Cylindrical microlenses for collimating high-power diode lasers

Monolithic linear arrays of diode lasers, also known as diode laser bars, are the basic elements for most high-power laser applications such as solid-state laser pumping or material processing Cylindrical microlenses used as fast-axis collimators for 10-mm diode bars require very high angles of aperture (up to 100 degree FW1/e2, equivalent to a numerical aperture of approx. 0.8) to capture most of the emitted laser power. For the efficient longitudinal pumping of laser rods, or the narrow focusing of the diode laser radiation (fiber coupling, material processing), high-quality microlenses with small lens aberrations are necessary to avoid power losses and beam quality degradation. In this paper, lens design considerations are presented together with alignment tolerances and the variation of the collimated beam parameters. Measuring methods for the lens characterization are discussed. Manufacturing techniques are summarized, and the performance of microlenses is measured by the beam width and divergence of the collimated diode laser beam.