Gain Crystals for Yellow Lasers.

We offer a novel laser crystal that enables simple realization of compact lasers with emission in the visible spectral range.

Excellent Beam Quality. Watt-Level.​

MEXL technology allows our customers to fabricate efficient laser sources with output powers ranging from a few milliwatts to several watts. A diffraction-limited beam profile is inherent to the system.

MHz Modulation. Simple.​

Lasers based on MEXL gain crystals can be modulated directly via the input current. No additional devices are required.

Photography by Marieke Lienert

Yellow Lasers based on MEXL-Technology

The MEXL (Membrane External Cavity Laser) is an optically pumped laser system that combines the advantages of solid-state and diode lasers. While the gain is provided by a thin semiconductor membrane with fundamental emission in the near-infrared region, the external resonator provides access for optical elements to tailor the laser properties. This allows the enormous power in the cavity to be used for highly efficient second harmonic generation to achieve watt-level continuous-wave laser emission in the green-yellow spectral range. Since an external mirror defines the laser mode, the membrane laser inherently provides a perfect beam profile that enables low-loss coupling to single-mode optical fibers. At the same time, the short upper-state lifetime of the semiconductor gain ensures low-noise operation and enables modulation at frequencies up to the MHz range by simply modulating the input current of the optical pump diode. The result is an ultra-compact source of visible laser radiation with high modulation capabilities.

MEXL Gain Crystal

The MEXL gain crystal represents the core of the membrane laser. It is based on a µm-thin semiconductor membrane sandwiched between two optically transparent heat spreaders. By altering the material composition of the membrane, the laser emission wavelength is adjusted during the fabrication process. Our currently available crystals cover the range from 500nm to 600nm, further wavelengths are to come!
For easy implementation, each gain crystal comes with multifunctional dielectric coatings in a 2mm diameter aperture. On one side, the coating is highly reflective for the laser wavelength and serves as cavity end mirror. At the same time, this coating is transparent for wavelengths between 800nm and 830nm. Any wavelength in this range is ideal for optical pumping of the semiconductor gain membrane. The surfaces outside the coated apertures are gold-plated for optimized thermal connection via soldering.
From the bare semiconductor substrate to the diced gain crystal, all fabrication steps are performed at the wafer level and monitored throughout the whole production process. In the last step, each individual gain crystal has to pass a final inspection to ensure consistently high quality.

III-V Semiconductor Epitaxy

We fabricate our gain membranes via Metal-Organic Vapor-Phase Epitaxy (MOVPE), which is the latest production technology for ultra-thin single-crystalline layers of III-V semiconductor compounds. The company’s core expertise includes the layer design as well as the analysis and quality assurance of semiconductor gain structures. Our engineering team performs the epitaxial growth in-house using two state-of-the-art machines. By precisely controlling the process parameters, we achieve excellent material homogeneity and highest reproducibility. This ensures that each MEXL laser performs at the highest level.



Universität Stuttgart
Allmandring 3
70569 Stuttgart



Twenty-One Semiconductors GmbH
Kiefernweg 4
72654 Neckartenzlingen