Above 2-µm emitting GaSb-based semiconductor disk laser with <100-kHz linewidth at 1000-mW output power

In this paper we report on the development of narrow-linewidth vertical-external-cavity surface-emitting laser (VECSEL) at a wavelength of >2 µm. Starting from a laboratory setup, we designed a highly stable VECSEL module machined from a solid block of aluminum. For linewidth precise measurements, heterodyne beatnote measurements were employed. For this firstgeneration module a linewidth of 9 kHz was achieved when actively stabilizing the laser wavelength, whereas without stabilization the linewidth amounted to 45 kHz at an output power of 100 mW, both data referring to a 100-µs sampling time. To further increase the output power, a secon-generation module was fabricated, for which the on-chip mode diameter was increased. This allowed operation at a larger pump-spot diameter and still maintaining TEM00 operation, while increasing the maximum pump power and hence the output power. This module yielded an output power above 1 W in single-mode operation at a linewidth of 60 kHz (100 µs sampling time) without active wavelength stabilization. Modehop-free single-mode operation could be maintained for more than 18 hours. This new multiple-Watt, narrow-linewidth VECSEL module is apt for plane-to-ground communications without the necessity of amplifiers.