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projects:optics:log [2026/02/21 20:49] – [Day 2026-02-21 (k8ik)] k8ikprojects:optics:log [2026/02/22 18:33] (current) – [Day 2026-02-21 (k8ik, rahix)] rahix
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 ====== Lab Notes for Optics Experiments ====== ====== Lab Notes for Optics Experiments ======
  
-==== Day 2026-02-21 (k8ik) ====+==== Day 2026-02-21 (k8ik, rahix) ====
  
 We successfully coupled our shitty Aliexpress laser into the also high quality single mode fiber. However, we do see a beautiful beam but also what could be higher modes in the output, meaning the fiber is either broken at the end, the collimator has some issues or the fiber is indeed a multimode fiber. Most likely explanation right now: The fiber is a "broadband single mode fiber" for infrared (not specified) meaning it could allow for higher modes at 650nm. We successfully coupled our shitty Aliexpress laser into the also high quality single mode fiber. However, we do see a beautiful beam but also what could be higher modes in the output, meaning the fiber is either broken at the end, the collimator has some issues or the fiber is indeed a multimode fiber. Most likely explanation right now: The fiber is a "broadband single mode fiber" for infrared (not specified) meaning it could allow for higher modes at 650nm.
  
-{{:projects:optics:screenshot_from_2026-02-21_21-31-28.png?direct&400 |Ground mode of laser without collimator}}+{{:projects:optics:screenshot_from_2026-02-21_21-31-28.png?400|Ground mode of laser without collimator}} 
 +{{:projects:optics:signal-2026-02-21-212805_003.jpeg?400|Weird mode}}
  
-{{:projects:optics:signal-2026-02-21-212805_003.jpeg?direct&400 |Weird mode}}+We put a collimator on the other fiber end and aimed it at our camera to take some beam pictures. 
 + 
 +Wrote a little script which outputs the average intensity across the camera frame as a single number so we can tune the fiber coupling against it [[https://git.fa-fo.de/fafo/k8ik-stm/src/commit/3ecbe0b53f74b1d71ca9628accaadcc8cf0977f9/Calculations/live_intensity.py|live_intensity.py]]. 
 + 
 +Even after adjustment, only very little power coming out of the fiber.  After tuning, we readjusted the exposure of the camera to try imaging full beam pictures (but this only partially worked because the auto exposure setting of the camera is completely broken). 
 + 
 +First, here is a capture of a higher mode: 
 + 
 +{{:projects:optics:2026-02-22-fiber-beam-multimode.png?400|}} 
 + 
 +With a bit more tuning of the fiber coupling, we end up seeing some much nicer beam shapes: 
 + 
 +{{:projects:optics:2026-02-22-fiber-beam-01.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: