We report on optically-pumped vertical-external-cavity surface-emitting lasers passively mode-locked with a semiconductor saturable-absorber mirror. The potential of harmonic mode-locking in producing pulse trains at multigigahertz repetition rates has been explored. The results present first systematic study of multiple pulse formation in passively mode-locked VECSELs.

We present optically pumped semiconductor disk lasers with a thin dielectric layer placed between the semiconductor distributed Bragg reflector and the metallization interface. The approach is shown to enhance the reflectivity of the semiconductor mirror while introducing a negligible penalty to the thermal resistance of the device. The design has potential for improving the performance of semiconductor disk lasers by avoiding highly pump-absorbing metal layers and allowing thinner mirror structures. The advantages are expected to be especially prominent for material systems that employ thick thermally insulating semiconductor mirrors.

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Passive harmonic modelocking in a flip-chip semiconductor disc laser at a 193 GHz repetition rate with 900 mW of output power and a pulse duration of 830 fs is demonstrated. The high harmonic frequency is obtained via coupling of the laser cavity to an intracavity diamond heat spreader bonded to a semiconductor saturable absorber mirror.Introduction: Ultra-short pulse trains with repetition rates in the gigahertz range are of interest for numerous applications including optical clocking, arbitrary waveform generation, rapid terahertz time-domain spectroscopy and high-speed data transfer [1][2][3]. Semiconductor disc lasers (SDLs) combine high average output power and excellent beam quality owing to the thin disc geometry with the wavelength versatility natural to a semiconductor gain medium [4]. Recently, repetition rates above 100 GHz have been reported from semiconductor disc lasers modelocked by a semiconductor saturable absorber mirror (SESAM) [5]. In the referenced study, modelocking at a high harmonic of the fundamental cavity repetition rate was obtained by coupling the laser cavity to an intracavity etalon formed by a diamond heat spreader, which was capillary bonded onto the surface of the SDL gain element for cooling purposes. However, in the 1 mm wavelength range, higher output powers can be expected when using a so-called flip-chip cooling approach, in which the substrate is removed and the heat spreader is bonded underneath the gain mirror [6]. Thermal damage of the SESAM may impose further limitations to the power scaling of modelocked SDLs operating in the multi-GHz regime [7]. Strong local heating of the SESAM occurs because tight focusing of the laser mode at the SESAM is required for saturation of the absorber at the high repetition rate which is accompanied by a considerable decrease in pulse energy. In this Letter, we present a SESAM-modelocked flipchip SDL emitting at 1 mm with an average output power of 900 mW, a pulse repetition rate of 193 GHz and a pulse duration of 830 fs. A chemical vapour deposited (CVD) diamond heat spreader was attached to the SESAM to provide necessary heat removal at the high power level and to stabilise modelocking at the 150th harmonic of the cavity frequency.

We report on power scaling of optically-pumped semiconductor disk lasers using multiple gain scheme. The method allows for significant power improvement while preserving good beam quality. Total power of over 8 W was achieved in dual-gain configuration, while one-gain lasers could produce separately about 4 W, limited by the thermal rollover of the output characteristics. The results show that reduced thermal load to a gain element in a dual-gain cavity allows extending the range of usable pump powers boosting the laser output.