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 40m Log Not logged in Message ID: 2933     Entry time: Fri May 14 16:14:37 2010     In reply to: 2916
 Author: Kevin Type: Update Category: Green Locking Subject: Green Laser Beam Profile

 Quote: Strange. I thought the new result became twice of the first result. i.e. w0=32um or so. Can you explain why the waist raidus is estimated to be three times of the last one? Can you explain why the measured radius @~70mm is not 0.8mm, which you told us last time, but is 0.6mm? The measurements have been done at the outside of the Rayleigh range. This means that the waist size is derived from the divergence angle theta = lambda / (pi w0) At the beginning you used diameter instead of radius. This means you used twice larger theta to determine w0. So if that mistake is corrected, the result for w0 should be just twice of the previous wrong fit.
I was off by a factor of sqrt(2). The correct fit parameters are

for the vertical beam profile:

reduced chi^2 = 3.28

x0 = (-87 ± 1) mm

w0 = (32.59 ± 27) µm

for the horizontal beam profile

reduced chi^2 = 2.02

x0 = (-82 ± 1) mm

w0 = (32.23 ± 20) µm

In the following plots * denotes vertical data points and + denotes horizontal data points. The blue curve is the fit to the vertical data and the purple curve is the fit to the horizontal data.

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