High power, high beam quality miniaturized diode laser module for direct material processing around 980 nm

摘要

In material processing applications laser diodes are commonly used for pumping of solid-state lasers, providing high efficiencies at demanding optical output powers. Limited by relatively low beam qualities in the high power scheme, their usage in direct material processing applications is still marginal. To achieve power levels in the 30 W class, so far the combined radiation of multiple broad area emitters has been necessary. However their output beam quality is far from diffraction limitation and correlated to the aperture width of the emitting laser diode. This work presents a novel miniaturized diode laser module, with an optical output power of more than 30 W in continuous wave operation (cw). Simultaneously the output beam is close to the diffraction limit with a beam propagation factor of M~2 < 3. The laser module layout is based on tapered diode lasers featuring wavelength stabilization by a monolithic distributed Bragg-grating. The tapered diode laser sources achieve an output power in the order of 8 W (cw) at a wavelength around 980 nm. To enhance the output power while maintaining the beam quality of the single emitters, six laser beams were combined by the use of polarization and wavelength coupling. The use of custom designed beam couplers is necessary to combine the given radiation intensities. Therefore a thin film polarizer was adapted to the output wavelength and intensity. Wavelength multiplexing is realized by the use of steep edge niters. By changing the angle of incidence the edge position can be tuned which enables multiple combination steps. All optical components were housed inside of a module with a footprint of 58 × 34 mm~2 only. The resulting high power and beam quality delivered by the module enables direct material processing.