The features of experiments using nuclear explosive devices which relate to the destruction of the laser device require careful preparation, in particular, of a detailed simulation of the physical processes in the active laser media and prelim­inary calculation of laser characteristics. These calculations were performed for lasers based on the transitions of the excimer molecules: XeF [23] and KrF [25].

Calculations [23] of experimental conditions [21—23] used a kinetic model of the XeF laser, which determined the laser characteristics on two spectral lines: 351 and 353 nm. Resulting from the solution of the radiative transfer equation, the total power density on each line was determined as a function of the distance to the coupling aperture at the top of the cone (Fig. 12.7). The radiation power at the surface of the focusing mirror was InR2 = 7.2 x 1010 W (R = 40 cm). This is approximately two times less than the power obtained experimentally. The calcu­lated maximum efficiency of the amplifier (2 %) was also lower than the experi­mental value (3 %).

A paper [25] analyzed the functioning of a laser device consisting of a cylindri­cal former and a conical amplifier with y-ray, travelling-wave pumping. A gas medium based on KrF (A = 249 nm) excimer molecules was considered as the active media. Special attention was paid to an analysis of the conditions for forming the directed radiation. Calculations showed that the efficiency of energy extraction from the conical amplifier as a function of its height was 20-50 %; the beam divergence at the output of the cone was 0«d0/L = 10~4 rad (where d0 is the diameter of the coupling aperture, and L is the length of the cone). These

Fig. 12.7 Dependence of the total power density of the 351 and 352 nm lines on the distance to the coupling aperture. The initial power densities at the input of the conic amplifiers were 1, 102, 104, and 106 W/cm2 (from bottom to top) [23]

calculations also showed that amplification of the spontaneous emission may influence the directivity of the useful radiation from the cone if the intensity of the spontaneous noise near the top of the cone is comparable to the saturation intensity of the active medium.