Irradiation nonuniformity due to imperfections of laser beams

Intractable low-mode nonuniformities caused by power imbalance or pointing error of beams are studied quasi-analytically based on Skupsky’s axially symmetric model [S. Skupsky and K. Lee, J. Appl. Phys. 54, 3662 (1983)]. These nonuniformities can be improved by decreasing the imperfections σPΩ, or by increasing the number of laser beams NB: deteriorated irradiation uniformity is shown to be proportional to σPΩ/√NB. Criteria of these imperfections for high irradiation uniformity [≤1% root-mean square (rms)] are then presented in terms of NB. The model is further extended to treat general asymmetric beam patterns. Optimization of beam pattern is also a central issue.