## Weekly Progress Report

### June 7th, 2002

This week has been my first week here at SUNY Stony Brook participating in the Physics NSF Research Experience for Undergraduates. I'm working in the Laser Teaching Center here in the basement of the Physics Building. Over the course of this last week I've had an introduction to the lab and the people here as well as the computer system. I've been setting up this site with the assistance of Dr. Noe over the past few days. I also used a Michelson interferometer to view the visibility fringes in sodium light. An extremely important concept beyond the alignment of the interferometer is that the difference in the path lengths of the mirrors used must be within the coherence length associated with the wavelength spread of the sodium doublet. This coherence length can be calculated as the square of the average of the wavelengths divided by the separation of the wavelengths. After some tweeking I was able to get near circular fringes and view the process of washout caused by the interference patterns of each of the fringe patterns created by the wavelengths associated with the sodium doublet. As a result of this I was able to attempt to calculate the wavelength separation of the doublet and I came up with a result of approximately 6.1 angstroms, though the accepted value is more near 6 angstroms.

### June 14th, 2002

I've been studying possible projects in nonlinear optical effects over the past week. Some ideas I've gotten have been from the article 'Experimental Observation of Wave Chaos in a Conventional Optical Resonator' from the Feb. 11th, 2002 edition of Physical Review Letters. I put up a link to the XPPAUT homepage in my weblinks section. It's a very useful differential equations program and is able to do Poincarre maps as well as the 2-d and 3-d plots. A new feature has been the color animations which are fun to play with. In my sodium fringes news: I'm still trying to find a method to project the image of the fringes onto a screen so that they may be detected by a photomultiplier. Any suggestions would be appreciated.

### June 21st, 2002

A camera was used to try to detect the sodium fringes, but the source was too bright for the camera to be able to pick them up. I've hooked up a variable DC source to a HeNe laser and started to take some data as to the properties of the light from an underpowered laser. Below a certain level the laser goes from continuous operation to alternating operation with a flickering state. Below yet another level the flickering state occurs on its own before going into a state where the flickering alternates with inoperation. I'd like to see if there's any type of pattern to this alternating state or if it may be chaotic at any level. Eventually this alternating settles down into complete inoperation. I've taken data for the case where there is no limit on current and the voltage is slowly lowered. Today I plan to take data for the case where there is no limit on voltage and the current is slowly reduced. Later I plan to adjust both to appropriate levels. There exists a definite hystresis related to the state of operation of the laser with regards to the adjustment of the voltage and current. I've posted some data here.

### June 28th, 2002

The design and use of a grating spectrometer was studied over the course of this week. The spectrometer consists of two gold concave mirrors of 30cm focal length. The source is placed 30cm from the first mirror while the detector is placed 30cm from the second mirror. Along the path between the mirrors a grating is positioned. The grating reflects different wavelengths of light at different angles. This is then projected onto the detector, which consists of a one dimensional array of photodiodes 14 microns apart. This apparatus was used to examine the sodium and mercury doublets as well as the mode structure of an underpowered diode laser. Data for the study of the diode laser may be found here. More information on this may be found on Doug Broege's site in the entries for June, 2002. The rest of the REU students and I took a tour of the Van De Graaff and LINAC facilities here at Stony Brook as well this week.

### July 3rd, 2002

A short week this week due to the holiday. We gave a tour of our lab on Tuesday to the other REU students, and have been attending talks given by Dr. Hal Metcalf on the subject of Quantum Mechanics. Kelly Krieble at Moravian College has sent some of his data on the flicker of underpowered lasers. I've spent some time looking this over and I hope to be able to get similar data once a data acquisition system is chosen. As of yet, I am still trying to determine what system I should use for this purpose.

### July 12th, 2002

It's been decided that to take data I should use a computer's parallel port. I'm not going to actually worry about the real times between peaks, but rather use an arbitrary time from the computer and simply compare the times to each other.

### July 24th, 2002

The parallel port is able to detect a signal produced by a function generator equipped with a TTL out port, and the programs that I've written are able to detect and manipulate information received from the port. Unfortunately the photodetector which receives the signal from the laser isn't triggering the pulse generator as expected. It looks as though I'm not going to have enough time to figure out how to fix this though, as today is the last work day of the REU. I've been working on my abstract, report, and presentation this week. The presentation will be given tomorrow and then I'm going to go back to Missouri.

Home: http://laser.physics.sunysb.edu/~brendan/index.html