Well, this summer was definitely filled with a good deal of learning and developing many skills. It was quite interesting working in a physics lab and trying to figure out solution and the required set up for an experiment. But, I guess all good things come to an end...and this one ends with a presentation that I have to give tomorrow morning. So I thought of sharing it here.
It will be a good opportunity to overview before tomorrow. The basic idea of my project is frequency stabilizing a laser to an absorption line for acetylene gas. This is useful because the frequency of the rotational vibration lines that I am locking to fall in the telecommunication frequency band and allow for the measure of absolute frequency. Above is a picture of the absorption dip observed for the P(16) line of acetylene.
The system used the idea of a fabry-perot cavity, which acts to select for a frequency. The Pound-Drever-Hall technique is used with a servo to lock to the cavity. The idea is that radiation is sent back from the cavity and it can be detected and the laser modulated to stay at a particular frequency using a discriminator signal.
The same idea of using a servo coupled with a discriminator signal is used to lock to an absorption line in acetylene. 
To test the system, a second system, locked to the same frequency, was used. The frequency of the second system was offset by 80MHz and a heterodyne beat was observed. This test is a lot like when two sounds are playing at the relatively close frequency and beat sound is heard. The difference between the two systems was found to be ~5kHz with an error in the 10^-11 range. Considering the fact that the cell is overfilled, which is less than optimal due to Doppler broadening, this result is quite good and falls well into the international standards for such cells. As you can see in the picture to the left, the line width of the beat signal is very narrow and demonstrates that the systems are almost at par.
Overall a productive summer which yielded great results and great experience. Hopefully, the presentation goes as smoothly!
Mr. V
_________
"Imagination will often carry us to worlds that never were. But without it we go nowhere." ~Carl Sagan
No comments:
Post a Comment