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David Notebook: Difference between revisions
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==Daily Log==
'''8/8/14'''
I've abandoned the Thorlabs PDA10A in favor of the 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/sensisitivty 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.
Accounting for the new factors, chopped 633 power is now:
<math> (1.84*10^{-4} W/V) (A*Sensitivity) </math>
'''8/7/14'''
I'm having a hard time getting the Thorlabs photodiode to work. It's noisier and has a smaller sensor. I was previously able to detect a signal with it, but have had trouble the last few days. The UDT sensors one is much easier to work with, but the problem is that it's slower and so doesn't produce square waves when chopping above about 20 Hz. I need square waves so I can properly calculate the power, but there is too much noise at such low frequencies. Presumably the lock-in reading is linear with laser power even with non-square waves, so I'm just going to try to send in a beam with known power to the UDT photodiode and infer the relationship.
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