Nick Brewer: Difference between revisions

Another problem we were having was not being able to see signs of spectral hole burning when the beams were focused in the crystal. I tried seeing spectral hole burning with several different beam diameters in the crystal. I used 10 uW of power and just changed the diameter of the beam. For each intensity I set the probe to a single frequency, then shined it on the crystal and watched the fluorescence through the side viewport until I could see that the beam make it all the way through and then blocked the beam so the hole wouldn't widen if the laser moved. I scanned the laser over a 20 MHz range with 100 kHz step size and 3 ms dwell time with the same 10 uW power. The spectral holes were between 1.53 and 24 MHz wide. Above intensities of .6 mW/cm^2 the scanning itself began to burn holes more quickly and at intensities of 2 mW/cm^2 I wasn't able to average any more because more than one scan widened the hole noticeably (even the first scan may have widened it but how else could you check to see if a hole was there?). Quickly after 34 mW/cm^2 of intensity a single scan was enough to just burn the entire scan width and no holes were seen. The papers about Pr:YSO operate at a much higher intensity than this so I will have to think more about how the other beams pump population back into the preferred ground state. Before each new intensity I heated the crystal up to 17 K and brought it back down to 5 K. This seemed to be the minimum temperature needed to erase a spectral hole.