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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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