High-power Semiconductor Disk Lasers Research Articles

High-power 970 nm semiconductor disk laser.

Semiconductor disk lasers (SDLs) have emerged at the frontier of laser technologies. Here, the chip design, packaging process, resonator, pumping strategy, etc. are optimized for the performance improvement of a 970 nm SDL. After optimization, a power of 70.3 W is attained under continuous wave (CW) operation, and the corresponding thermal resistance is around 0.49 K/W. The laser is highly efficient with a maximum slope efficiency of 58.2% and the pump threshold is only around 1.83 kW/cm2. Furthermore, the emission performances under quasi-continuous wave (QCW) pumping are also explored. Setting the duty cycle to about 11%, the chips can output a peak power of 138 W without thermal rollover, and the single pulse energy can reach about 13.6 mJ. As far as we know, they are the best results in terms of power/energy in this wavelength SDL. These explorations may help to understand the thermal characteristics in high-power SDLs and may also be regarded as an extension and enrichment of the earlier works on this topic.

Near-diffraction-limited semiconductor disk lasers

High power semiconductor disk lasers (SDLs) with near-diffraction limited beam quality were demonstrated. The influence of the incident angle, operation temperature, cavity length and curvature radius of the output coupler mirror on the beam quality were investigated. The condition for near-diffraction limited beam quality was analyzed. Choosing the pump spot size 10%–20% smaller than the fundamental mode size is the roughly optimized condition for achieving near-diffraction limited beam quality in SDLs. Finally, the SDL with an output power of 12.9 W and M2<1.2 was realized.

High Power (&gt;27 W) Semiconductor Disk Laser Based on Pre-Metalized Diamond Heat-Spreader

High power semiconductor disk lasers (SDLs) were demonstrated based on the thermal management using pre-metalized diamond heat-spreader. The processing of pre-metallization using Cu-Sn alloy was developed. The resultant and influence of pre-metallization on the thermal performance of SDLs were investigated. It was found that the pre-metalized diamond heat-spreader was able to improve effectively not only the thermal resistance but also the bonding quality. 38% decrease on the thermal resistance of SDL was realized. The CW power exceeding 27 W, limited by the available pump power, was demonstrated.

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

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.

Graphene saturable absorber for high power semiconductor disk laser mode-locking

Here, we report on the development of an antiresonant graphene-based one-dimensional structure which allows the control of linear and nonlinear device performance through optical confinement. A record average output in excess of 10 W is achieved by integrating this antiresonant graphene saturable absorber mirror into a vertical-external-cavity-surface-emitting-laser at 1030 nm, which leads to strong evidence of mode-locking, generating pulses with energies up to 2.8 nJ and a pulsewidth of 353 fs.

High power semiconductor disk laser with a semiconductor-dielectric-metal compound mirror

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.

Pulse repetition rate scaling from 5 to 100 GHz with a high-power semiconductor disk laser

The high-power semiconductor laser studied here is a modelocked integrated external-cavity surface emitting laser (MIXSEL), which combines the gain of vertical-external-cavity surface-emitting lasers (VECSELs) with the saturable absorber of a semiconductor saturable absorber mirror (SESAM) in a single semiconductor layer stack. The MIXSEL concept allows for stable and self-starting fundamental passive modelocking in a simple straight cavity and the average power scaling is based on the semiconductor disk laser concept. Previously record-high average output power from an optically pumped MIXSEL was demonstrated, however the long pulse duration of 17 ps prevented higher pulse repetition rates and many interesting applications such as supercontinuum generation and broadband frequency comb generation. With a novel MIXSEL structure, the first femtosecond operation was then demonstrated just recently. Here we show that such a MIXSEL can also support pulse repetition rate scaling from ≈5 GHz to >100 GHz with excellent beam quality and high average output power, by mechanically changing the cavity length of the linear straight cavity and the output coupler. Up to a pulse repetition rate of 15 GHz we obtained average output power >1 W and pulse durations <4 ps. Furthermore we have been able to demonstrate the highest pulse repetition rate from any fundamentally modelocked semiconductor disk laser with 101.2 GHz at an average output power of 127 mW and a pulse duration of 570 fs.

Full characterization of a high-power semiconductor disk laser beam with simultaneous capture of optimally sized focus and farfield

We report on a beam characterization method that is based on the simultaneous measurement of the focus field and the farfield, thus avoiding problems with beam fluctuations during the measurement. By using reflections from both sides of a planoconvex lens, the method implements two branches of an optical system working simultaneously. Also, by letting the planoconvex lens be antireflection treated, and by allowing for both of the reflected fields to fill large and approximately equal areas on a camera detector array, the method significantly lowers the intensity onto the detector array, thus minimizing the need for additional disturbing attenuation filters to avoid camera saturation. In the numerical retrieval of the phase distribution, based on the measured intensity distributions of the focus and farfield, iterative propagation between the two branches is performed. The phase retrieval uses the two-step algorithm for the numerical field propagation conveniently providing an arbitrary choice of sampling distance in each plane.

Optimization of a Broadband Gain Element for a Widely Tunable High-Power Semiconductor Disk Laser

The layer structure of the gain element in an optically pumped semiconductor disk laser was parametrically optimized with respect to a target function specifying a desired unsaturated reflectance over a desired wavelength range at a constant pump intensity. Spectral threshold pump intensity measurements confirmed the efficacy of the design, showing a much wider low-threshold regime than a conventional nonbroadband gain element, in good agreement with simulations. This evaluation avoids the possible influence of additional factors under high-power operation. Nonetheless, having a high and nearly constant broadband unsaturated reflectance at low pump intensity is a key to obtain good high-power performance, as evidenced by the obtained continuous tuning from 967 to 1010 nm with a maximum output power of 2.6 W.

High-power semiconductor disk laser based on InAs∕GaAs submonolayer quantum dots

An optically pumped semiconductor disk laser using submonolayer quantum dots (SML QDs) as gain medium is demonstrated. High-power operation is achieved with stacked InAs∕GaAs SML QDs grown by metal-organic vapor-phase epitaxy. Each SML-QD layer is formed from tenfold alternate depositions of nominally 0.5 ML InAs and 2.3 ML GaAs. Resonant periodic gain from a 13-fold nonuniform stack design of SML QDs allows to produce 1.4W cw at 1034nm. The disk laser demonstrates the promising potential of SML-QD structures combining properties of QD and quantum-well gain media for high-power applications.