The profile of the Innolight 2W was previously measured by measuring the reflected beam from the front surface of a W2 window (see entry). To investigate thermal effects, Rana suggested also measuring the profile of the beam reflected from the back surface of the W2.
I used the same setup and methods as were used in the first measurement. The mirror was moved so that only the beam reflected from the back surface of the W2 was reflected from the mirror. This beam was reflected from both the front of the mirror and the back of the mirror. An extra beam dump was positioned to block the reflection from the back of the mirror.
This measurement was made with 2.004 A injection current and 25.04°C laser crystal temperature.
The data was fit to w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2) with the following results
For the horizontal beam profile:
reduced chi^2 = 5.1
x0 = (-186 ± 6) mm
w0 = (125.8 ± 1.4) µm
For the vertical beam profile:
reduced chi^2 = 14.4
x0 = (-202 ± 11) mm
w0 = (132.5 ± 2.7) µm
In the following plots, the blue curve is the fit to the vertical beam radius, the purple curve is the fit to the horizontal beam radius, * denotes a data point from the vertical data, and + denotes a data point from the horizontal data.
The differences between the beam radii for the beam reflected from the front surface and the beam reflected from the back surface are
Δw0_horizontal = (12.8 ± 1.6) µm
Δw0_vertical = (8.5 ± 2.9) µm
So the two measurements are not consistent. This suggests that the passage through the W2 altered the profile of the beam.