Dynamics of an Underpowered Helium-Neon Laser. B. Wyker, University of Missouri; J. Noé, Laser Teaching Center, Department of Physics and Astronomy, Stony Brook University.

The operating behavior of an underpowered helium-neon (HeNe) laser was studied to determine whether there may or may not exist a chaotic aspect to the phenomena. Chaotic behavior in lasers has been noted in numerous systems such as those with modulated or conjugated feedback and in lasers with nonlinear open cavity resonators. The study was motivated by concepts outlined by researchers at Moravian College [1] regarding the observation of seemingly aperiodic behavior in underpowered gas lasers. A HeNe laser usually operates in a continuous manner, but when the voltage and current supplied to the gas-discharge tube is limited the continuous operation ceases. For certain values of current and voltage the laser goes into a flickering state. Observed pulsewidths ranged from around a quarter to a half of a millisecond while the pulse spacing ranged from around ten to twenty milliseconds. An apparatus was developed to collect data that could be used in a time series analysis to determine whether there indeed exists chaotic behavior. The relevant data was the time at which each of the pulses took place. This allowed for the comparison of the duration between pulses corresponding to each pulse. This data was taken through the use of a PC parallel port that monitored a function generator which was triggered by a photodetector. A HeNe laser, which was controlled by a variable DC power supply, was observed by the photodetector. Programs written in C++ were used to monitor the parallel port status and collect and manipulate the data into a set of times between pulses. It was intended that our observations would be compared with those of researcher's at Moravian College. Currently there are obstacles in completing the analysis due to problems in triggering the pulse generator and developing a program that regulates the length of time between the iterates which query the status of the parallel port. Further studies should take the Fourier transform of the pulse spacing values in order to find a primary frequency to be used in the production of a Poincaré section. This may then be utilized to determine whether there exists an attractor of extended structure, which would be necessary for there to be chaos. This study was supported by NSF Grant No. Phy 99-12312.

[1]  See http://home.moravian.edu/public/phys/research/research.html (bottom of page)

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