A passively mode-locked optically pumped semiconductor vertical-external-cavity surface-emitting laser (OPS-EXSEL) is disclosed. The laser is mode locked by a semiconductor saturable absorber mirror (SESAM) which forms part of an external cavity. Both the beam-quality limitations of edge-emitting lasers, and the power restrictions of electrically pumped surface-emitting lasers are overcome. The laser uses a semiconductor wafer in which a stack of quantum wells is grown adjacent to a single Bragg-mirror structure. Light from one or more multi-mode high-power diode lasers is focused onto the face of the wafer and pumps the wells by absorption in the barrier regions. The area of the laser mode on the active mirror can be about 104 times larger than the mode area on the facet of an edge-emitting laser, offering scope for the generation of high average power and large pulse energy. At the same time the external cavity enforces fundamental mode operation in a circular, near-diffraction-limited beam. With the laser, sub-picosecond pulse durations are achievable by eliminating coupled cavity effects and by external pulse compression. Band-gap engineering can be used to shape the pulses, or even integrate gain and saturable absorption within the same wafer. Thus, rugged, efficient pulsed laser sources with high average power in a nearly diffraction-limited beam, sub-picosecond pulse durations and multi-GHz repetition rates, which operate in a broad range of wavelengths accessible by bandgap engineering are made possible.
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