NRC-INMS Summer Project

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
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"Imagination will often carry us to worlds that never were. But without it we go nowhere." ~Carl Sagan

ISI Brno presentation

I had just attended a very enjoyable talk by Dr. Bretislav Mikel part of the Coherent Optics group of The Institute of Scientific Instruments in Brno. Their institute is quite similar to our Institute for National Measurements and Standards except for the fact that their do not concentrate only on metrology or calibrations. Instead, as the name might suggest, they develop techniques and instruments that can be used in other fields, mainly precise measurement standards used in labs and industry. The ISI is run through the Academy of Sciences of the Czech Republic which the speaker compared to NRC -- Funny enough Dr. Mikel said that the organization concentrates more on pure research something that the NRC is starting to deviate from.

The talk gave an overview of the different projects run at their institute -- the list is quite varied but all topics were very interesting. There are three groups working at ISI: Electron Optics, Magnetic Resonance and Bioinformatics, and Coherent Optics. The first group works mainly with microscopy for the detection of nano-size materials as well as some other microscopy techniques. The MRB group deals with superconductivity and conduct some medical research. The Coherent Optics group was the one that was covered in more detail.

Interestingly enough one of their specialties is what I have been working on this summer -- Laser locking to gas filled cells. They produce standard cells filled with acetylene or iodine but are capable of filling the cells with other gases. The usefulness of these cells is that their all one to lock the laser to a specific obsorbtion energy of the gas. Iodine is used for the visible spectrum, while acetylene allows tuning to the communication region. ( Here is paper on the topic and this is an example of the Pound Drever Hall technique used in frequency locking to a cavity).

The CO groups also works on precise distance measurements and have developed several instruments for determining the absolute length of an object (on the nano-scale) or obtaining a representation of a shape in all degrees of freedom. However, one of the topics that I found to be the most intriguing was the Micro Optical-manipulation Techniques project. Aside from the traditional optical tweezers and scissors this group works on optical sorting. The idea is that an object can be moved simply by the use of light-- Okay, granted a small object. The group managed to trap nano-sized balls in an interference pattern (they call this an optical conveyor belt) and move the balls with another laser light that would not disrupt the fringes. The reason for the movement of the balls is that they act as lenses and cause the light to bend. The change in momentum in the photon is translated to the ball and thus causes movement. Now, the sorting part: The group managed to move balls of different size in different directions. This could be advantageous in future nano research and frankly it is pretty cool.

The research done at ISI seems to be quite interesting and there are many exciting developments in the nano-scale manipulation research. Now to go find a laser...

Mr. V
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"Imagination will often carry us to worlds that never were. But without it we go nowhere." ~Carl Sagan