Dilute nitrides tailor the wavelength of semiconductor disk lasers

Abstract

Interest is growing rapidly in efficient and compact optically pumped semiconductor disk lasers (OP-SDLs) since they provide a practical solution for generating high-power radiation at visible wavelengths. In particular, red-green-blue SDLs are thought to satisfy the demanding requirements of laser displays and projectors. Other applications, such as spectroscopy and biomedicine, are also expected to benefit greatly from the wavelength versatility and excellent beam quality offered by OPSDLs. Also known as vertical external cavity surface-emitting lasers,1, 2 OP-SDLs combine many of the advantages of traditional solid-state lasers with the versatility offered by semiconductor gain materials. Such laser sources can deliver Watt-level diffraction-limited output beams in a broad spectral range determined by the gain material. The key element of an OP-SDL is the semiconductor gain mirror, which is placed in an external laser cavity configuration, as shown in Figure 1. This arrangement allows a nonlinear crystal to be placed into the cavity for frequency conversion. The most notable results demonstrated with visible SDLs have been obtained in the blue-green region by frequency doubling 940nm and 1060nm laser radiation.3 However, the development of frequency-doubled OP-SDLs at red-orange wavelengths has been hindered by the lack of suitable semiconductor materials for fabricating high-quality gain mirrors operating at around 1200–1250nm. To tackle this problem, we have developed gallium indium nitride arsenide / gallium arsenide (GaInNAs/GaAs) gain regions that can be integrated with highquality gallium arsenide / aluminum arsenide (GaAs/AlAs) distributed Bragg reflectors (DBRs). DBRs act as mirrors for a specific wavelength range related to the optical thickness of Figure 1. Schematic of an OP-SDL with an intra-cavity heat-spreader.