Research Update August 29th

This is more of a note than an update of any kind, but I haven’t been able to sit down and write about what’s been going on research wise lately. The 461 nm laser system works wonderful now as long as you know you to finesse it. We went through the whole system and after passively stabilizing the diode as well as possible and rebuilding the doubling cavity we charted out the stable cavity modes that the diode has over a series of currents and temperatures. While the diode can scan mode hop free for ~30 GHz when things are JUST right, it still doesn’t follow the doubling cavity very far when locked. However, it follows it far enough.

The problem has been that while the laser scans over the resonance in the vapor cell the doppler broadening is about 300 MHz FWHM and the lamb dip is about 190 MHz FWHM. In short I took the cell over a broad range of intensities and alignments, we looked at the linewidth of the laser on a cavity, and we actively pumped (6 L/s) on the cell while running it all with no effect on the linewidth of the lamb dip. However, I noticed today that while we were pumping out on the cell when I first turned on the Sr, as the laser scanned across the resonance, not only could I see fluorescence all the way from window to window, but the brightest part of the fluorescence was concentrated on a very small segment of atoms. However, by the time we got to looking at thing on the scope the fluorescence was limited to the spray of atoms exiting the bottom part of the cell and the brightest part of the fluorescence was very spread out. This indicates that as the cell heats a Sr vapor that is mostly only Sr flows through the cell, however, when we get to temperatures where the Sr absorption is significant something else flows with the Sr.

Basically, watching the length of the fluorescence become limited across the cell is like watching the mean free path diminish. This is not good, and it happens even while pumping out on the cell which indicates that it is something that is generated with the Sr vapor. I’m going to convert the cell into hybrid jet/vapor cell design in an effort to overcome this problem and I’m going to refurbish it in the meantime. We have some lead left over in the cell, and I’m going to cut down the Sr in the cell big time to make sure that only the cleanest Sr is present.