Diffractive focusing of an input pulse and giant energy gain in a laser based on an auto-wave photon-branched network

The wave approximation is used to analyse the energy parameters and the spatiotemporal behaviour of the electromagnetic field in a pulsed chemical laser based on a photon-branched chain reaction in an unstable telescopic cavity with an input coupling aperture through which the reaction is initiated by IR radiation in a gaseous disperse medium composed of H₂ , F₂ , O₂ , He, and Al particles. It is shown that diffractive multifocal focusing of a plane input wave, ensuring minimisation of the initially excited volume and a correspondingly strong reduction (down to microjoules) of the required input pulse energy, occurs in the range of small input aperture diameters d₀ = (3 — 30)λ. A giant energy gain of ~3×10⁹ can be reached as a result of this optical effect and also because of auto-wave propagation of a photon-branched chain reaction throughout the whole volume of the laser. This giant gain makes it possible to construct a self-contained laser with a kilojoule output energy, which can be initiated by microjoule input pulses.