Helios - Michaelson Interferometer

✧˚⋆ DEVLOG 7: I have finally succeeded in setting up the photodiode system! It now outputs signal value ranging from 97-350, and filtering out almost all noise. This required re-programming the way in which output signal is detected, as heavy 120Hz noise was present, and rewiring until the best result (so far) was acheived. This allowed me to complete the project’s main goal: magnetostriction effects observed in a nickel rod! This is despite amplification still not being fully maximized. (theo. max: 1023)

To test this, I wrapped a 25ft copper wire around the solenoid cover and connected it to a DC power supply. As current is turned up, the photodiode signal has been decreasing repeatly. (See photo - output decreases by ~1-2)

In the pulse test, it is also shown to decrease instantaneously, and when the photodiode is covered, no parasitic effects from the current are present, leading me to believe that the observed effect was truly caused by fringe shift due to magnetic shrinkage caused by the solenoid.

For this reason, this may very well be my last devlog! There is still room for improvement in fine-tuning the amplification system, but the full functionality of every component has been demonstrated. It however doesn’t mean I’m done with the project at all after shipping - I can try out rods with different metals and higher currents with amplified signal to get and compare ‘true’ quantitative data in the future!
Check out README.md for more details!

✧˚⋆ DEVLOG 6: The last three weeks of my project have been subject to great stagnation - However, I now have been able to photograph fringes! (See photo 2).

Unfortunately, they appear to be a mix of Michaelson fringes and lens (Newton) interference (remain when one mirror is blocked) - the latter kind is useless to measure wavelengths, so we now only want stronger Michaelson fringes, which appear more as bands or arcs of light. (noticeable now yet currently hard to image)

To come to this, I’ve had to reprint the LMB and LDM to allow translation (and some rotational) alignment with screws, reworked the mirror mounting system screws (removing bolts) and reprinted the solenoid cover from Devlog 5. This has allowed my alignment to be much more precisely adjustable - it has also made it more tedious to align. To this effect, I added ruler and protractor markings for the MMM, LDM and LMB to serve as alignment guides, and since, I’ve added guides to the MMM to make sure the mirror follows more linear guides.

These changes insure that I can now very finely adjust angles and mirror distances prop. to beam splitter to be equal - which is what we need!

For acronyms list, and further info on how the alignment process is done, check out the project GitHub! :)

✧˚⋆ DEVLOG 5: Beamsplitter is here! I’ve finally started proper alignment testing by putting together the optical components into their respective mounts.
However, no interferometry yet - the BSM had to be reprinted to fit the beamsplitter, and my SMB mirror mount was 4mm too low, which made me reprint a slightly taller solenoid cover..

Every time I had to print the solenoid cover, severe noodling would happen in at least one section of this component. After 4 iterations, i decided to use the least damaged one, and now, my lasers at least somewhat align to the mirrors!

I’ve now made additional supports for the laser and lens allowing for slight translation to make precise alignment a much easier task. For more info and acronym list, check out the README on GitHub :)

✧˚⋆ DEVLOG 4: I’ve finally been able to complete, print and assemble all CAD mounts! Attached in the image below is the mounting system in the interferometer’s calibration phase. The assembly process took a disgusting amount of time, as most parts had to be re-iterated upon, either due to screw alignment, screw dimensions or linkage strength.

Tolerances were a recurring issue with the components — I had to drill the mirror mounting systems in the MMM and SMB (new acronyms to be found on my GitHub btw!) which served as a wake up call on wearing proper safety equipment, multiple times.. my screen protector is still irreparably cracked from the PETG-CF shards, and my hand felt much of the same to say the least lol.

Oh, and no more DVD drive laser components - I have switched to a proper (Class II) laser to conduct my experiments.

However, things are looking up, and the build quality is now solid! I am waiting on the final component to arrive (beamsplitter) before assembling the final system. same time next week? :)

✧˚⋆ DEVLOG 3: I’ve received most of the parts, so NOW, I’ve been able to work on the real electronics and design the 3d CAD mounts - my full design is therefore almost complete! (I have a bad habit of saying that lol)

One thing which was particularly tricky was the solenoid mirror mount, which went through multiple different iterations. I had to find a way to encorporate the advantage of the screw-plate mounting system and free suspended motion, and my design eventually (…) was able to accomplish this using a counterbalance!

Then, while messing around with the Uno R3 kit, I also managed to get the laser diode, which I disassembled from my old laptop’s DVD drive, to be functional! It’s not collimated by its lens anymore, but it’s a step in the right direction. I’m sure i’ll be able to find a workaround someway, right? right? :’)

✧˚⋆ DEVLOG 2: Based off measurements from the ordered parts (which took about 3 days to document in detail in terms of every option and decision), I created a precise, 1:2 scale top down technical drawing!
This was rather tedious - I only had a straight edge, pencils and 8cm triangle ruler available, as I am currently traveling.. The detailed drawing shows the interferometer in the calibration phase, so I made another sketch showing how all the components interact with one another in both phases too.
Check out Devlog 1 for photodiode circuit details (they aren’t shown on the lower drawing!) :)

✧˚⋆ DEVLOG 1: Aside from (lots…) of documentation, I created this TIA photodiode circuit in Tinkercad to mirror the one which will measure the fringe shifts in my interferometer.

Safe to say, this was not all smooth sailing - the components were challenging to wire correctly (particularly the op-amp) and the range of output values was.. disheartening at times (512-513 or 0-2) but I finally got it to an amplified degree!

One of the solutions was simply flipping the polarity of the photodiode lol. It now outputs values from 0-1021 depending on the inverted light intensity, which is optimal for my project as the effect of real-world noise will now be much lesser than without the amplification system. I’ll keep you guys updated! Check out my github or ask me for more info :)