HAM6 work today, we're done

Sheila, Terry, Haocun, Daniel, Nutsinee

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Summary: Dichroic flipped, measured some red losses (roughly 96% transmission from first dichroic to the bottom periscope on SQZT6), fixed the polarization issue (rotated in-vac half-waveplate by 7deg), aligned pump to OPO better (91% mode matched), and measured some distances from OM3 to AS_A and B. Ready for closeout ceremony

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Details:

Dichroic flipped and red losses

We flipped the first dichroic BS that was mounted backward (alog45288) and corrected the beam translation with the first and second dichroic steering. That went well. After that we locked the OPO on duel resonance at non-nlg temperature (51.2C), then measured red power just after the first dichroic and just before the bottom periscope on SQZT6. We took two sets of measurement:

Where	Total power (uW)	Seed blocked (measure green, mW)	Transmission
After 1st dichroic	173	18	-
Before bottom periscope	145	-	93.5%

Where	Total power (uW)	Seed blocked (measure green, mW)	Transmission
After 1st dichroic	160	18	-
Before bottom periscope	145	-	97.9%

 

Each measurement has +-3uW uncertainty. Note that before we still have green reflected after the first dichroic we had to block seed and measured green so we can subtracted that out from the transmission calculation. Green didn't make it all the way to the periscope. We just took the average of the two transmission measurements and called it 95.7%

 

Fixed Polarization Issue

For quite some time we were not able to get rid of the wrong polarization of the OPO refl (green) with just a half waveplate and the beam splitter cube on the SQZT6 alone but was able to get it down to <1% with a combination of half and quarter (alog43443). So we concluded that whatever came out of the vacuum was not linearly polarized. We turned the in-vac half waveplate by 7 deg and that solved the problem. I think the wrong polarization is now <1% of the total reflected power when OPO is unlocked, it jumped up by ~50% (of the OPO unlocked, wrong polarization power) when the cavity is locked. I'll have to get these number later. But it's all better that it used to be.

 

Pump alignment

Better than ever. The new fiber works so far. The data here has been darknoise subtracted. 88% total mode matched (all visible peaks taken into account) with the misalignment (10 mode) being just 4% of the 00. The forth peak on the far right (0.04) is likely mode mismatched and I'm not sure what 0.024 was, higher order mode wrapped around? The 80MHz modulation was unplugged when the scan was taken so there's no sidebands here. The wrong polarization peak exists between the 3rd and the 4th peak and it's ~1% of the 00 mode (visible when you zoom way in on StripTool, barely visible here). We only knew it's there because the Hansch-coullaud locking signal was visible on the OPO refl rejected.

OM3 to AS_A, B distances

Here I posted the number I was given as Haocun and Sheila did the measurement. Yes it's a mix of inches and mm. I'll let the conversion up to the user.

 

Still need to dump the close-out photos from the SD card. Will post that later.