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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  | Show | Hide all | Show all
Attachment 2: PD_occlusion_measurements.txt  1 kB  Uploaded Wed Sep 22 19:03:36 2021  | Hide | Hide all | Show all
	Length from Focussing lens to POW METER = 80mm															
																
																
2.73mm			3.73mm			dz	4.73mm	5.73mm	6.73mm	7.73mm	8.73mm	9.73mm	10.73mm	11.73mm	12.73mm	13.73mm
																
dx (0.01mm)	PM(uW)		dx	PM(uW)		dx	PM(uW)	PM(uW)	PM(uW)	PM(uW)	PM(uW)	PM(uW)	PM(uW)	PM(uW)	PM(uW)	PM(uW)
60	191		40	3		200	241.9	272	305	348	395	454	523	605	697	798
50	189		50	7.25		175	241.7	270	307	346	394	452	519	595	685	777
35	181.7		65	23.6		150	234.5	262	296	333	377	432	492	563	645	727
20	169		75	85.5		130	218.8	243.6	274	308	356	395	445	507	579	657
... 7 more lines ...
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