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.