Cryolab Setup Diagrams and Lock Settings in multi-instrument mode

Attached are

1. The laser lock box settings via screenshot in multi-instrument mode using the PLL as the modulation setting.

2. Diagram of multi-instrument mode for reference.

3. Ariel photo of the set up.

4. Inkscape drawing of the set up.

Also should note when scanning the cavity using the current it should be safe to use the full range (2V). The TEC controller should be set to ~10.5kOhms, but double check the range on the integrator is roughly centered.

SNSPD Calibrations

Andrew Muller and I have completed our calibrations for the new SNSPD system which utilizes a Yokogawa frame controller. The results can be seen in the first attached image. On the left side of the table we list the numbers achieved on the older system and on the right the Yokogawa. These values include Dark Count (DC), Theoretical or computed number of expected photons/second, maximum and minimum achieved photon rate (as a percentage of theoretical rate), as well as the applied bias voltage on the SNSPD. The results for the dark count are varied between the two systems as the older unit had shielded fiber optic cables and the new system had not received this upgrade yet thus we saw an increase in dark counts by an order of magnitude. Both systems were given the same target rate of 100k photons/second and through calibrations made in python that are seen in the code "photonrate.py" and the newer "photonrate_yokogawa.py" a theoretical maximum photon rate (109k) was calculated based on the readouts on the power meter while cycling through each attenuator module to in order to account for differences or fiber loss. The code then automatically sets and attempts to achieve the desired rate. The efficiencies are then calculated by the resultant photon rate, with respect the the theorized rate, readout by the counter (seen as item 1 in the second image). Maximum and minimum values represent that of the highest and lowest achieved rates when adjusting the polarization of the optical fiber exiting from the laser which affects the rate readout on the counter (but not the power meter). Our results showed that the newer Yokogawa system was capable of achieving very similar and slightly higher efficiencies than the older unit which came in about roughly 72% and 71% respectively. The Thorlabs power meter is shown as item 2 in the second image, followed by the older attenuator and switch modules as item 3, and the new Yokogawa system, item 4. The Yokogawa frame controller has a number of compatible modules which include an in unit laser, power meter, switch and attenuators. The Yokogawa power meter seems to have a broad range of power input (larger than the Thorlabs meter) and more tests will be done to test its accuracy and limits. Code will be uploaded to git this Tuesday.

Notes from Meeting with Maty Lesovsky

I had an impromptu meeting/tour with Maty Lesovsky. The following are the notes I took

 

Good needle valves for bringing things up to pressure

All metal angle valves

Avoid rubber oring

 

10^-10 l mbar/s cm^2 is LIGO’s desorption

 

Have metal bake out site

 

All metal bake out valves

KJL has rubber o ring which sucks in contaminants

Varian is a good brand

VAT makes large ones

 

Use research grade N₂ if you want to backfil

Can hook up to needle valve

Clean air cheaper

 

They have an SRS RGA 200

Realistically only gets to 100 amu

Hanford uses 1000, but this SRS should be plenty

 

Have custom controllers for bake out

8 W/ft

Takes 110-220 V

PID controller from computer, can tell ramp time and other parameters

They have prints of the circuits

 

They have thermistors on the outside

Get surface temperature, not in air

Tac weld for surface temperature

Omega or McMaster

 

They also have insulation we can use

 

200°C is standard for small stainless

This is 150°C because it’s so large

They think they’ll keep the turbo on during the bake out

Biggest concern is machining oils

 

Fiberglass tape (from McMaster)

Goes up to 300°C

Great for holding thermocouples

Has gone through hundreds of bake outs over years, been fine

Avoid fiberglass insulation

 

Iwata Scroll Meister pumps, equivalent to the IDP-7

Tri scroll

Have mufflers to trap chemicals out of them

 

Smart to have a safety shutoff in case you lose power

Cut power to turbo

Choke turbo if it comes back on with pressure

 

Do a rate of rise test on partial volumes and the whole system

Good to test if something is degrading

 

Have a battery backup for a couple hours to run the turbo so the turbo breaks don’t wear out

 

For controllers, have Terranova Model 934 wide range which are good

MKS PDR 2000 also nice and easy

Invest in a case to display everything

 

They have a lab view program to monitor the pressure and the RGA

Pfeiffer Vacuum Calculator Initial Impressions of Pump Requirements

Using https://vacuum-calculator.pfeiffer-vacuum.com and the previous post's volume and surface area data, I have some inital impressions of our pump requirements for the 8 m long interferometer.

Other assumptions:

Desoprtion: 1e-9 mbar*l/(s*cm²)

Leak rate: 3e-9 mbar*l/s

1. Our final pressure limitation will be a function of desorption, not leak rate, because our surface area is so huge

2. The time to reach 6 Torr, where Pfeiffer starts the turbos, is given approximately by 1 hr * (4.3 m^3/h rougher pumping speed / pump roughing speed)

3.

A. 3 HiPace 80 DN 63 get to a pressure of 10^-7 Torr in 12 hours, 10^-8 Torr in a week

B. 1 HiPace 80 DN 63 gets to a pressure of 10^-7 Torr in 36 hours, 5*10^-8 Torr in a week

4. A 1 m, 6.45 mm tube between the roughers and the turbos doesn't greatly affect the pump down time or the final pressure

CMTF Mode Match to Optical Cavity

On Friday, Chris and I worked to mode match our laser to an optical cavity. At the end of the day, we placed our lenses in roughly the location suggested by a mode matching calculation, but the mode reflected off of the cavity appears much larger than the incident mode, so we believe we need to move the lenses further to improve mode matching. The attached file shows the calculated mode matching solution given a beam profile of the incident beam and the waist size and location of the reference cavity.

Pyrpl Package for Red Pitayas Installed on CMTF Laptop

I installed the pyrpl package on the CMTF laptop along with the correct versions of other packages it needs. To test this, I ran the command "from pyrpl import Pyrpl", which will throw an error unless the packages are downloaded correctly. Here are some notes about how to go about this process: 1) Make a new anaconda environment running on python version 3.7 and install some package such as matplotlib. I'll assume this environment is called "RedPitaya" Note: The version needs to be python 3.7, pyrpl will not work with the latest version of python without some serious debugging 2) Navigate to the folder anaconda3/envs/RedPitaya/lib/python3.7/site-packages/ Note: on a PC, the file path is anaconda3/envs/RedPitaya/lib/site-packages/ Note: You may need to force your computer to show hidden folders to find these file paths 3) Download the pyrpl package from https://github.com/lneuhaus/pyrpl/tree/master 4) Paste the folder "pyrpl" from the github repo in step (3) into the folder from step (2) 5) Install the following packages into the conda environment RedPitaya: pyqtgraph, pandas, quamash, the current version of PyYAML, scipy, paramiko, scp 6) Open a jupyter notebook and run "from pyrpl import Pyrpl" If this works, or only throws an error message, the computer should be ready to interface with a Red Pitaya using pyrpl. If there's an error message, some package likely needs to be downloaded or needs a different version. Fix that and try again.

Profile of Beam Headed to Indium Cavity

We took a profile of the beam after the faraday headed to the cavity. To compute the beam parameters, I fit parameters to a TEM00 mode instead of using the beamspotsize python package to calculate parameters since that package allows M^2 to float, and the beam waist is inside the Faraday and unaccessible. Taking the folding mirror after the faraday to be z = 0, the waist is located at z = -102.5mm +- 26.1mm and the waist spot size is w0 = 55.0um +- 5.1um. The attached figure shows the curve fit results.

CMTF Optical Cavity Properties

We're preparing to set up a Pound-Drever-Hall lock to lock a Mephisto laser to a stable, indium optical cavity. The cavity has mirrors labeled "Y1-1037-0-0.50cc" and "PR1-1064-99-IF-1037-UV" the Y1 mirror looks to be a high-reflector with a zero-degrees angle-of-incidence and a 0.5 meter radius of curvature. The PR1 mirror looks to be a flat mirror coated to be 99% reflective at 1064nm on a 1037-UV substrate. Based on these parameters, we expect the cavity to have a finesse of F = -2*Pi/ln(R1*R2) = 625 where R1 = 1.00 and R2 = 0.99. The spacing between the mirrors is approximately 255mm and the mirror radii of curvature are r1 = 500mm and r2 = infinity so the cavity stability factor is g = (1 - L/r1)*(1 - L/r2) = (1 - 255/500)*1 = 0.49 so the cavity has a large stability margin. (Cavities are stable as long as 0 < g < 1 and are unstable otherwise.)

Added Faraday to Beam Path in CMTF at Fermilab

We added a lens, lambda/4, lambda/2, and a faraday isolator to the beam path on the CMTF table after the EOM. The faraday has 58mW of incident power and 50mW of transmitted power after tuning up the polarization with the waveplates and the beam position relative to the faraday using the lens. Before, we had problems with the beam clipping on the sides of the faraday when we tried to add it to the setup. After these alignment steps, the beam coming out of the faraday looks clean and gaussian -- see the attached image file.

Added EOM to CMTF Table

We added an EOM phase modulator to the optics table in the CMTF at Fermilab. There's 63.3 mW of power incident on the EOM and 60.6 mW of transmitted power through the EOM.

Bowtie Cavity Length Calculation and Update

To get the round trip Gouy phase of the cavity to 1/3, the total round trip length should be 2.4 m.

 

Current mirror locations: (X,Y) =  (10.655 in, 1.1033 in)

Current total round trip length = 4*X+4*sqrt(X²+Y²) = 85.47 in = 2.17 m

Need 2.4 m, so need to add 0.23 m = 9 in

This means every mirror needs to go 9 in / 8 = 1.125 in back

8 comes from 4 mirrors and the round trip

 

New mirror locations: (X,Y) =  (11.779 in, 1.163 in)

New total round trip length = 4*X+4*sqrt(X²+Y²) = 94.46 in = 2.40 m

 

Thus, I plan on buying sixteen 1.125 in spacers for the every mirror.

Preparing to add Phase Modulator EOM to Beam Path

We're going to add a Newfocus 4064 phase modulator (EOM) to the beam path to allow us to set up a PDH lock. We plan to place the phase modulator at the waist position of the beam. The waist size is 100um and the EOM has a 2mm diameter so we should have plenty of clearance. The EOM has a maximum intensity of 20 W/mm^2, and our beam has 60mW of power with a 100um waist giving a peak intensity of 4 W/mm^2, safely below the EOM's damage threshold.

Initial Beam Profile of Laser 256 in FermiLab's CMTF

An initial beam profile measurement of laser 256 at Fermilab indicates that it has a waist of 658 +- 173 um located at the front of the laser, a divergence angle of 6.36 +- 0.98 mrad, and a M^2 value of 6.17 +- 1.88. Since the waist is at the front of the laser and the beam needs to be attenuated before measuring it, I couldn't get any data points within 1 Rayleigh range of the waist, so the measured M^2 value is likely far from the true value. I measured the beam with a Thorlabs DCC1545M CCD camera and used the laserbeamsize python package to measure D4sigma beam diameters and characterize the beam waist, divergence, and M^2. The attached image shows the measured data and calculated beam parameters.

8 m Interferometer Vacuum Calculation

Calculation for Pfeiffer Vacuum Calculator:

Central vessel:

Treating as a cylinder

11.9 inch radius

11 inch height

 

V = pi*r^2*h = 4900 in^3 = 0.080 m^3

SA = 2*pi*r*h + 2*pi*r^2 = 1,700 in^2 = 1.1 m^2

End cube:

Treating as a cube, even though the inside is more spherical

L = 10 in

 

V = L^3 = 1,000 in^3 = 0.016 m^3

SA = 6*L^2 = 600 in^2 = 0.39 m^2

 

Tubes:

4 inch radius

275 in height (two 10 ft tubes + 1 ft T = 6.4 m, round up to 7 m including gate valve, reducer, etc)

V = pi*r^2*h = 13,800 in^3 = 0.23 m^3

SA = 2*pi*r*h = 6,900 in^2 = 4.5 m^2

 

Total:

Vessel + 5 Cubes + 2.1 Tubes (power recylcer ~0.7m):

V = 0.643 m^3 = 643 L

SA = 12.5 m^2

 

Assumed desorption: 1e-8 mbar*l/(s*cm²)

Assumed leak rate: 3e-9 mbar*l/s

Can then figure out what pumps and how many to use using the calculator

Lasers at Fermilab

I am working with Hudson Loughlin. He is visiting from MIT. We powered on the Mephisto laser 255 (formerly the L IFO of the Holometer). At Injection current of 2.017 and crystal temperatur of 24.57, we read 1.514 W using the Thorlabs power meter.