(Dan, Koji, Masayuki, Alexa)
We measured the HAM6 septum angle using a laser pointer. We confirmed that there was no observable vertical component to the wedge angle, and then proceeded to measure the horizontal angle. We pointed the laser pointer such that the retro-reflected beam off the surface of the septum returned approximately directly back. Then we measured the distance from the second reflection to this point. This distance was 17mm. The distance from the laser pointer to the septum was measured to be 360mm.
This gives: wedge horizontal angle: 17/360 * 180/pi /2 /1.45 = 0.93 deg
In the equation above the factor of 2 comes from the optical lever effect. Meanwhile the factor of 1.45 comes from applying snells law with the index of refraction for glass and assuming the small angle approximation (see attached drawing).
This measurement was not extremely precise, but was close enough to the expected value of 0.75 deg.
In the attached picture, you will see the retro-reflected beam, which is almost ontop of the outgoing beam, and the second reflected beam. We used the ruler below to measure the separation.
Koji
As the things are getting more precise, I pulled out my old raytracing calculation for an wedged angle.
This gave me the wedge angle of 0.91deg.
This includes the new effect of
- Refractive index of fused silica at 632.8nm (n=1.457)
- Average thickness of the window ((0.948+0.870)/2 = 0.909" = 23.1mm)
- Non-orthogonal input angle
The primary beam is distant from the laser diode by -8mm while the secondary beam from the backsurface is at +9mm.
This condition was fullfilled when the wedge angle is 0.91deg.
The attached plots are:
Attachment1: The overview of the rays
Attachment2: Zoomed view of the optic part
Attachment3: Zoomed view of around the source
