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David Notebook: Difference between revisions
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==Things to Do/Check==
*Shape 780 beam with prism pair or send it through a fiber
*Translate 780 lens before cavity to adjust focus
*Use beam chopper on 780. <strike>Pump down cavity and put in new D2</strike>. Translate iris in front of PVC pipe to see if signal is from a beam or scatter. Try different filter combinations. <strike> Check characteristics of 633 filter--does it let through 1555?</strike> <strike>Calculate angular positions of second order diffracted beams--are they close to where 633 should be?</strike>
*Why is 1064 current driver fluctuating?
*Measure 780 power before and after cavity; see changes with cavity piezo
==Daily Log==
'''7/
In addition to increasing absolute power of the 633 generated, we also want to improve the conversion efficiency. The 780 beam is larger than the 1064 in the cavity, so this will greatly limit efficiency. Maybe try a prism pair to reduce anisotropy or a fiber to make beam Gaussian--power will be reduced, but efficiency should be higher.
Spent the last 2 days setting up the beam chopper and a lock-in amplifier for it. It works very well and after sending the HeNe through 2 irises I could easily measure it 1 nW. I thought I was seeing a signal at one point that only appeared when locking when the 780 was one, but I haven't been able to replicate it yet. It's difficult to optimize the settings on the amplifier since I can only lock the 1064 for a second or two at a time. Is there some way I can do it while ramping instead? ▼
Lasers are dangerous--we should set up a curtain around the computer and Wednesday afternoon lab laser tag should probably be cancelled.
'''7/15/14'''
Further 780 alignment optimizations have raised the 633 power at the photodiode to 1.9 nW (3.8 accounting for beam chopper). I put in a 780 notch filter right before the photodiode to make adjusting the 780 alignment easier--the scattered 780 at the photodiode changes when adjusting its alignment, which washes out a change in the 633 signal. Hopefully this will make changes in 633 easier to detect.
'''7/14/14'''
Power flickered today and the temperature controller for the TA shut off and the TA got to 40° C before we realized. It seems undamaged. The controller also shut off later again--maybe another power flicker, or is it broken? Keep an eye on it...
'''11:43 am''' I see something! I'm almost positive. Is champagne allowed in lab? What time does happy hour start at the library? When locking the 1064 beam with the 780 on, there is a noticeable jump in signal that is not present with the 780 off. Turning on/off the 780 changes the DC offset of the signal, but the jump when locking is about 10 times higher when 780 is on. The signal is clearly correlated with the lock.
Things to try this afternoon--remove photodiode and make sure 633 flashing is visible with current alignment, remove 633 filter--offset should change, but locking signal shouldn't change much (check how much 633 it should pass), move 633 filter to the front of the detector--does this reduce DC offset when turning 780 on/off?, turn down 780 power--does locking signal decrease linearly?
'''7/11/14'''
▲Spent the last 2 days setting up the beam chopper and a lock-in amplifier for it. It works very well and after sending the HeNe through 2 irises I could easily measure it 1 nW. I thought I was seeing a signal at one point that only appeared when locking when the 780 was one, but I haven't been able to replicate it yet. It's difficult to optimize the settings on the amplifier since I can only lock the 1064 for a second or two at a time. Is there some way I can do it while ramping instead?
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