David Notebook: Difference between revisions

'''8/10/14'''

Running more tests with the PDA36A. I checked it from 5 to 100 nW as measured on the power meter (again though, I'm not very confident in it's measurements at the nW level--lots of fluctuations and hard to get 0 offset) and found the response to be logarithmic when the gain was set to 0 dB as I was using it on 8/8/14. I don't think this will work unless I can more accurately measure nW level beams with the power meter and then make a good regression equation for a logarithmic response. I then repeated these measurements with the gain at 60 dB and found the response to be much more linear. Data is [https://wiki.physics.wisc.edu/yavuz/images/2/29/Thorlabs_pda36a_response.xlsx here]. Maybe I can find the best gain setting that gives the most linear response at these powers and get a good linear fit at slightly higher beam powers and extrapolate to the single nW level event though I can't measure those powers well with the power meter.

'''8/8/14'''

I've abandoned the [[Thorlabs PDA10A Si Amplified Fixed Detector|Thorlabs PDA10A]] in favor of the [[Thorlabs PDA36A Si Switchable Gain Detector|Thorlabs PDA36A]]. It's fast enough to produce square waves at 400 Hz, and has a much larger sensor. It also has a lower minimum gain, which seems to work better when used in conjunction with the lock-in. I still should try to check if the response is linear at low powers. Ostensibly though, using it's different gain/sensitivity values and following the same analysis from 7/18/14, I get about 3.2 nW of chopped 633 power at the detector. This is still an efficiency of around <math> 6*10^{-7}</math> although it looks much brighter than before. Maybe one set of power measurements is somewhat inaccurate. I really don't trust the photodiodes to gives accurate linear responses at such low laser powers.