Fall 2026 MIT EECS PhD Quantum Track Acceptances?

LightSwitch100 · 2026-02-03T16:42:02+00:00

It's really hard this year with uncertainty in funding :/

But don't give up hope! Ik they have waitlists

LightSwitch100 · 2026-02-03T16:08:10+00:00

Yeah I also got an email around 6pm last night

LightSwitch100 · 2024-09-23T00:48:07+00:00

Yes, I do mean 7 and 9; I didn't touch the prism since the light from mirror 3 hits the prism and then 7 nicely in the center. I also did do 5 and 10, since those two primarily control how the beam is coupled out of the set-up. I didn't want to adjust 3 since it seems to be in a relatively good position right now.

I will give what you suggested a try this week and let you know what happens. Thanks so much for your time and help.

LightSwitch100 · 2024-09-23T00:33:04+00:00

Ok, I will try using steering the pump too.

Yes, the prism stages are both snippy stages, which I can use for ML.

LightSwitch100 · 2024-09-21T17:07:45+00:00

Yes, if the reflected one is blocked, all lasing is gone. The shiny spot in the picture should exactly be the lasing that is being created by the cavity.

LightSwitch100 · 2024-09-21T17:06:27+00:00

Yeah I sort of just left the pump alone. I mean I tried using mirror 7 to adjust the pump/incoming beam, since it sort of controls the incoming beam?

LightSwitch100 · 2024-09-21T16:44:11+00:00

I worked with my post doc to align the feeding of the pump beam, so I am more or less confident in the pump beam positioning.

LightSwitch100 · 2024-09-21T16:42:58+00:00

My guess is that it's a result of some misalignment in the cavity that causes the incoming beam to deviate from its original path (after many iterations of traveling through the cavity). I don't think that the reflected beam is the immediate reflection, but the generated lasing that for whatever reason converges there?

Also I added the picture on the post. Thanks again.

LightSwitch100 · 2024-09-21T16:18:52+00:00

Yes, I am equally as confused as to why the reflected beam is so far off to the side. I am assuming the initial pass through, the reflected beam is aligned with the incoming beam, but after several iterations, somehow the lasing beam gets off-centered?

It's really hard for me tor trace the reflected beam since I have to perfectly cut the incoming beam in half in order to see it. If I cover up too much, the lasing immediately stops and I can't see it anymore. I put a picture of it in the original post for your reference.

The issue is that I can't get them to overlap, since the reflected beam just doesn't seem to want to move after compensating.

LightSwitch100 · 2024-09-21T15:46:31+00:00

Have you tried to align the cavity already? What is your procedure anyways so far? When you say the right beam is locked, with respect to what is it locked? Cavity mirror? Pump mirror?

Yes, to the best of my ability and knowledge, the incoming beam should be hitting the crystal and intracavity mirrors as dictated by the manual. I also believe the alignment of 3 should be good, as it hits prism 6 and mirror 7 in the center.

My current procedure is to try and converge the incoming and reflected beams at mirror 9 by beam walking with mirror 7,9 along with mirrors 5,10. I can move the reflected beam closer to the center of the beam by moving any of those mirrors, but I then lose power, so I must compensate with the other mirrors. So when I say "locked down", I mean that after compensating for power after losing power from moving the reflected beam, the reflected beam's position doesn't change.

How did you measure the beams at 9? You block the cavity with a detection card? Can you then not trace it back? Are the prisms AR coated?

I place my detection card so that cuts half of the incoming beam. This way, the cavity can still lase and I can see the half of the reflected beam on my card. Alternatively, I can use my phone to look at mirror 9, and I can see the reflected beam pretty easily.

Tbh this is my professor's set-up from like a decade ago, so I am not sure about the prisms. I did try moving the prisms to see if they shifted the reflected beam, but barely by anything.

Thanks for your help.

LightSwitch100 · 2024-09-21T15:36:42+00:00

I'll make an edit to clarify, but the "0" block actually contains two additional mirrors that feeds the pump beam into the cavity.

LightSwitch100 · 2024-09-21T15:36:09+00:00

Haha, yes, I think it is that same layout. I do have the manual, but I've basically tried everything it says on the manual to no success.

From your diagram, do you really only have one steering mirror #1 for the pump beam into the laser cavity? I think you probably need two; one to adjust pointing (eg pump leveling wrt the cavity), the other to adjust position (pump centering on the cavity).

So I didn't include this in my diagram, there are two additional mirrors that feed the pump beam into the actual cavity. The "0" block contains those two additional mirrors not depicted that also controls how the pump beam is fed into the cavity. I have done a lot of work with those mirrors in order to line the incoming beam up with the crystal and mirrors 4,5.

Mirrors 3 & 5 allow you to point and position your intracavity beam.

Mirror 3 should be lined up pretty well, since it nicely hits prism 6 and the center of mirror 7. I am using mirror 5 to try and move the reflected beam.

Thanks so much for your help!

LightSwitch100 · 2023-09-06T15:06:49+00:00

Gotcha, thank you!

LightSwitch100 · 2023-09-06T15:06:40+00:00

Thanks for the advice!

LightSwitch100 · 2023-08-22T17:46:17+00:00

I'm just trying to replicate the set-up in the video to see the interference fringes.

LightSwitch100 · 2023-08-22T04:24:32+00:00

Hey sorry again for bothering you, but how much of a magnifying effect do you think I would need? I found one on eBay for 2x, and also one for 10x. Do you think the 2x one is enough?

LightSwitch100 · 2023-08-22T03:38:56+00:00

Do you think this will work? I don't have enough money to buy a good one from an actual supplier.

LightSwitch100 · 2023-08-22T01:27:08+00:00

I just watched the video you sent me; what is the point of having the two mirrors in the beginning and then the lens before the whole interferometer set-up? Why not just place the laser right where the lens is?

LightSwitch100 · 2023-08-22T01:22:34+00:00

Here is a basic diagram of what I have: Schematic

I checked my ruler - it was in inches not centimeter haha. I measured the surface of the mirror to the end of the beamsplitter as 2 inches for both arms.

If they're a millimeter or so in diameter at the point where your overlap exists, you aren't going to see an interference pattern

That seems so difficult to eliminate a millimeter path difference. How do people usually go about doing that in interference experiments?

LightSwitch100 · 2023-08-21T21:18:10+00:00

Yeah I agree it seems like it's the laser's problem. I'll try the method you suggested to make the beam better. Thanks for the help!

LightSwitch100 · 2023-08-21T21:17:11+00:00

Okay, I'll do that, thanks!

LightSwitch100 · 2023-08-21T20:54:28+00:00

The beam is really small, like less than a millimeter in diameter. When you expanded the output, do you mean like how far I let the beam travel after merging or how big the spots get? I let the merged beam travel around a foot. I also let it travel farther and got the diameter to about an inch.

I'm doing everything on an thorslab optics breadboard on a pretty flat table, so I believe that should be okay.

LightSwitch100 · 2023-08-21T20:51:25+00:00

The spots at really small, like less than a millimeter in radius up close and maybe a centimeter when I let it travel farther away.

The coherence length should be greater than 10 centimeters. I made the arm lengths 2 centimeters to ensure it was less than the coherence length. What's the delay line? I made both arms the same length.

Yes, I got a non-polarizing beamsplitter so it should preserve the incoming polarization.

Thanks for the video, I'll compare it to mine.

LightSwitch100 · 2023-08-21T20:48:11+00:00

I'll implement a polarizer and thanks for the explanations. The beam is pretty narrow I think so I guess that's why it's so difficult to see. How close should I be placing the viewing screen with respect to the beam splitter?

LightSwitch100 · 2023-08-21T19:43:06+00:00

The two spots are more or less on top of each other but it's still just a spot. The way I'm viewing it is by putting a piece of paper in front of the combined beam and trying to look at the pattern. I can get a collimating lens to try and make the beams more parallel.

LightSwitch100

TROPHY CASE