller S2300013.

We also need a more permanent way to mount it to a breadboard if anyone wants to 3D print something for it.

Since the pulse tube cannot be easily turned on and off, I added a few lines of code to determine how much power the heaters on the coldplate must emit at equilibirum to maintain a temperature of 123 K. For the Cryomech PT30RM, it is 11 W, while for the Sumitomo CH110, it is 19 W. There is a small risk that this value is an order of magnitude too low for the CH110 since it has a lot more cooling power at higher temperatures. I belive my modeling is correct, howerver. For the PT30RM, I belive 11 W is close to the actual value.

I think this implies we should have a high power heater near the coldhead's linkage to provide a rough constant temperature and a much smaller power heater on the beamsplitter mount to provide fine PID control.

See attached file

While considering vibrations of the coldhead and what to do if they're problematic for the interferometer, an idea occured to me to cool the conductive bar as a reservoir, turn off the cold head, and then the beam splitter will slowly cool down from 123 K to 122 K and then heat up to 124 K. In order to tune this temperature, we would need to in situ remove ~95% of the conductivity from the bar to the cold breadboard. This remaining conduction would have to be pretty accurate as well. I consider a 10 kg copper reservoir and the two "best" coldheads, the Sumitomo CH110 which has a lot of cooling power, and the Cryomech PT30RM which has a fair amount of cooling power but should have minimal vibrations. In summary, this is a vialbe option if we can do two challeneing things: change the conduction between the bar and the cold breadboard in situ and turn the coldhead on and off a few times per day.

In addition, I looked into two other tricks to help us: increasing the mass of the cold breadboard and thermally linking the cold breadboard and the inner shield to provide additional time. The former does help the duty cycle and increases the warmup time while the latter has a worse duty cycle with minimal benefit over just cooling more mass. 

Modeling data below:

Hot inner shield, 4 kg cold breadboard:

CH110:

6:09:57 to cool everything initially

Get 7:33:57 before the breadboard hits 124 K, takes 0:04:39 to reset breadboard, 34:58 to reset bar to within 1 K of equilibrium (duty cycle = 0.94)

PT30RM:

13:54:56 to cool everything initially

Get 6:08:26 before the breadboard hits 124 K, takes 0:10:43 to reset breadboard, 4:03:00 to reset bar to within 1 K of equilibrium (duty cycle = 0.6)

Hot inner shield, 20 kg cold breadboard:

CH110:

26:09:36 to cool everything initially

Get 15:42:36 before the breadboard hits 124 K, takes 0:24:30 to reset breadboard, 0:45:37 to reset bar to within 1 K of equilibrium (duty cycle = 0.95)

PT30RM:

44:28:12 to cool everything initially

Get 11:45:47 before the breadboard hits 124 K, takes 1:14:48 to reset breadboard, 4:56:26 to reset bar to within 1 K of equilibrium (duty cycle = 0.70)

Cold inner shield, 4 kg cold breadboard:

CH110:

23:49:17 to cool everything initially

Get 17:57:21 before the breadboard hits 124 K, takes 3:55:45 to reset the breadboard, 12:22:07 to reset the inner shield to within 1 K of equilibrium (duty cycle = 0.6)

PT30RM:

43:15:39 to cool everything initially

Get 16:09:28 before the breadboard hits 124 K, takes 9:00:23 to reset breadboard temp to 123 K, 15:02:13 to reset the inner shield to within 1 K of equilibrium (duty cycle = 0.5)

[Alex Torrey]

We did a quick test of the input couplers we have on hand. Initially couldn't get more than 1% through the fiber. Plopped a f=1m lens about a meter away from the input coupler and now get ~80%. Will com eup with a proper MM solution for this tomorrow. 

Boris and I have been working towards getting the SNSPD into the cryo chamber. There have been some hiccups as the chambers in Downs 123 have gone down recently, but we are looking toward taking an initial PCR curve next week (10/23/23) for the newly assembled SNSPD. See images 1-4 for the constructed SNSPD, wirebonded at JPL.

For the initial PCR curve on the SNSPD (to ensure it is working properly) we will  use the top seen in image 3, which will allow us to place a fiber directly above the SNSPD for testing. Next, once we are happy with the results, we will go ahead and replace the top with a dark box enclosure to test the SNSPD performance on dark counts while completelty enclosed in the cryo-chamber.

Finally, we will be testing the SNSPD's thermal response to radiation using a thermal source (axetris - EMIRS50 AT06V BR25M, attachment 7) and the setup seen in image 5. This setup will consist of the voltage controlled thermal source being placed approximately 1 mm away from the fiber tip allowing for complete exposure. The remaining fiber will be encapsulated in a brass tubing leading to the SNSPD. The setup utilizes thorlabs SM05 tubes and brass optic spacers to allow the thermal source to be held closely to the fiber. See image 6 for a real image of this thermal source.

We will be ordering these parts soon and assembling in the coming weeks. 

Torrey and Daniel

We analyzed the data that I took from crushing the mirror. The results are a little weird; crushing the mirror didn't move the horizontal waist location but did change its size. The horizontal waist location got moved forward which is the incorrect direction. I pushed on the mirror as hard as I could and didn't break it, so I think we should try a coated mirror. 

Files attached

[Torrey Daniel]

Began initial set up of the power distribution center. We have all the parts according to the diagram. Things are roughly aligned up until the first 50:50 BS. Will do alignment into input fiber couplers tomorrow. Torrey will attach photos and diagrams in a comment on this post.

We also put all of the laser initialization on one breadboard. This includes the seeder, polarization paddles, fiber PBS, and amplifier. The amplifier output is mounted on the power distribution center.