Laser-based Mid-infrared Sources and Applications

4Semiconductor Lasers

Semiconductor mid‐IR lasers are directly driven by a current source, hence they represent the most desirable and compact form of laser. Semiconductor lasers operating at room temperature (RT) have important applications in spectroscopy, remote trace‐gas monitoring, secure communications, and infrared countermeasures, and are used as pump sources for frequency converters based on microresonators and nonlinear waveguides. In this chapter, we will look at four main types of semiconductor lasers: heterojunction lasers, quantum cascade lasers (QCLs), interband cascade lasers (ICLs), and optically pumped semiconductor disk lasers (OPSDLs).

4.1 Heterojunction Mid‐IR Lasers

The emission wavelength of the interband heterojunction diode laser is determined primarily by the bandgap energy of the material used for the active layer (Figure 4.1). Semiconductor lasers operating in the mid‐IR have been around for a long time – the first mid‐IR semiconductor laser was demonstrated by Melngailis in 1963 using InAs, a III–V semiconductor [1]. The InAs laser operated only under pulsed conditions and at cryogenic temperatures. It was soon discovered, however, that IV–VI compound lead‐salt semiconductors such as PbS, PbSn, and PbSe were more promising for the mid‐IR laser action [2]. Indeed, lead‐salt lasers have been used extensively for high‐precision spectroscopy because they can cover a wide emission wavelength range between 3 and 30 μm, provided that one uses a large ...