Abstract: A method for producing high optical power density. Laser beams emitted from a plurality of laser bars are combined by spatial multiplexing to become substantially parallel with an optical axis. Each single laser bar includes one or more diode lasers. The slow axes of adjacent diode lasers of the single laser bar are substantially parallel with each other and the adjacent diode lasers emitting substantially to the same direction. The laser bars are arranged in two or more sectors around the optical axis. The width of the effective light-emitting near-field of at least one of the laser bars is less than 2.5 millimeters in the direction of the slow axis of the diode lasers of the at least one laser bar.