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 &sgr;P&OHgr;, or by increasing the number of laser beamsNB: deteriorated irradiation uniformity is shown to be proportional to &sgr;P&OHgr;/&sqrt;NB. Criteria of these imperfections for high irradiation uniformity [≤1% root‐mean square (rms)] are then presented in terms ofNB. The model is further extended to treat general asymmetric beam patterns. Optimization of beam pattern is also a central issue.