Membrane-external-cavity surface-emitting lasers (MECSELs) were originally demonstrated by Prof. Mansoor Sheik-Bahae’s group at the University of New Mexico (UNM) in 2015. MECSELs consist of an epitaxial active region combined with at least one transparent heatspreader, typically SiC or diamond, employing external cavity mirrors for feedback. The standalone gain element allows for significant flexibility in emission wavelength and is amenable to enhanced power scaling via optimized thermal management. In an extremely fruitful collaboration with UNM beginning in 2017, we progressed from serially-produced chip-scale prototypes, to 4” wafer-scale manufacturing of double-bonded (SiC/epi/SiC) devices capable of single-mode frequency-doubled output powers in excess of 10 W. Leveraging this unique architecture, we see a bright future ahead for multi-Watt-output optically-pumped semiconductor laser systems emitting throughout the visible and infrared spectral regions.
A mode-locked VECSEL is reported using a novel hybrid semiconductor saturable absorber mirror (SESAM) consisting of a semiconductor absorber region bonded to a curved dielectric partial reflector. The hybrid SESAM is realized by direct bonding of the saturable absorber to a commercially available ultrafast output coupler, nominally 99.4% reflectivity and GDD of ≤ |20 fs2| with a radius of curvature of 10 cm. In a linear cavity where the curved output coupler is the hybrid SESAM, a pulse-width of 410 femtoseconds is achieved at a repetition rate of 4.2 GHz for a VECSEL operating at a wavelength of 1030 nm.
We outline the development of a high-power-handling deformable mirror device, based on a modified Thorlabs DMH40, employing a low-loss substrate-transferred crystalline coating as the reflective element. In standard products, this system features a metal coated (Ag or Al) 18 mm diameter × 150 μm thick BK10 glass substrate mounted to a 40-segment piezoelectric actuator, enabling Zernike compensation up to 4th order, with a peak-to-valley stroke up to ±17.6 μm. In the modified variant described here, the metal coating is replaced with a high-reflectivity (~99.998%) and low-stress (compressive, ~130 MPa) monocrystalline GaAs/AlGaAs Bragg stack transferred to the thin glass substrate via direct bonding. While maintaining similar physical performance, this custom system exhibits a substantial enhancement in power handling, with laser-induced damage tests (performed by Spica Technologies, Inc.) yielding a continuous-wave damage threshold of 75 MW/cm2 at 1070 nm with a 1/e2 spot diameter of 32.8 μm.
Membrane-external-cavity surface-emitting lasers (MECSELs) consist of an epitaxial active region directly bonded to at least one transparent heatspreader with external cavity mirrors for feedback. This structure enables significant flexibility in the emission wavelength and yields a standalone laser gain medium amenable to enhanced power scaling via optimized thermal management. We outline a 4” wafer-scale manufacturing process for dual-SiC-heatspreader (SiC/epi/SiC) gain chips, incorporating external dielectric coatings and metallization for intimate mounting to a heatsink. Our process leverages low-temperature wafer bonding in concert with traditional deposition, lithography, and etching steps, allows hundreds of MECSEL gain chips to be simultaneously produced.
DBR-free VECSELs overcome long-standing limitations in standard devices and offer improved heat management, reduced growth complexity, larger material choice, and broader gain tunability. We present the latest advances in DBR-free VECSELs emitting at 1178 nm targeting sodium guide star applications. We compare barrier-pumping and in-well pumping schemes employing 808 nm and 1070 nm pump lasers, respectively. A maximum output power of >20 W is attained with the barrier-pumping configuration, while a ~52 % slope efficiency with single pass is obtained with the in-well pumping scheme. Linewidth narrowing of < 0.25 nm and frequency conversion to 589 nm is also presented.
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