Excimer lasers using molecular halogenides of rare gases RX (R = Ar, Kr, Xe; X = F, Cl, Br), excited by electron beams and in a gas discharge, are powerful sources of laser UV radiation [155, 156]. To pump these lasers, the radiation of nuclear explosions was also used (see Chap. 12). Excimer lasers operate most effectively in pulsed mode at high specific pumping powers of q > 0.1 MW/cm3, which is explained by the great radiation line width.

Excimer lasers can operate in quasi-CW mode, because after photon radiating, excimer molecules fall into the lower repulsive or weakly bound state. In this connection, some studies were carried out on the possibility of pumping excimer laser media with nuclear radiation using pulsed reactors as the neutron sources.

The largest number of investigations were devoted to the XeF-laser (A = 351 and 353 nm), which has the lowest laser threshold [60, 157—162]. In experiments [157] with the TRIGA reactor, a small-signal gain was registered of ~10-4 cm-1 at line 351 nm of the XeF molecule at a low specific power deposition of q « 40 W/cm3. Experiments performed with the SPR-III reactor showed that for the mixture 3He — Xe-NF3, the gain at the 351-nm line is around 7 x 10-3 cm-1 (q«5 kW/cm3) [158], while for pumping the mixture Ne(Ar)-Xe-NF3 with uranium fission frag­ments, a gain of ~2 x 10-3 cm-1 (q « 2 kW/cm3) was registered [48, 159]. Exper­iments using pulsed reactors with active media based on the molecule XeF [48,160] and KrF (A = 248 nm) [60], aimed at obtaining lasing, yielded no positive results. These experiments used the mixtures 3He-Xe-NF3, Ne-Xe-NF3 [48], Ne(Ar)-Xe — NF3(SF6) [160], and 3He-Kr-NF3 [60].

Calculations showed that for the mixture Ne-Xe-NF3, it is possible to obtain Пі ~ 1 % for q ~ 100 W/cm3 [161], and 500 W/cm3 [162]. The possibility of creating a nuclear-pumped XeF laser is determined primarily by the absorption coefficient in the active medium, the uncertainty of which greatly influences the results of calculations [161].

In conclusion, we note that study [163] reports achieving laser action at the transition of the XeCl molecule (A = 308 nm) when pumping the mixture Ar-Xe — CCl4(HCl) with uranium fission fragments in experiments with the EBR-L reactor (q ~1 kW/cm3). Although the authors assert that lasing was observed in the experiments, the cited data were insufficient for this conclusion.