Wavelength beam combining of mid-IR semiconductor lasers

Semiconductor lasers operating in the mid-infrared between λ~3-5 μm are of interest for a variety of commercial and military applications. Some applications, such as infrared countermeasures, require multiwatt-class beams with near-diffraction-limited beam quality. Achieving such a high brightness beam from a single semiconductor laser has proven to be challenging at any wavelength. To achieve this goal, we are pursuing the approach of wavelength beam combining (WBC) to scale the brightness of a single laser element, which has relatively low power, by the number of elements in an array. With WBC, the beam quality of the combined beam is close to that of a single element while the power is that of the array. This is achieved by superimposing the beams from individual elements of a laser array, each operating at a different wavelength, both in the near field and far field by means of a dispersive element such as a diffraction grating. We describe the application of WBC to an array of λ~4 μm, broad-area, optically-pumped semiconductor lasers