Fig. 11. Free electron laser process: electron velocity in same direction as electric field of EM wave. The electron loses, and the wave gains, energy. 3.5 Chemical Laser Molecules of lasant excited to the upper level of the lasing transition are produced by chemical reaction. For example, in a hydrogen fluoride (HF) laser, where HF* denotes a hydrogen fluoride molecule excited to the upper level of a lasing transition and HF a molecule in the lower level of that transition. According to the third reaction, a photon of frequency v and energy he (h is Planck's constant) stimulates the HF* to emit a second photon of the same frequency, the HF* going to HF in the process. The radiation from an HF laser is in the 2.6-3.5 jim range. Chemical lasers consume a fuel and an oxidizer and produce one or more reaction products as exhaust. In the case of the HF laser, the fuel is H, the oxidizer is F, and the reaction product is HF. Chemical lasers are typically operated open-cycle and can function only until the fuel and oxidizer are consumed. However, open-cycle operation is not essential (19). A subsystem for reconstituting the fuel and oxidizer from the reaction products could be included in a chemical laser system to achieve closed-cycle operation. The HF laser would have the following reconstituting reaction: which could be accomplished by electrolysis or conceivably by direct sunlight (19).
RkJQdWJsaXNoZXIy MTU5NjU0Mg==