Laser light backscattering off an electron beam-plasma system

The case of stimulated backscattering Raman instability that is combined with a two-stream Buneman instability has been analyzed. This problem bears on fabricating a rapidly tunable free electron laser (FEL) for IR countermeasures in the m wavelength range. The analysis is based on a weakly nonlinear theory and assumed a cold nonrelativistic electron beam and an equilibrium plasma to be described with a two-fluid model. The physical mechanism is based on the coherent bunching of the beam-plasma system due to the nonlinear ponderomotive force and the slow beam wave having negative energy. This paper analyzes a novel scattering configuration in which the IR (CO2) laser at 10.6 μm collides head-on against a nonrelativistic -beam firing through a puff of laser produced plasma of cm^-3, which has been previously produced by the CO2laser itself (e.g., producing the critical density 10¹⁹cm^-3and the reduced quiver velocity at pulsed 10¹⁴-10¹²W/cm²) and becomes underdense subsequently. The upshifted radiation is tunable at an aribtrary Ω1determined by the Doppler frequency relationship , where Ω0is the IR pump frequency and (≈0.14 for the 8 μm wavelength) is the -beam parameter of 5.11 keV and A/cm²such that . The synergic backscattering growth rate is the sum of both instabilities, e.g., , and may be referred to as the plasmon avalanche instability. Assuming the wide-interval-pulsed (WIP) -beam can be piecewisely flushed outside the interaction chamber after streaming through a laser produced plasma on each pass, then a useful free electron laser operation will result. Such a device is appropriately called the quasi-free electron laser (QFEL). The effect of axial magnetic field within the interaction chamber has also been include- d in the analysis. The advantages of QFEL result from 1) efficient use of the nonrelativistic -beam generation and two-stream bunching, 2) use of proven CO2 laser technology, and 3) its rapid tunability.