SHG Cavity: Difference between revisions
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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. |
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. |
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Once the position and focal lengths of the mode matching lenses are determined, the next thing to do is to place the crystal in the beam path where it will be in the cavity. |
Once the position and focal lengths of the mode matching lenses are determined, the next thing to do is to place the crystal in the beam path where it will be in the cavity. Use the two walk mirrors to center the beam as best as possible on the crystal. It is possible to see where the beam is hitting each face of the crystal with the IR viewer. Make sure the beam isn't reflecting off of the side of the crystal housing. Also make sure to keep the mode matching lenses as centered on the beam as possible. It is easiest to initially align the cavity if a to-scale print out of the beam path is taped on the table. |
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Place the output mirror (M2) and M3 where they should be according to the beam path layout. It is important to have the beam centered on the curved mirrors so that the mirror doesn't have to be tilted at an extreme angle to align the cavity. Use M2 and M3 to walk the beam along the beam path layout. Make sure it is also the right height off of the table. |
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Next place M4 and M1 in the beam path. Again, make sure the beam is as centered as possible on the curved mirror. Use these mirrors to shine the beam through the crystal again. If you were careful enough while placing the mirrors in the cavity you should be able to see at least one other dot (probably several dots) by the reflected beam. While looking at those dots, walk M4 and M1 to try to overlap the dots with the reflected beam. As you get more aligned you should see more dots begin to collapse in on the central spot. |
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* Picture of cavity design |
* Picture of cavity design |
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Revision as of 22:06, 21 May 2014
We can write our observations and procedures for the SHG cavity here. Also, it might be useful to have a list of any spec sheets.
Measurements
5/21/14
After detuning the temperature and aligning the vertically polarized light to the cavity we saw 5.5 mW of green light. The input power was 45 mW.
Alignment Procedures
- Picture of cavity design
- Matlab program for mode matching?
- Alignment procedure
Locking Circuit
- Circuit diagram
- Procedures for getting a clean error signal
- Procedures for locking
- Troubleshooting the circuit when lock isn't working well?