Toward 3 micron wavelength semiconductor disk lasers

There are numerous industrial, medical, and security-related applications for which high-brightness, flexible laser sources emitting at IR wavelengths in the 2–3 m range are highly desirable. They include long-range sensing—such as light detection and ranging (LIDAR) for clear-air turbulence or gas detection—long-range free-space optical communications, as well as medical diagnostics and therapy. Medical applications make use of the distinct absorption features of human tissue (which are mostly determined by water absorption) at 2 and 2.9 m, making these wavelengths ideal for high-precision laser scalpels. This has driven the development of a new category of semi-conductor laser, long-wavelength optically pumped semi-conductor disk lasers (OPSDLs), also known as vertical external-cavity surface-emitting lasers (VECSELs).1 In the 1 m wavelength range, with laser structures based on the gallium arsenide (GaAs) material system, OPSDLs with output powers of up to several tens of Watts have been realized.2 Most recently, these lasers have entered the commercial market with great success, either with their fundamental laser emission around 1 m or frequency doubled to cover the visible range.2, 3 At wavelengths longer than 1 m, however, the output power and efficiency of OPSDLs generally degrade, and often significantly so. We have developed a mature OPSDL technology based on the group III-antimonide material system to take advantage of the 2 m wavelength range. In demonstrating the first 2.8 m room-temperature continuous-wave (CW) OPSDL, we have further expanded the wavelength range of this class of semiconductor laser. This was possible through the combined effect of improved semiconductor structure design, and better molecularbeam-epitaxy (MBE) fabrication steps. The MBE growth of this Figure 1. Optically pumped semiconductor disk laser (OPSDL) structure with transparent heat spreader, mounted inside a submount.