Crusher Data Analysis

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

Setting up the High Power Distribution Center

[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.

Second Table Unwrapped and Ready

The second table in B102 (the swing space) has been unwrapped and the HEPA filter has been turned on. The parts that were stored there should be recleaned because the table was really dirty and without the HEPA filter it looked like dust was accumulating on them. I am planning to use that table to prototype the LFC and to make the sled that holds the input/output optics so that it can be easily moved to the main space.

APD Circuit Update

My current design documents for the avalanche photodiode (APD) circuit board are shown bellow in the attachments. The current design for the Excilitas C30645 consists of using 3 power sources: a high voltage 85+ Voltage source (for bias voltage), and a +-30-40V source. These voltages will then be regulated down to 75V (TPS7A4001), and +-15V (LM317/LM337) respectively.

To create a low noise reference, the LT1021-5 precision 5V reference will be used in conjunction with an npn and pnp transistor circuit to create +-5V references. The +5V reference will be used as the input reference with an op455 op amp (capable of handling high voltages) to achieve an adjustable output bias voltage of 70, 65, 60, or 55 volts. The regulated 75 volts and -5V reference will then be placed on the op455's power terminals. Next, this output bias voltage will be sent through a buffer and accross the APD. 

Finally, the low noise transimpedance amplifier (op184) will take the signals from the APD and boost it to the DC and differential outputs. The current APD circuits are ready for testing in a lab as simulations have been done to confirm their viability. The last steps will be to chose a proper capacitor for the transimpedance amplifier such that it is properly stabilized. (A second post explaining that process will be added once done)

 

Amplifier Beam Profile

[Torrey]

Took a profile of the beam coming out of the amplifier. Attached is a plot with data and a fit. As you can see it is well collimated. The approximate radius coming directly out of the amplifier ~1micron. The damage threshold of the FI is 250W/cm^2. The peak intensity of a guassian 5 W beam out of the amplifier is then ~5 W / (pi * .1cm^2) *2 = 318 W/cm^2. I'd therefore suggest opperating at around 1.5A pump current to achieve ~2.4 W output at least to start. Alternatively we could have the FI farther away from the amplifier output.

Windows For the LFC

[Ian, Daniel]

We met to discuss the window design for the LFC with a cavity length of 4.49 meters. We looked at windows and single and multi port conflats and decided that the best option was to use the four port CF0600X4 (diagram of the conflat here). This would allow us to access inputs and outputs for each mirror if needed. I don't think we have any plans to use 775 nm to control the cavity but having the extra ports would allow for that and allow for different orientations for cavity. for example if we decide we want to have it enter and exit at a different port in the future. 

With the preferred conflat and window I did the calculation for where to put the mirrors. In window geometry notebook I calculate how far apart the mirrors need to be and the angle between the incoming and reflected beam. 

If we want all of the cavities inputs and outputs to be available then the angle of the incoming and reflected beam should be 3.7 degrees. This uses the middle 25% of the window so there shouldn't be any distortion. This gives a mirror separation of 2.2 inches from center to center. This is rather close but should be useable. These calculations also offer some wiggle room for moving the mirrors slightly apart. With this geometry the beam angle of 3.7 degrees means that the beams will be separated by about 1.2 inches one foot behind the cavity mirror (M1). This means the beams can be separated without too much trouble. I will update the layout for the LFC area also.

The windows for the chamber should be 2.75 inch windows with an AR coating for 1550. The VPZL-275LDIO2 which is the right size and optimized with the correct AR coating. If we wanted to use a 775 nm control we would use  the VPZL-275LDIO3 which is optimized for 808 nm.

We also came up with the mounts: we should get 1 Polaris-K1S3P which has piezoelectric control and 3 Polaris-K1S5 for the other mirrors.

Laser Amplifier Characterization

[Sander, Torrey]

First operation of the amplifier with the pump current running. First, there seems to be some slight discrepancies between the manual (https://mccullerlab.com/logs/lab/index.php?callRep=11279) and actual operation. The manual instructs:

1. Turn on seed light.
2. Turn amplifier key, after 30 seconds the enable/disable button stops flashing and there is ~300mW of light.
3. Adjust laser current, press enter, then click enable.

In reality it goes like:

1. Turn on seed light.
2. Turn amplifier key (the enable/disable button flashes indefinitely, says it is supposed to be 30 seconds).
3. Press the enable button (Only now is there light, manual suggests there should be light before this).
4. Use knob to highlight "current", press enter, change current with knob and press enter to apply amplification.

Only mention this because the manual explicity says, "To enable the power amplifier emission, press “Enable/Disable” on the front panel", which is not the case. On to the characterization.

 

We first calibrate how much power is being reflected by the BS to infer how much power is coming out of the amplifier. This is 1.45%. We then vary the amplifier pump current and measure the power reflected off the BS. Data in attached plot. It seems our maximum power out of the amplifier is just under 14W. Additional we look at the beam shape at each pump current. An example is attached as well as all of the profiles taken. Big take away here is the beam shape does not seem to vary with pump current.

 

Also as an aside we varied the input power to the amplifier, and as Lee suggested, the amplifier input saturates as any amount of input power did not change the output power (for input power >14 mW).

First operation of high-power laser amplifier

We turned on the high-power laser amplifier (NKT photonics Koheras Boostik) for the first time today, producing a high-power beam (did not measure the power yet, amplifier specs says it should be ~1.5W).

The input beam for the amplifier is supplied by the seed laser (Thorlabs ULN15TK), which produces ~50 mW of optical power. To attenuate this power to below the amplifiers max input power spec, the amplifier input power is controlled through a paddle polarisation controller and a polarising beamsplitter (PBS). One of the output ports of the PBS is connected to the input of the amplifier, the beam from the unused PBS output port can be used a monitor or dumped (see attached photo). Touching the non-polarisation maintaining fibres (yellow) upstream of the PBS results in power fluctuations of the seed beam and should be avoided (though they are clamped down so the effect of accidental touches is minimal).

The output of the amplifier is directed through the corner of a beamsplitter cube to create a low power beam from the reflection of the front surface AR coating. The high-power transmitted beam is dumped. The low power beam will be used to characterise the amplifier output.

Laser Table Required Components

Laser Table requirements and purchasing (might have some on hand)

Requirements

Power Distribution:

• 2 ft x 2 ft breadboard
• High power faraday isolator
• 5 Half waveplates
• 5 wave plate mounts
• High power PBS
• 4 PBSs
• 1 90:10 Beam splitters
• 1 10:90 Beam splitters
• 50:50 Beamsplittter
• 7 cube beamsplitter mounts
• Lens set
• 3.5 W beam dump
• 8 mirror mounts
• 8 mirrors
• Camera/Power Meter

• 5 fiber couplers
• 5 single mode fibers

 

SHG Sled:

• 2 ft x 4 ft breadboard

780 nm parts

Faraday Isolator

20 mirrors

20 mirror mounts

1 EOM

A lot of lenses

3 50:50 Beam Splitters

4 PBSs

4 AOMs

4 Quarter Waveplates

2 half waveplates

6 wave plate mounts

7 beam dumps

5 fiber couplers

5 single mode fibers

 

Single Bowtie:

• 2 ft x 4 ft breadboard

Half Wave plate?

1 wave plate mounts

1 PBS

9 mirror mounts

9 mirrors

5 power meters

1 camera

Lenses

2 EOMs

2 polarizers

2 fiber couplers

3 ~90:10 beamsplitters

 

 

Purchasing

• Baselab Tools

2 2x2 $498 each

4 2x4 $979 each

$4,912 total

 

Liop-Tec

Get equal mix of handedness, get high performance, get some with 3 screws, get equal mix left and right handed

20 SR100-100R-2, variety of colors

20 SR100-100L-2, variety of colors

60 or 80 Euro Each

2400 or 3200 Euro

 

64 total

32 R

32 L

 

Waveplates:

Lambda

Zero order optically contacted

6 Half needed

4 quarter needed

 

Beamsplitters from Thorlabs

3 BS015 (50:50), $245.74 each

3 BS027 (10:90 R:T), $245.74 each

6 PBS254, $253.89 each

 

Faraday Isolator

Thorlabs IO-5-15550-HP, @ 5 W, the waist needs to be 2.4 mm or larger

40 dB isolation

Max beam diameter 4.7 m

Gouy Phase of the Laser Filter Cavity

Our desired accumulated Gouy phase shift for a full round trip of the LFC is 120 degrees. I used this target to find the length of the LFC using the code in the Laser Filter Cavity Repo. To run the code run the test in T_Gouy_phase.py. Also included in this code is the finesse3 calculation for the LFC. 

The first plot "zero2seven_gouy_phase.pdf" shows the accumulated Gouy phase for different cavities of different lengths. They all have the same ROC on the M3 optic of 3 m. all other mirrors are flat. 

The second plot shows the Gouy phase accumulated for the desired cavity as well as its beam profile.

Amplifier Start Up

[Ian, Sander, Daniel, Torrey]

Using a face of a beamsplitter as power control out of the amplifier reflects .6% of the light. This should suffice. We have a set up ready. 

One problem we found is bumping the fibers in anyway varied the amount of power by alot. We don't want the input to the amplifier to change by an order of magnitude all of a sudden, so Daniel is going to 3D print a holder for the fiber polarization controller (paddle device). Alex is going to 3D print a holder for the fiber PBS as our current design doesn't quite work. After we get those two items we will attempt this again.

3D Printed a Cover for the ULN15TK Seeder Laser

Torrey and Daniel October 3, 2023

Daniel 3D printed a cover for the ULN15TK Seeder Laser that makes it very difficult to accidentally turn on or off the seeder. Torrey printed and attached warning labels conveying that one should not turn the seeder off so that the amplifier isn't damaged. If we are really paranoid, Daniel could 3D print a cover with a tighter fit.

Attenuating the laser with a mirror as a function of angle of incidence

Torrey and Daniel 10/3/2023

We measured the laser power coming out of the seeder to see if a Newport 10D20DM.8 could serve as a filter to image the light coming out of the amplifier. We measured the power incident, transmitted, and reflected for a few angles of incidence.

Data:

~<5 degree AOI:

Incident: 26.1 mW

Transmitted: 4.25 uW (0.00016 of the incident power is transmitted)

Reflected: 26.04 mW (0.9977 of the incident power is reflected)

Implied Absorption: 0.06 mW (0.0023 of the power is absorbed)

 

45 degree AOI:

Incident: 26.06 mW

Transmitted: 10.99 uW (0.00042 of the incident power is transmitted)

Reflected: 26.09 mW (more power is seemingly reflected than incident; some small measurment error)

Implied Absorption: 0 mW (none of the power is absorbed)

 

The conclusion is that the mirror's OD is between 3.4 and 3.8 depending on the AOI. This should work very well with a amplifier of 5 W, giving around 2 mW of transmission with little absorption and an easy to block reflected beam.

One complication is the back of the Newport 10D20DM.8 is frosted, potentially making the beam hard to profile.

SNSPD Uncertainty Update

After having assembled the dark box for the SNSPD, Boris has taken the SNSPD to JPL to wire bond the physical sensor to the newly assembled PCB and box. I worked with Jamie to learn how to solder the pins and SMA connectors to the PCB, and finalize the dark box by filling the pin holes with black epoxy. I will post updated images of the final outcome this week.

As for uncertainty measurements for the Yokogawa system (here-11226) I have begun writing automated scripts for running specific measurements outlined in the paper (attachment 2) which detail how to calculate and measure the uncertainty of the Yokogawa system. Thus far I have attained one of the primary plots for the calibration factor for the power meter based on wavelength (see attachment 1). 

Next I will need to check that the powermeter script auto-calibrates the power meter to the correct wavelength before each measurement and will repost more in-depth results. After, I will make a long accurate measuement of the callibration factor plot and save the data to be integrated (and updated when needed) in the script such that any measurment made on the system will take callibration factors from this dataset and integrate them into the overall uncertainty calculation (as seen in the paper attached). 

I will then be running a script to do the same process for changes in laser output power. Lastly, the uncertainties for the attenuators and optical switches will be calibrated accordingly with the previous measurements included respectively. The final script will allow a user to make a PCR curve and based on the set conditions (attenuation value, optical switches in use, and laser output power) will calculate the uncertainty of each measurement accordingly. 

 

Aligned Laser into Bowtie Cavity

I screwed down the sled with the laser to the breadboard and aligned the laser into the bowtie cavity. The laser is centered through the input port, onto the crusher, and out of the 3rd port. The beam was diverging, so I then added a 1 m focal length lens before the final steering mirror. This lens did not affect the allignment of the beam. The beam is roughly 2 mm while hitting the crusher mirror and has a smaller, unmeasured waist after leaving the bowtie cavity. I plan on making some measurments next.

Testing the Mirror

[Sander, Daniel, Torrey]

As discussed in group meeting, we tested the "mirror crusher" (the device that applies a force on a mirror in the filter cavities in order to change the radius of curvature of the optic, for wavefront control) yesterday. We first measured the beam profile and fit the data to the equation,

\[w^2(z) = w_0^2 + M^4 \left( (\frac{\lambda}{\pi w_0} \right)^2 (z-z_0)^2 \] ,

to get an approximate beam waist and location to use in the next step. The result for which can be found here.The optical layout of the system can be found here. We then wrote a quick code in Finesse to simulate the system, one for with a flat mirror, and then one for a curved mirror. The results for these can be found in the images attached labelled flat and curved respectfully. In the tables, the number of interest is under the w column, at the point n1.p1.i. This just corresponds to an arbitary point in space (where the scanning slit was placed). The difference of these values, and the estimated change in beam size from the crusher is then 38.1 microns. The actual measured change was (x,y): (17, 110). This discrepancy could come from the beam not being centered on the mirror being pushed on. Note that the model doesn't exactly agree with some of the experimental data in otherways, i.e. the expected beam diameter at the measurement point from the model is roughly 2 mm, where as the measured was ~2.7mm. I will update this post as the model is improved.

Additional improvements/iterations to be made:

-Maximize beamsize on optic thats being pushed on. Locate the waist some distance away. Then push on the mirror and see how the waist location changes.

-Improve collimation out of fiber. It is not collimated in the slightest, see here. We recently purchased a collimator that you can adjust along the z-axis to improve this. Will swap it out.

Layouts checkpoint

Here are the current layouts of the B102 space and a highly cleaned version of the renovation plans. These are for thinking through large-scale configurations. Let's keep live versions in https://wiki.mccullerlab.com/Main/Layouts and in the dropbox in GQuEST/Layout_Mockups (for now).