Multiwatt–power highly–coherent compact single–frequency tunable Vertical–External–Cavity–Surface–Emitting–Semiconductor–Laser

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We demonstrate high power (2.1W) low noise single frequency operation of a tunable compact verical-external-cavity surface-emitting- laser exhibiting a high beam quality. We took advantage of thermal lens-based stability to develop a short (3-10 mm) plano-plano external cavity without any intracavity filter. The semiconductor structure emitting at 1microm is optically pumped by a 8W commercial 808 nm multimode diode laser at large incidence angle. For heat management purpose the GaAs-based VECSEL membrane was bonded on a SiC substrate. We measured a low divergence quasi-circular TEM00 beam (M2 = 1.2) close to diffraction limit, with a linear light polarization (>30 dB).We simulated the steady state laser beam of this unstable cavity using Fresnel diffraction. The side mode suppression ratio is > 45 dB. The free running laser linewidth is 37 kHz limited by pump induced thermal fluctuations. Thanks to this high-Q external cavity approach, the frequency noise is low and the dynamics is in the relaxation-oscillation-free regime, exhibiting low intensity noise (< 0.1%), with a cutoff frequency approximately 41MHz above which the shot noise level is reached. The key parameters limiting the laser power and coherence are studied. This design/properties can be extended to other wavelengths.