Hydrogen Fluoride vs Deuterium Fluoride Space-Based Laser Performance Comparison

Abstract

The on-orbit performances of hydrogen fluoride (HF) and deuterium fluoride (DF) lasers are compared. Only free-space propagation, without any atmospheric effects, has been considered in comparing the lethality, or brightness, of the two systems. An arbitrarily chosen set of residual values of wave front error, including both high and low spatial frequencies, and jitter are employed as degradation terms in calculating the brightness. Whereas conventional thinking is that shorter wavelengths are always better, this is not always the case when degradation terms are introduced. It is shown that the brightness of a DF laser beam is not reduced by the canonical factor of 2 from HF, i.e., by the ratio of wavelengths squared, as calculated without the effects of wave front error and jitter, but that it is equal to or greater than that of an HF laser (at equal power and primary mirror diameter) for the chosen set of degradation terms. Atmospheric propagation is presented as a separate issue, completely independent of the brightness, to show the greatly extended flexibility and lethality of DF over HF when engaging a target in the Earth's atmosphere. Also, the nozzle performance of HF and DF lasers are about equal and so their on-orbit volumes are equal and their weights are comparable, although the mode width of DF is about twice as long as that of HF, which reduces the intensity on the resonator optics by a factor of two and reduces the internal diffractive losses by about 30%.