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Entry  Sat Apr 17 18:30:12 2010, Zach, Update, Green Locking, 1W NPRO output profile profile_fit_4_17_10.png
    Reply  Mon Apr 19 11:31:04 2010, Aidan, Update, Green Locking, 1W NPRO output profile 
Message ID: 2807     Entry time: Mon Apr 19 11:31:04 2010     In reply to: 2804
Author: Aidan 
Type: Update 
Category: Green Locking 
Subject: 1W NPRO output profile 

Quote:

 Koji asked me to take a profile of the output of the 1W NPRO that will be used for green locking. I used the razor-scan method, plotting the voltage output of a PD vs the position of the razor across the beam, both vertically and horizontally. This was done at 6 points along the beam path out of the laser box.

I determined the beam spot size at each point by doing a least-squares fit on the plots above in Matlab (using w as one of the fitting parameters) to the cumulative distribution functions (error functions) they should approximate.

I then did another least-squares fit, fitting the above "measured" beam profiles to the gaussian form for w vs z. Below is a summary.

It seems reasonable, though I know that M2 < 1 is fishy, as it implies less divergence than ideal for that waist size. Also, like Koji feared, the waist is inside the box and thus the scan is almost entirely in the linear regime.

profile_fit_4_17_10.png

There is a clearly a difference in the divergence angle of the x and y beams - maybe 10-20%. Since the measurements are outside the Rayleigh range and approximately in the linear regime, the slope of the divergence in this plot should be inversely proportional to the waists - meaning the x- and y- waist sizes should differ by about 10-20%. You should check your fitting program for the waist.

 

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