User:Anthony Salvagno/Notebook/Research/2010/04/01/Laser Issues Resolved

Pranav and I looked into the laser issues we were having when the laser gets into higher power regimes (above 1W). We noticed a while ago that the beam looked more or less like a donut indicating higher order modes at higher powers. Koch figured it might have to do with heating so we looked into it.

Approach and Results
We wanted to check how the laser reacts when cooled and when hot. We let the laser get hot and took pictures every half watt from 1W up to 4W. We then took an aluminum block that we stored in the freezer and put it on the laser. We allowed the laser to cool for about 5 min and then repeated the picture taking process with the block on the laser. In between the two processes, we took pictures with the laser stable at 4W and adjusted the AOM to make sure it wasn't an AOM issue. We took an image every volt starting at 2V up to 5V. Those images can be seen below with captions about each picture.  It is quite remarkable flipping through the images quickly you can see the "hole" in the laser intensity become more prominent and then when it is cooled you can see it looks good. Also it is startling to see the two images side-by-side at the end with their respective beam profiles. Pretty cool stuff.

Further Testing Tomorrow
So tomorrow Pranav and I are going to take images of the hot laser and the cold laser several times to see if these images are reproducible. If this is the case we want to cool the laser and then allow it to come to room temp (and beyond) taking images of the beam profile with temperature recording at that moment. This will allow us to see if there is an optimum temperature and at what T the laser starts looking really bad.
 * Steve Koch 18:39, 1 April 2010 (EDT): Awesome! For tomorrow, you should also look at the sum signal response and the image of the reflected tweezers.  That will give you more information about if it's fixed.  Good work!
 * Steve Koch 18:39, 1 April 2010 (EDT): Also, power spectrum. You could use AOM to keep power at some fixed level and check that the power spectrum does not change as laser power is increased (when cooled).
 * Steve Koch 18:42, 1 April 2010 (EDT):Also, I notice that the beam is still not perfect, even when cold. But definitely much better.
 * Steve Koch 18:44, 1 April 2010 (EDT): As for heat sinks, I'd ask Andy for suggested sites. You can also ask Coherent if they have a recommendation.  Without peltier, it will be pretty cheap.