Method and apparatus for generating electromagnetic energy by creating a population inversion between upper and lower energy levels in a target substance. The population inversion is maintained by exciting the individual particles to a short lived resonant negative ion-like state and then to a particular neutral state at a rate greater than the total rate of decay from the resonant negative ion-like state to the various lower energy levels. Particles in the resonant negative ion-like state decay quickly to at least two energy states at differential rates, with decay to the upper energy state occurring at a rate sufficiently greater than decay to the lower energy state to ensure population inversion. Atoms or molecules in the upper state decay to the lower state, emitting coherent radiation of a predetermined frequency and wave length. Excitation of the particles to the short lived resonant negative ion-like state is produced by irradiating the target substance with a beam of electrons having an energy distribution centered about a resonant energy at which the individual particles respond, the energy distribution having a width of about 0.25 to about 5.0 eV. The power output may be varied by varying the current density of the electron beam, and the energy output may be either continuous or pulsed by controlling the application of the incident electron beam in a corresponding fashion.
An apparatus and method is described for greatly enhancing the power output f a free electron laser. To enhance the electron kinetic energy that is converted to laser radiation, the wave amplification resonance condition is continuously changed along the length of the laser interaction region. The changing resonance condition is achieved by use of a static magnetic field transverse to the injected electron beam, the magnetic field having a longitudinal magnetic field gradient.
A preconditioning beam is used to excite gas particles preferentially along a channel between two electrodes in a laser chamber. The preconditioning beam may be an electron beam or a laser beam. An electrical discharge between the electrodes is conducted along the channel by the excited gas particles to form a gas embedded plasma pinch. Depending on the profile of the discharge, the pinch may be stable or collapsing. The pinch emits vacuum ultraviolet radiation which photodissociates molecules of the photolytic laser medium confined by the chamber. The dissociation creates a population inversion, initiating lasing activity. A resonator system reflects the developing laser pulse back and forth through the chamber to stimulate further emissions and facilitate pulse amplification. The developed pulse is transmitted by appropriate means.
