High-brightness semiconductor laser sources for materials processing: Stacking, beam shaping, and bars

A compact, reliable semiconductor laser source for materials processing, medical, and pumping applications is described. This industrial laser source relies on a combination of technologies that have matured in recent years. In particular, effective means of stacking and imaging monolithic semiconductor laser arrays (a.k.a., bars), together with advances in the design and manufacture of the bars, have enabled the production of robust sources at market-competitive costs. Semiconductor lasers are presently the only lasers known that combine an efficiency of about 50% with compact size and high reliability. Currently the maximum demonstrated output power of a 10-mm-wide semiconductor laser bar exceeds the 260 W level when assembled on an actively cooled heat sink. (The rated power is in the range of 50-100 W.) Power levels in the kilowatt range can be reached by stacking such devices. The requirements on the stacking technique and the optic assembly to achieve high brightness are discussed. Optics for beam collimation in fast and slow axis are compared. An example for an optical setup to use in materials processing will be shown. Spot sizes as low as 0.4 mm x 1.2 mm at a numerical aperture of 0.3 and output power of 1 kW are demonstrated. This results in a power density of more than 200 kW/cm(2). A setup for further increase in brightness by wavelength and polarization coupling will be outlined. For incoherent coupling of multiple beams into a single core optical fiber, a sophisticated beam-shaping device is needed to homogenize the beam quality of stacked semiconductor lasers. Applications economics dictate that reliable operation is achievable at numerous wavelengths (both for wavelength-specific applications and for brightness scaling through geometric wavelength multiplexing) and at ever higher per bar power levels. New material systems and epitaxial structures continue to be evaluated in this pursuit. Here we include details of designs and performance for devices operating at 808, 830, and 915 nm. These include characteristics of both single-emitter devices and bars.