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The lineshape of the I2P1/2→2P3/2 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 I2P1/2→2P3/2 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 I2P1/2→2P3/2 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.
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