Inverse-bremsstrahlung absorption rate in an intense laser field

Inverse bremsstrahlung is one of the important mechanisms for heating plasmas with lasers. In the intense fields required for laser fusion, processes involving multiphoton effects are very important. This paper reviews and compares the different approaches used to quantify the effect of intense fields on the inverse-bremsstrahlung absorption rate. The quantum-mechanical treatment of this problem requires summation of the contribution of large numbers of photons. Numerical problems associated with this summation have made direct evaluation difficult. In this paper the authors describe a method, applicable to many potentials of interest, for transforming the sum over a large number of complicated terms into a rapidly converging sum. Numerical results for both classical and quantum treatments are presented and compared, and the errors introduced by several approximations are quantified