Alexandre Laurain

15 W Single Frequency Optically Pumped Semiconductor Laser With Sub-Megahertz Linewidth

We report on a single frequency optically pumped semiconductor laser exhibiting an output power of 15 W in continuous wave operation. The GaAs-based structure presents an emission wavelength of 1020 nm and a tuning range , with a continuous tunability of 9 GHz. The TEM00 output beam exhibits very low transverse phase fluctuations across the entire mode, leading to a beam quality . A free-running laser linewidth of 21 kHz has been deduced from frequency noise measurements for a sampling time of 1 ms and increases to 995 kHz for a sampling time of 1 s.

Design and Fabrication of Hybrid Metal Semiconductor Mirror for High-Power VECSEL

The design, fabrication, and characterization of a hybrid metal-semiconductor distributed Bragg reflector (DBR) for optically pumped vertical external cavity surface emitting laser are reported. The realization of a pure gold reflector attached to an AlGaAs/AlAs DBR is achieved through the realization of a lithography pattern alternating gold and titanium areas for better surface adhesion. This reduces from 28 to 14, and the number of DBR pairs is needed to achieve a reflectivity above 99.9%. Experimental results are supported by simulations and show an output power beyond 4 W with an optical efficiency of 19% and very low thermal impedance, validating the excellent reflectivity and bonding quality of the device.

2.7-

We present the design, technology, and performances of a tunable Sb-based diode-pumped type-I quantum-well (QW) vertical-external-cavity surface-emitting lasers emitting at 2.7 μm. The half vertical-cavity surface-emitting laser (VCSEL) structure was grown by molecular beam epitaxy with quantum-well growth temperature of 440 °C. The sample was thermally annealed to optimize the QW gain design. We report on room-temperature continuous-wave laser with 0.17-mW output power and low threshold incident pump intensity of 0.7 kW/cm2 while pumping at 830 nm with a commercial diode laser. The external cavity provides a circular TEM00 beam with a low divergence of 3.6°. The short mm-long optical cavity laser exhibits tunable single frequency operation, with a sidemode suppression ratio >;>; 23dB, a linewidth <;<;4;GHz, and a linear light polarization. Thermal and optical properties are studied.

\mu{\rm m}

High-power semiconductor disk lasers producing short pulses at high repetition rates are attractive for numerous applications. The peak power achievable is often limited by the stability of the mode-locked regime as harmonic mode locking or nonstationary pulsed operation emerges at high pump powers. In this Letter, we present a new passive and robust mode-locking scheme for a vertical-external-cavity surface-emitting laser (VECSEL). We placed the semiconductor gain medium and the semiconductor saturable absorber mirror (SESAM) strategically in a ring cavity to provide stable colliding pulse operation. With this cavity geometry, the two counterpropagating pulses synchronize on the SESAM, saturating the absorber together, which minimizes the energy lost and creates a transient carrier grating due to the interference of the two beams. The interaction of the two counterpropagating pulses is shown to extend the range of the mode-locking regime and to enable higher output power when compared to the conventional VECSEL cavity geometry. In this configuration, we demonstrate a pulse duration of 195 fs with an average power of 225 mW per output beam at a repetition rate of 2.2 GHz, giving a peak power of 460 W per beam, establishing a new (to our knowledge) state of the art in term of pulse duration and peak power combination. The remarkable robustness of the mode-locking regime is discussed and a rigorous pulse characterization presented.

Single-Frequency

Experimental and theoretical results on the mode-locking dynamics in vertical-external-cavity surface-emitting lasers with semiconductor and graphene saturable absorber mirrors are reviewed with an emphasis on the role of nonequilibrium carrier effects. The systems are studied theoretically using a fully microscopic many-body model for the carrier distributions and polarizations, coupled to Maxwells equations for the field propagation. Pump-probe measurements are performed with (sub-) 100 fs resolution. The analysis shows that the non-equilibrium carrier dynamics in the gain quantum-wells and saturable absorber medium significantly influences the systems response and the resulting mode-locked pulses. The microscopic model is used to study the pulse build up from spontaneous emission noise and to determine the dependence of achievable pulse lengths and fluences on the amounts of saturable and non-saturable losses and the optical gain. The change of the group delay dispersion (GDD) on the pump level is examined and the dependence of the pulse lengths on the total amount of GDD is demonstrated experimentally. Theory-experiment comparisons are used to demonstrate the highly quantitative accuracy of the fully microscopic modeling.

{\rm TEM}_{00}

We demonstrate a continuous wave, single frequency terahertz (THz) source based on parametric difference frequency generation within a nonlinear crystal located in an optical enhancement cavity. Two single-frequency VECSELs with emission wavelengths spaced by 6.8 nm are phase locked to the external cavity and are used as pump sources for the nonlinear down conversion. The emitting THz radiation is centered at 1.9 THz and has a linewidth of less than 100 kHz. The output power of the source exceeds 100 μW. We show that the THz source can be used as local oscillator to drive a receiver used in astronomy applications.

Low-Threshold Sb-Based Diode-Pumped External-Cavity VCSEL

We present an in-depth analysis of the VeCSELs frequency and the intensity noise.

Colliding pulse mode locking of vertical-external-cavity surface-emitting laser

We present a novel cavity design for vertical external cavity surface emitting lasers (VECSELs) enabling multiple interactions with the gain structure under different angles in a single round trip. This allows for a low round-trip group delay dispersion (GDD) despite using high-gain resonant VECSEL structures possessing pronounced resonances in their reflective GDD profile. Femtosecond-regime pulses with an average output power of 1.14 W and record peak intensities for mode-locked VECSELs of 6.3 kW are presented with simulations demonstrating the GDD compensating mechanism employed in this scheme.

Ultrafast non-equilibrium carrier dynamics in semiconductor laser mode-locking

We investigate experimentally and theoretically the influence of non-radiative carrier losses on the performance of VECSELs under pulsed and CW pumping conditions. These losses are detrimental to the VECSEL performance not only because they reduce the pump-power to output-power conversion efficiency and lead to increased thresholds, but also because they are strong sources of heat. This heating reduces the achievable output power and eventually leads to shut-off due to thermal roll-over. We investigate the two main sources of non-radiative losses, defect recombination and Auger losses in InGaAs-based VECSELs for the 1010nm-1040nm range as well as for InGaSb-based devices for operation around 2μm. While defect related losses are found to be rather insignificant in InGaAs-based devices, they can be severe enough to prevent CW operation for the InGaSb-based structures. Auger losses are shown to be very significant for both wavelengths regimes and it is discussed how structural modifications can suppress them. For pulsed operation record output powers are demonstrated and the influence of the pulse duration and shape is studied.

Terahertz generation by difference frequency conversion of two single-frequency VECSELs in an external resonance cavity

We report room-temperature high-peak-power operation of an optically pumped semiconductor laser based on the InGaAs/GaAs material system. We present the design of the semiconductor structure and optimization strategies to extract the maximum pulsed peak power. The gain structure was pumped by a 775-nm Alexandrite laser with a pulsewidth adjustable from 400 ns to 1 μs and a repetition rate of 3 Hz. A new record peak power of 400 W at a wavelength of 1020 nm was obtained with a Gaussian-shaped submicrosecond pulse. An optical-to-optical efficiency of 28% is demonstrated at maximum power. The key parameters limiting the output power are discussed.