Using a transient-grating diffraction technique, we have compared the ultrafast dynamics of the linear reflectivity from a GaAs surface at the fundamental and second-harmonic frequencies with the dynamics of the second-harmonic generation (SHG) in refiection at an excitation level exceeding the melting threshold. It is shown that the ultrafast (within 100 fs) drop in the SHG efficiency cannot be accounted for by changes in the linear dielectric susceptibility that take place on a longer time scale. This fact indicates a fast change of the long-range crystalline symmetry of GaAs within a semiconductorlike phase, preceding a transition to the metallic phase as the crystal is melted.

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Watt-level yellow emitting lasers are interesting for medical applications, due to their high hemoglobin absorption, and for efficient detection of certain fluorophores. In this paper, we demonstrate a compact and robust diode-based laser system in the yellow spectral range. The system generates 1.9 W of single-frequency light at 562.4 nm by cascaded single-pass frequency doubling of the 1124.8 nm emission from a distributed Bragg reflector (DBR) tapered laser diode. The absence of a free-space cavity makes the system stable over a base-plate temperature range of 30 K. At the same time, the use of a laser diode enables the modulation of the pump wavelength by controlling the drive current. This is utilized to achieve a power modulation depth above 90% for the second harmonic light, with a rise time below 40  μs.

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We report on a cavity-dumped Yb:YAG thin disk laser with intracavity-frequency doubling to provide pulses in the millijoule energy range at a repetition rate of up to 100 kHz. The maximum average output power at 515 nm was 102 W with pulses of a pulse length of 300 ns. An additional advantage of the presented laser setup is the wide tunability of the pulse duration.