Interband-cascade lasers (ICLs) produce light from interband transitions, rather than the intersubband transitions of quantum-cascade lasers (QCLs). ICLs, which contain a number of cascade stages and each of which generates photons, produce light in the midwave infrared (MWIR), as do QCLs; one advantage of ICLs is that they have lower dissipated power than QCLs. Researchers at Sotera Defense Solutions (Columbia, MD) and the Naval Research Laboratory (Washington, DC) have developed thermoelectrically cooled gallium antimonide (GaSb)-based ICLs emitting at either 3.2 or 3.45 μm, making them with a 10-stage structure (3.45 μm) as well as an earlier 7-stage structure design (3.23 μm).
For example, an ICL with an 18-μm-wide ridge, 4.5 mm cavity length, and high-reflection/antireflection coatings emitted 464 mW of light at 3.45 μm with a beam-quality factor (M2) of 1.9 and a wall-plug efficiency of around 10% (see figure). Lasers with shorter (1 mm) cavity lengths were also fabricated; these had wall-plug efficiencies that reached 18% at room temperature, although at a lower output power. The researchers note that longer cavities resulted in higher brightness (power per unit area). They believe that the number of stages for a high-power ICL in the 3 to 4 μm range reaches an optimum in the range of 7 to 10. ICLs have many potential uses in MWIR sensing. Reference: M. Kim et al., Opt. Express (Apr. 20, 2015); doi:10.1364/OE.23.009664.
