Abstract
We investigate antireflection (AR) coating materials for two different operation lasing regimes requiring broad spectral bandwidth. We characterize high-power continuous-wave (CW) wavelength-tunable vertical-external-cavity surface-emitting semiconductor lasers and their passive mode-locking capabilities when using semiconductor saturable absorber mirrors. One laser gain design was investigated with different single dielectric layers as AR coatings. The dielectric coating materials used were SiO2, Al2O3, Ta2O5, and TiO2. The AR coating was designed to reduce pump reflection and increase the confinement factor of the microcavity. Average power of 4.6 W in CW and a total wavelength tuning range of 42 nm has been observed with the SiO2-coated structure. The shortest pulse of 708 fs was also observed for the SiO2-coated structure, with a corresponding CW wavelength tuning range of 36 nm.
Highlights
The broad intrinsic gain bandwidth of optically pumped surface-emitting semiconductor laser chips is of interest for ultrashort pulse generation, as well as for wavelength-tunable narrowband emission
Etalons have been primarily used in ML-vertical-external-cavity surface-emitting lasers (VECSELs), and they are preferable as they can be thinner than birefringent filters (BRFs)
Different innovative schemes have been investigated to increase the tunability range of VECSELs, a two-chip gain cavity in Ref. [8], quantum well (QW) thickness variation in the gain chip in Ref. [9], Fabry–Perot design with two resonant wavelengths [15], and parametric optimization of the layer thicknesses to produce a spectrally broadened confinement factor [16]. Another route to increasing tunability range involves membrane external cavity surface-emitting lasers (MECSELs) that do not have a distributed Bragg reflector (DBR), which results in a much-weakened microcavity effect [14]
Summary
The broad intrinsic gain bandwidth of optically pumped surface-emitting semiconductor laser chips is of interest for ultrashort pulse generation, as well as for wavelength-tunable narrowband emission. In passively mode-locked operation, vertical-external-cavity surface-emitting lasers (VECSELs) [1] incorporating semiconductor saturable absorber mirrors (SESAMs) [2] have achieved pulse durations down to 60 fs in trains of pulses and around 100 fs in single-pulse operation [3,4] with an average power of 100 mW. The disk laser geometry is suitable for high-power operation, with a current record of more than 100 W CW at 1 μm emitted by a single optically pumped InGaAs/GaAs quantum well gain chip on a diamond submount [5].
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