SHG Cavity: Difference between revisions

 

==Alignment Procedures==

 

The first thing to do is to measure the beam profile and figure out what sort of lenses need to be used to mode match the beam. From what I've experienced, it's easiest to mode match the cavity with two lenses. Both lenses together determine the waist size and position and both need to be adjusted to best mode match the cavity. However, it seems like lens 1 moves the position of the waist more than the size of the waist and lens 2 changes the waist size more than the position. I find it easiest to have both lenses on translation stages.

 

In order to generate the most green the cavity needs to be tuned for 1055 nm light at the correct polarization. The best way to do this is to optimize the polarization so that the most green is generated, then detune the temperature (~2 degrees C should be enough). The generated green beam should decrease in intensity. Now by looking at a transmitted IR beam, the cavity can be optimized for the IR wavelength that needs to be doubled.

 

Once the IR peaks are optimized, the crystal temperature can be properly tuned. The output should be a bright green beam that can be easily locked (as described below). The locking scheme being used is the [http://ac.els-cdn.com/0030401880900693/1-s2.0-0030401880900693-main.pdf?_tid=d6c341da-e1f5-11e3-a208-00000aab0f27&acdnat=1400793353_c50b897ab97c50bf8a2338785cc28832 Hanch Couillaud] method. This method requires a polarization selecting element in the cavity (in this case the PPKTP crystal) and an input beam that has a polarization at some angle to the resonant polarization. For this reason the polarization of the input beam will need to be slightly rotated from the optimal angle.