Geometry works

Well, something worked.  The new improved smaller pump size does indeed change the spectra, and in a sensible way.  As we predicted, the smaller pump leads to more typical-looking spectra for the tilted Fabry-Perots.  It seems plausible that this is because the pump beam sees less of a total difference in width from the top to the bottom of the active region of the FP.  In the limit that the pump beam has an infinitesimal radius, I suppose we would see a true FP spectrum no matter the tilt of the entire cavity.

So Maxime and I were very happy to see these results, and I spent the morning taking data to check on changes to the lasing thresholds of the true and tilted cavities.  The old and new thresholds can't be directly compared, since a smaller spot size with the same total pumping energy means higher pumping intensity, and we're not sure how much higher.  (It's difficult when your quantification of the spot size is "diameter's maybe two-and-a-half of those big tick marks? ish?")  We did some quick estimates, and I hope and think that I haven't burned out the cavities by sending too much energy at them, but we're not really sure what's going on with the emission amplitudes anyway.  The amplitude dropped significantly when we decreased the pump beam size, which could be explained by a smaller lasing region of the Fabry-Perot, but is at the very least inconvenient.  The data that I took don't show very clear thresholds, but I can probably make a decent estimate at least.

Both today and yesterday have featured tasty, free lunches, thanks to the physics department and LPQM in particular.  I think the lab group and school are winding down a bit as August holidays approach.  Clément is in fact leaving for his holidays now, so I bid him farewell this afternoon.  I'm quite grateful for all his help and for making me feel welcome in the lab.

Another feature shared by the past few days is rain.  My poor two-euro umbrella has decided that its proper state is inside-out, and I have to continually persuade it otherwise when I try to use it, so I often just walk in the rain.  Heedless of the weather, I went to the Musée d'Orsay after work yesterday.  After this visit, I think I have seen almost all of the works in the museum.  And they are beautiful works.  But my bluff was finally called by the ticket-taker at the front when I confidently presented my student IDs in lieu of a ticket - he kindly let me through anyway, but it turns out that one is supposed to live in the European Union for at least three months before one is entitled to the student privileges.  Well.  I confess that my bluffing days may still not quite be finished...

This evening was rather quiet.  I'm hoping to go see part of the Bastille Day parade tomorrow at the Champs Elysees, and maybe even visit the Pantheon or Sainte-Chapelle (finally) before meeting the others and heading out to Trocadero to watch fireworks over the Eiffel Tower.  Let's hope the weather cooperates!