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projects:optics:log [2026/02/22 12:04] – [Day 2026-02-21 (k8ik, rahix)] rahixprojects:optics:log [2026/05/17 14:14] (current) – ↷ Links adapted because of a move operation 14.162.15.137
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 ====== Lab Notes for Optics Experiments ====== ====== Lab Notes for Optics Experiments ======
 +These are the lab notes for our optics experiments.  Check the [[projects:optics:start|Laser Optics & Interferometry]] project page for an overview of the project.
 +==== Day 2026-04-04 (k8ik, rahix, many guests) ====
 +We presented our low-cost optics and the interferometer at EH23!  Watch our talk here: [[https://media.ccc.de/v/eh23-budget-beams-laser-experiments-in-a-hacker-lab|Budget Beams – Laser Experiments in a Hacker Lab]]
  
 +{{:projects:optics:2026-04-04-interferometer-eh23.jpg?600|}}
 +
 +During the event, our laser diode broke (well, rahix fed it too much voltage really) so we scrambled to disassemble a DVD drive and extract the red 650nm diode from it. We kept the collimation optics from the DVD drive and hot-glued the entire subassembly to an optics mount.  It took 3 attempts (3 DVD drives) to not immediately kill the new diode again.
 +
 +We managed to demonstrate the fringe movement from the piezo quite a few times.  We borrowed a different power supply to drive it.  This one seems to lead to a slow ramp-up of voltage (fringes move slowly when turning on) and an abrupt cutoff (fringes fall back very quickly when turing off).
 +
 +Stability was quite alright with the reduced isolation setup as long as nobody touched the table.
 +==== Day 2026-04-01 (k8ik, rahix) ====
 +Set up the interferometer experiment again, but with "analog" readout (i.e. just a viewing screen where the pattern is enlarged).
 +
 +Tried driving the Z-axis piezo of the STM head with +20V.  We can see movement!  When turning on the voltage, the pattern immediately jumps.  When turning it back off, it slowly drifts back to its original state.
 +
 +Eyeballed the movement to be somewhere below λ/2, so <300nm.  But for any proper measurement, we need to do digital readout again.
 +
 +Getting the laser stable enough to see the movement without noise is not easy. The mechanics hold up plenty fine.
 ==== Day 2026-02-21 (k8ik, rahix) ==== ==== Day 2026-02-21 (k8ik, rahix) ====
  
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 {{:projects:optics:2026-02-22-fiber-beam-01.png?400|}} {{:projects:optics:2026-02-22-fiber-beam-01.png?400|}}
 {{:projects:optics:2026-02-22-fiber-beam-02.png?400|}} {{:projects:optics:2026-02-22-fiber-beam-02.png?400|}}
 +
 +The curve does not look gaussian which is a bit worrying. Current assumption is that this is still a higher transversal mode that just looks close enough.
 ==== Day 2026-01-31 (k8ik) ==== ==== Day 2026-01-31 (k8ik) ====
 Aliexpress quality fiber and collimators arrived: Aliexpress quality fiber and collimators arrived:
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 Ordered a cheap fiber + collimator optics in hopes that we can use it to improve our beam profile (see [[#day_2025-09-06_rahix_q3k_hugo|2025-09-06]] notes). Ordered a cheap fiber + collimator optics in hopes that we can use it to improve our beam profile (see [[#day_2025-09-06_rahix_q3k_hugo|2025-09-06]] notes).
 ==== Day 2026-01-18 (k8ik, rahix) ==== ==== Day 2026-01-18 (k8ik, rahix) ====
-Built up two more mirror mounts and a special mount for the [[projects:stm|STM]] head (we want to measure piezo displacement).+Built up two more mirror mounts and a special mount for the [[projects:stm:start|STM]] head (we want to measure piezo displacement).
  
 Placed the camera into the interferometer to take a look at the interference pattern digitally.  Hello world: Placed the camera into the interferometer to take a look at the interference pattern digitally.  Hello world: