Oh, man. What a long past couple of months it has been and for a variety of reasons. Somehow we magically had set the laser JUST right all the time we had been running it before. It is actually an extremely fickle and ornery laser system despite the diode being AR coated. I’ll just list the basic changes we made to the laser system.
1. Replaced the doubling crystal. The AR coating on one end of the original crystal had been been damaged. We don’t know why but we suspect it was related to changing the crystal’s temperature. The new crystal was cushioned in several wraps of .1 mm thick purified lead foil to act as a buffer between the crystal and the aluminum mount.
2. Rebuilt the doubling cavity. Since we were aligning the cavity to a new crystal we took a moment to improve the cavity too. We made the cavity just the right length to be at the most stable beam waist for a 125 mm focal length lens. This required the cavity to be square instead of bowtie which wasn’t an issue because the mirrors are all flat. This also made the piezo scan twice as far as the cavity length with a FSR of 1.2 GHz.
3. Modified the doubling crystal temperature controller. Since we had been worried about the crystal damage having occurred due to temperature rates we installed an adjustable voltage regulator set at ~-18 V down from -48 V to ensure that the crystal temperature would never change faster than 10 C/min.
4. Floated both the doubling cavity box and the master laser system box on Sorbothane. Although the boxes float independently the alignment to the doubling cavity is surprisingly stable. The difference in mechanical noise isolation was immediately noticeable.
5. Mounted the diffraction grating on a piece cut at the right feedback angle on a cage mounted to the laser head face. I made the cavity as short as possible.
6. Placed a wavemeter in the master beam to watch stability and wavelength along with cavity coupling and blue output power. Verified the .1 nm/1 wavenumber FWHM of the cavity temperature.
7. Mapped out wavelength resonances of the diode as a function of current and temperature.
All of the work paid off in the end. The pictures and video show fluorescence in the vapor cell today. The infrared wavelength scanned 10849.13-.18 cm-1 to cross the atomic transition in the cell. With the cartridge heater at ~500 degrees C (cold end at ~200 C) fluorescence could be seen extending all the way across the cell, not just the central source even with chilled water running to cool the target area.
Here you can see fluorescence in the reflections off of both windows.
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