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Nick Brewer: Difference between revisions
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'''<big>2/16/15</big>'''
The idea of using the UV diode to 'reset' the 7F0 ground state seems to not work. We had hoped that by shining the UV light on the crystal we would pump the atoms to a highly excited state. Then when they fell back down to the ground state they would be evenly distributed between the three hyperfine levels. I focused the UV light onto the crystal and positioned it so the fluorescence was maximized. I burned a hole the usual way and then shined the UV light on the crystal to try to erase it. It didn't seem to do anything even when left on for an hour. I tried to erase the hole with the UV light both while the probe beam was still scanning so I could see if the hole was diminishing and while shutting the 527 nm light completely off. The UV diode is a 2 Watt diode and comes with an adjustable collimating lens. I adjusted the lens so that instead of collimating the light, it was focused on the crystal. The focused light though is still wider than the crystal so maybe there isn't enough intensity for this to be effective. I was able to reset the atoms by heating the crystal up to between 40K and 50K. I did this by adjusting the set point on the temperature controller. It only took about 5 minutes to heat up and cool back down, so maybe this isn't a terrible way of doing things if we need to.
We might not even need to reset the levels. I was pretty consistently able to sweep out a hole, back burn in a peak with the control beam and the repumper, sweep the hole again and repeat the back burning. After realigning the beams, I was able to repopulate the center of a swept out hole about 50%. This was looking at the absorption, not the fluorescence. I was looking at the absorption of the probe beam at around .4 mW and it still looked like I was putting around 50% back in the hole. This seems like a pretty high power, it didn't seem to sweep the hole back out, but I did decrease the dwell time on the sweep from 10 ms to 3 ms so maybe it isn't on long enough. Maybe this is still too low of a power and we are still getting fully absorbed at the edges of the scan.
Also, those mystery mirrors that came from surplus that we thought worked at 45 degrees for green were not reflecting very well for the control and repumper. There was about 8 mW before the two mirrors and only about .2 mW after. Maybe I didn't have them set up at 45 well enough, because they are working for the probe beam fine. Instead of messing around with them I just replaced them with silver mirrors.
'''<big>1/30/15</big>'''
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