Maintenance of a Chapman Jouguet laser supported detonation (LSD) wave requires complete absorption of the laser beam in an absorption front travelling supersonically with respect to the upstream gas. A requirement for LSD maintenance is that this distance be less than the radius of the beam. A computational scheme was developed to study the structure of LSD waves in various gases. A simultaneous solution of the mass and momentum conservation equations yields a (Maxwell) line when p is plotted versus 1/&rgr;, the slope of which is related to the velocity of the wave. The physical distance x in the wave corresponding to each point on the Maxwell line is determined by calculating the inverse bremsstrahlung absorption coefficient k as a function of the p and &rgr; and then inverting the equation Iabs(p, &rgr;)=Io(1–exp–∫xk dx’) for x. The method is used to calculate wave thicknesses for a variety of gases (H2O, LiH) that are being considered as propellant materials for laser propulsion. Results are presented for a laser wavelength of 10.6 &mgr;m and upstream gas densities in the 10−3to 10−4g/cc range. The effect of adding a low ionization potential seed to the propellant is explicitly calculated.