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 40m Log Not logged in Message ID: 2909     Entry time: Mon May 10 22:25:03 2010     In reply to: 2907     Reply to this: 2910   2912
 Author: Koji Type: Update Category: Green Locking Subject: Green Laser Beam Profile

Hey, what a quick work!

But, wait...

1) The radius of the beam was measured by the razor blade.

2) The diameter of the beam (13.5% full-width) at each point was measured by Beam Scan. The one at z=~7cm was consistent with 1)

3) The data 2) was fitted by a function w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2). This is defined for the radius, isn't it?

So the fitting must be recalculated with correct radius.
Make sure that you always use radius and write with a explicit word "radius" in the record.

Quote:

Kiwamu and Kevin measured the beam profile of the green laser by the south arm ETM.

The following measurements were made with 1.984A injection current and 39.65°C laser crystal temperature.

Two vertical scans (one up and one down) were taken with a razor blocking light entering a photodiode with the razor 7.2cm from the center of the lens. This data was fit to

b + a*erf(sqrt(2)*(x-x0)/w) with the following results:

scan down: w = (0.908 ± 0.030)mm  chi^2 = 3.8

scan up:      w = (0.853 ± 0.025)mm   chi^2 = 2.9

giving a weighted value of w = (0.876 ± 0.019)mm at this distance.

The beam widths for the profile fits were measured with the beam scanner. The widths are measured as the full width at 13.5% of the maximum. Each measurement was averaged over 100 samples. The distance is measured from the back of the lens mount to the front face of the beam scanner.

 distance (cm) vertical w (µm) horizontal w (µm) 3.2 ± 0.1 1231 ± 8 1186 ± 7 4.7 ± 0.1 1400 ± 4 1363 ± 6 7.4 ± 0.1 1656 ± 5 1625 ± 9 9.6 ± 0.1 1910 ± 10 1863 ± 9 12.5 ± 0.1 2197 ± 8 2176 ± 8 14.6 ± 0.1 2450 ± 12 2416 ± 10 17.5 ± 0.1 2717 ± 12 2694 ± 14 20.0 ± 0.1 2973 ± 16 2959 ± 8 22.4 ± 0.1 3234 ± 12 3193 ± 14

This data was fit to w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2) with lambda = 532nm with the following results:

For the vertical beam profile:

reduced chi^2 = 3.29

x0 = (-87 ± 1)mm

w0 = (16.30 ± 0.14)µm

For the horizontal beam profile:

reduced chi^2 = 2.01

x0 = (-82 ± 1)mm

w0 = (16.12 ± 0.10)µm

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