After Keita found that the Ophir PD300-3W-V1 power meter we were using had large angle and spot position dependence (alog 59372), we brought a Thorlabs S130C to finish taking OPO measurements. Conclusions from today's angle and spot position testing is that it is much better and can be trusted to better than 1%. Will add comment with method later.
- Horizontal spot position dependence +/- 0.5%
- Graph here
- All positions fully on active detector area (9.7 mm x 9.7 mm) were between 106.4 and 107.4uW when normalized using Ophir power meter measurement giving +/- 0.47%.
- Yaw angular dependence +/- 0.2%
- Graph here
- All positions within +/-10deg of normal (we think easily achievable without using retro-reflection) were between 107.54 and 107.97uW when normalized using Ophir PM giving +/-0.20%
Data and charts recorded on this google doc. The set up was very similar to Keita's measurements. I initially lined up power meter displacement to be central by eye and angle by using the retro refection at a lever arm 260mm. Measurements are using angular and translation stages so very precise.
Main difference to Keita's set up was I set up a 50/50 beam splitter to monitor the laser power using our Ophir Power meter. Photo of setup attached. It drifted a little over the measurements so I normalized using PS130C / (Pref / Pref(0)). Note that I used to first reference measurement taken, Pref(0), to scale all measurements to PS130C because the beam splitter wasn't exactly 50/50.
The S130C power meter was used without filter. There wasn't a clear beam retro-reflection with filter.
The S130C power meter has a low max average power density of 20W/cm2 with the filter. This means a 100μm radius beam should have a max power 6mW with filter. It is unclear if more will damage the filter/meter and what should be used as a mx w/o filter, I am following up with Thorlabs. To be conservative, I minimized power from NPRO using the wave plate and added a Neutral density filter (ND10A) which has 10% transmission. Misaligned slightly to stop back-refection. Measured power 100-125μW.
I photographed our beam using the wincam to understand the size of the beam: waist ~200μm. It was ugly but this doesn't matter as is cleaned up in fiber before reaching VOPO. See attached image.
I've also attached pitch data.
- Pitch angular dependence +/- < 0.2%
- If we thought it was important we could adjust the mount and change the orientation of PM to easily measure vertical displacement and pitch angular displacement but the results so far show this PM can be trusted to better than 1% without further testing.
