Beam shaping of high power laser diode bars

Abstract

A technique for reshaping the highly astigmatic beam from a high-power laser diode bar by use of two parallel mirrors is studied theoretically and experimentally. It is found that the output from the 1 µm x 1 cm laser diode can be reshaped and focused down to a spot of <0.5 mm diameter with reasonably good beam symmetry +/- 5 mm from the focal plane. Experimentally, it was found that ~80% of the output power at the laser diode could be coupled into this spot. This is an efficient technique for laser-diode end-pumping of high-power solid-state lasers. Further, several diode parameters that affect the design of the beam shaping system are investigated, and two main operating regimes are identified. For diodes with a small number (~20) of active regions, a geometry where the diode bar is imaged onto the mirrors should be used, whereas for diodes with a large number (~50) of active regions, a nonimaging geometry can be used. The imaging geometry offers better output beam quality, while the non-imaging geometry offers greater flexibility and easier alignment.