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David Notebook: Difference between revisions
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==Daily Log==
'''7/16/14'''
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
From page 69 in Josh's lab book #1, the 780 notch filter transmits about 19% at 633. This seemed low and I measured it with the HeNe as 88%. It seems like the curve for the notch filter is incorrect and I probably should recheck the cavity window and mirror curves with the spectrophotometer at some point. For now, I'm just going to manually measure everything with the HeNe and 780 TA.
633:
Notch Filter: 88%
Cavity Mirror (spare): 77%
Cavity Window (spare): 79%
Both: 61%
Or 65% for the pair when measuring through the actual cavity (took the square root since the generated 633 will only pass through one pair). I'll use this value.
29% through entire path past cavity (pickoff is first element; grating is last element; 633 bandpass filter is in) or 22% with a 780 notch filter in. The power for the 633 fluctuates somewhat, so these are not super accurate. The chopper cut the measured powers almost exactly in half as expected.
So with the 633 bandpass filter and the 780 notch filter, .61*.22 = '''13% 633 gets to the detector, or 6.5% with the chopper on.'''
For the 780 TA at 1W, with the chopper on there is 270 mW just before the cavity and 90 mW just after, so '''inside the cavity there should be 156 mW of 780.'''
I walked the 780 beam while ramping (a small 633 signal is still detected when ramping since it flashes at a relatively low harmonic of the 500 Hz chopper speed). Presumably finding the max power when ramping will be the same as when locking. Increased the signal to 5.8 nW at the detector (accounting for chopper--I'm always going to do this since we could turn the chopper off and have a 5.8 nW beam, it would just be hard to detect), which means 5.8/.13 = 42 nW in the cavity.
Our current efficiency then is 21 nW/156 mW = 1.35 * 10^-7 (use chopper-on value for 633 since we use the chopper-on value for 780).
Lasers are dangerous--we should set up a curtain around the computer and Wednesday afternoon lab laser tag should probably be cancelled.
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