40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  ATF eLog  Not logged in ELOG logo
Message ID: 2671     Entry time: Wed Sep 22 16:40:19 2021
Author: Aidan 
Type: Laser 
Category: 2um Photodiodes 
Subject: Beam size measurements of the 2um beam on the PD 

I performed some occlusion measurements of the 2um laser going into the cryo chamber. For different values of dz on the collimating lens translation stage, I moved the power meter into the beam using it's translation stage by an amount dx.

One the beam was on the power meter (aperture = 5mm diameter) the power stayed constant for several MM before dropping again (indicating all the laser beam was on the power meter).

There was a big inrcease in incident power as dz was increased. This, and the constant power across the PD aperture, indicates that the beam is clipping or sees an aperture somewhere like the focussing lens (f=75mm) or further upstrean. I will review the expected beam size as a function of position, assuming the given NA fof the fiber.

 

Attachment 1: PD_measurement_layout.png  68 kB  Uploaded Wed Sep 22 17:48:17 2021  | Hide | Hide all | Show all
PD_measurement_layout.png
Attachment 2: PD_occlusion_measurements.txt  1 kB  Uploaded Wed Sep 22 19:03:36 2021  | Show | Hide all | Show all
ELOG V3.1.3-