The dependence of the beam quality of tapered laser oscillators and amplifiers on the modal optical gain is demonstrated experimentally and theoretically for the first time. Tapered devices with high-(HMG) and low-modal gain (LMG) structures are compared in terms of output power and beam quality. At high-output powers the beam quality of LMG devices is by a factor of ten better than the beam quality of high-modal gain devices. The beam quality remains nearly unchanged up to power levels of more than 2-W continuous-wave (CW) where a beam quality factor of M(2)< 3 is achieved for both, tapered laser oscillators and tapered amplifiers

A tunable external cavity semiconductor laser with > 1 W CW near-diffraction-limited output power between 1030 and 1085 nm is demonstrated. A tapered power amplifier with novel epilayer structure is used as the gain element. Near the gain peak at 1055 nm an output power of 1.6W CW is obtained

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A comprehensive model has been developed to study the operating characteristics of high-power high-brightness lasers consisting of a ridge-waveguide section coupled to a tapered region. The model, based on the Beam Propagation Method (BPM), includes a non-linear gain coefficient, current spreading due to junction voltage, and thermal effects taking into account for the first time to our knowledge a longitudinal gradient in the device temperature. We first demonstrate that during operation unwanted radiation that does not couple into the lateral mode of the waveguide, systematically propagates into the tapered region, and leads to the deterioration of the beam quality. To deflect and scatter this radiation, the use of specific cavity-spoiling elements, consisting of grooves etched down through the active region, appears necessary. We also study the role of the ridge section length in the operation of the device. A long ridge-waveguide region, providing both a well defined fundamental mode in the ridge-waveguide, and a gain saturation in the tapered region, improves the beam stability, but can lead, on the other hand, to optical self-focusing. Thermal effects are also investigated. We show how thermal lensing induces a lateral quadratic phase curvature and therefore alters the astigmatism of the device.