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Proceedings Paper

Prediction of I2P1/2-->2P3/2 transition lineshapes from 3-D, time dependent simulations of chemical oxygen-iodine laser (COIL) flowfields
Author(s): Timothy J. Madden
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Paper Abstract

The lineshape of the I2P1/22P3/2 transition provides a means to ascertain a variety of useful information regarding the performance of the chemical oxygen-iodine laser (COIL). The value at the center of the lineshape, commonly referred to as the 'line center,' is proportional to the laser amplification on the I2P1/22P3/2 transition. The infinite integral of the lineshape is proportional to the number density of the ground and excited states of atomic iodine in the gas, indicating the degree of I2 dissociation. And the width of the lineshape indicates the amount of broadening of the transition, both due to collisional and Doppler shift effects. As the Doppler shift is proportional to velocity, the width of the transition can be used to estimate the degree of random molecular motion in the gas, expressed in macroscopic terms as temperature. A Doppler shift to the frequencies in the transition can also occur through the straight-line, bulk motion of the gas, and this can be used to examine the velocity field of the gas. However, the flow may experience rotation through the presence of eddies carried within the gas, and these too may contribute to the Doppler shift of the lineshape frequencies. Given that eddies by virtue of their positive and negative velocity components can induce positive and negative Doppler shift, the widening of the lineshape is similar to thermal motion which also includes positive and negative velocities. Thus, when interpreting transition lineshapes, if some account is not made for both thermal and rotational motion, the effect of either physical process will be over-estimated. The work discussed here is oriented toward examining the interplay between the gas dynamics and the lineshape of the I2P1/22P3/2 transition, and in turn determine the ramifications for the use of spectroscopic lineshape based diagnostics and interpretation of their data. These efforts in turn are directly linked to efforts improve the understanding of the physical processes underlying chemical lasers, as excursions outside the traditional operational parameter space become increasingly necessary.

Paper Details

Date Published: 21 February 2008
PDF: 12 pages
Proc. SPIE 6874, High Energy/Average Power Lasers and Intense Beam Applications II, 687407 (21 February 2008); doi: 10.1117/12.773776
Show Author Affiliations
Timothy J. Madden, Air Force Research Lab. (United States)


Published in SPIE Proceedings Vol. 6874:
High Energy/Average Power Lasers and Intense Beam Applications II
Steven J. Davis; Michael C. Heaven; J. Thomas Schriempf, Editor(s)

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