BEAM QUALITY OF DIRECT NUCLEAR PUMPED LASER-AMPLIFIERS

The achievable beam quality resulting from heavy charged particle pumping of transverse flow, gas laser amplifiers is presented. The charged particles are generated by nuclear reactions in either B4C or UO2 coated on plates parallel to the lasant flow. The character of the laser medium aberration resulting from the nonuniform energy deposition and fluid dynamic effects is discussed as well as the effects on the far-field beam quality of the amplifier. Pumping from plates parallel to the flow produces a medium aberration which is dominated by a cylindrical focus perpendicular to the flow, and a tilt in the flow direction. Beam qualities of better than 2 times diffraction limited (TDL) are obtained with a B4C fueled 1-m-long amplifier pumped at an average power deposition of 100 W/cm3 with an inlet 0.1-MPa helium flow at 100 m/s. Amplifiers using UO2 fuel coatings to pump argon under the same flow conditions with fission fragments have similar qualitative laser medium aberrations but with larger magnitude, resulting in beam qualities of > 20 TDL for a 100 W/cm3 average power deposition.