Membrane External-cavity Surface-emitting Laser Research Articles

Bi-frequency operation in a membrane external-cavity surface-emitting laser.

We report on the achievement of continuous wave bi-frequency operation in a membrane external-cavity surface-emitting laser (MECSEL), which is optically pumped with up to 4 W of 808 nm pump light. The presence of spatially specific loss of the intra-cavity high reflectivity mirror allows loss to be controlled on certain transverse cavity modes. The regions of spatially specific loss are defined through the removal of Bragg layers from the surface of the cavity high reflectivity mirror in the form of crosshair patterns with undamaged central regions, which are created using a laser ablation system incorporating a digital micromirror device (DMD). By aligning the laser cavity mode with the geometric centre of the loss patterns, the laser simultaneously operated on two Hermite-Gaussian spatial modes: the fundamental HG00 and the higher order HG11 mode. We demonstrate bi-frequency operation over a range of pump powers and sizes of spatial loss features, with a wavelength separation of approximately 5 nm centred at 1005 nm.

Effect of Non-Resonant Gain Structure Design in Membrane External-Cavity Surface-Emitting Lasers

The operation of a semiconductor membrane external-cavity surface-emitting laser (MECSEL) employing a gain membrane with a cavity design, which is non-resonant regarding the two semiconductor - heat-spreader interfaces, is presented. The MECSEL delivers watt-level output power, in line with state-of-the-art results. The study provides new evidence that the design criteria of a MECSEL gain region are significantly relaxed compared to active regions employing distributed Bragg reflectors, for which the field distribution is set by the Bragg condition leading to tight tolerances for positioning of the emitting quantum structures. The study has relevance especially for the development of mode-locked MECSELs by minimizing the impact of defective Fabry-Pérot micro-cavity effects due to reflections between the semiconductor gain structure and the two heat-spreader elements placed on each side of the semiconductor membrane.

In-Well Pumping of a Membrane External-Cavity Surface-Emitting Laser

We present a detailed characterization and comparative study of a membrane external-cavity surface-emitting laser (MECSEL) operating in the λ = 1125-1190 nm wavelength range under in-well pumping (at 1070 nm) and barrier-pumping (at 808 nm). The slope efficiency of the laser is significantly improved from 21% with barrier-pumping to 39% when pumping only the quantum wells at 1070 nm at a heat-sink temperature of 10 °C. To address the low pump absorbance with in-well pumping, we design and implement a low-aberration multi-pass pumping scheme. An optical output power of 28.5 W and slope efficiency of ∼28% is achieved with 8 circulating passes. This represents the highest output power demonstrated in any MECSEL, as well as the highest output power in-well pumped vertical external-cavity surface-emitting laser (VECSEL). It is noted that our reported output power is only limited by the available laser input power and no thermal roll-over is observed.

Quantum dot membrane external-cavity surface-emitting laser at 1.5 μm

A membrane external-cavity surface-emitting laser (MECSEL) with an InAs/InP quantum dot (QD) based gain region is demonstrated. The pumping scheme employs a 90° off-axis parabolic mirror to focus the diode laser pump beam to a nearly circular pump spot. With this pump arrangement, the QD MECSEL with SiC heat spreaders produced 320 mW output power at room temperature with direct emission in the near-infrared at 1.5 μm. We report a record value of 86 nm for the tuning range at this wavelength region, owing to a broad QD gain bandwidth and wide tunability in MECSELs.

Demonstration of a 20‐W membrane‐external‐cavity surface‐emitting laser for sodium guide star applications

We present a record 20-W continuous-wave output power membrane-external-cavity surface-emitting laser (MECSEL) double-bonded to silicon carbide (SiC) heat spreaders emitting around 1178 nm. We achieved a maximum slope efficiency of 27.7% and an optical-to-optical efficiency of 26.7%. By utilising an intracavity birefringent filtre, the wavelength was tuned over 75 nm and maximum output power of 12.7 W was recorded at 1178 nm. This study shows the potential of MECSELs to achieve high-performance and cost-effective optically pumped semiconductor disk lasers targeting applications in sodium guide stars.

Growth and characterization of InP-based 1750\xa0nm emitting membrane external-cavity surface-emitting laser

The epitaxial growth and emission properties of a membrane external-cavity surface-emitting laser (MECSEL) are demonstrated in the 1750 nm band. A heterostructure consisting of InGaAs quantum wells enclosed by InGaAlAs barriers was deposited on InP by molecular beam epitaxy. The emitted power exceeded 1.5 W, which is the highest that has been reported in this spectral range to date.

High-Power 1770 nm Emission of a Membrane External-Cavity Surface-Emitting Laser

An InGaAlAs/InP membrane external-cavity surface-emitting laser (MECSEL) operating at 1770 nm is reported for the first time. A record high power of 7.7 W is registered at -20°C. This is the record high emission power registered for any surface emitting InGaAlAs-based semiconductor laser at a wavelength longer than 1480 nm. A power value of 3.5 W is measured at 20 °C. The lasing is observed up to 60 °C. The high-power emission is achieved due to lateral and longitudinal power scaling realized by enlarging the pump spot diameter to $400~\mu \text{m}$ and the double-side pumping (DSP) of a single chip of extended thickness. We analyze the thermal properties and evaluate the temperature inside the laser membrane. We present the characteristic temperature (T0) as a function of temperature. The T0 is measured to be 70 K at -20°C and 26 K at 55 °C. Our data support the explanation that the increase in the maximum power of the DSP MECSEL originates from an improvement in the thermal properties rather than from more uniform carrier injection into the quantum wells.

Power scaling and thermal lensing in 825 nm emitting membrane external-cavity surface-emitting lasers

We present a membrane external-cavity surface-emitting laser (MECSEL) operating around 825 nm at room temperature. With a tuning range of 22 nm, the MECSEL fills the spectral gap between 810 nm and 830 nm, and extends the wavelength coverage of this category of high-beam-quality semiconductor lasers. For high-power operation, the pump spot size and cavity mode size can be enlarged in MECSELs. We apply this technique and demonstrate power scaling. The maximum output power is increased from 0.7 W to 1.4 W. Investigations on the beam quality reveal thermal lensing with a marginally changing M 2 value close to the diffraction limit.

Membrane external-cavity surface-emitting laser emitting at 1640 nm

We fabricated and characterized a membrane external-cavity surface-emitting laser (MECSEL) emitting at 1640 nm. This is the first, to the best of our knowledge, description of this type of laser emitting at the long-wavelength telecommunication band. Double-sided diamond heat spreaders were used to efficiently dissipate heat. Emission producing 1.2 W of power was demonstrated. We suggest that optimization of the laser has the potential to increase generated power.

Comparison of single-side and double-side pumping of membrane external-cavity surface-emitting lasers.

We studied and compared single-side pumping (SSP) and double-side pumping (DSP) of a semiconductor membrane external-cavity surface-emitting laser (MECSEL). The MECSEL-active region was based on an AlGaAs quantum well structure embedded between two silicon carbide (SiC) wafer pieces that were used as transparent intra-cavity (IC) heat spreaders creating a symmetrical cooling environment. The gain structure targeted emission at 780 nm, a wavelength region that is important for many applications, and where the development of high-brightness high-power laser sources is gaining more momentum. By DSP at 20°C heat sink temperature, we could reduce the laser threshold from 0.79 to 0.69 W of absorbed pump power, while the maximum output power was increased from 3.13 to 3.22 W. The differential efficiency was improved from 31.9% to 34.4%, which represents a record value for SiC-cooled vertically emitting semiconductor lasers. The improvements are enabled by a reduced thermal resistance of the gain element by 9% compared to SSP. The beam quality was measured to be M2<1.09. Finally, we demonstrate a maximum tuning range from 767 to 811 nm. This wavelength range was not addressed by any MECSEL or vertical external-cavity surface-emitting laser device before and extends the available wavelengths for semiconductor based high-quality beam and high-power laser sources to a wavelength window relevant for quantum technology, spectroscopy, or medicine.

Semiconductor membrane external-cavity surface-emitting laser (MECSEL)

Optically pumped semiconductor disk lasers are an important class of solid state lasers. Despite all their advantages, however, they suffer from heat incorporation into the active region caused by the excess energy of the pump photons. To overcome the limits of common methods in thermal management, we realized a semiconductor membrane external-cavity surface-emitting laser (MECSEL) consisting of a diamond heat spreader sandwiched active region design without a monolithically integrated distributed Bragg reflector (DBR). This diamond-sandwich approach improves the heat dissipation out of the active region and makes generally low-heat conductive DBRs obsolete. In an AlGaInP-based system, we demonstrate 595 mW output power at a wavelength of 657 nm and heatsink temperature of 10°C. The MECSEL enables a variety of new material combinations for new laser wavelengths and further potential for power scaling.