kvantdalskaskadlaser

Kvantdalskaskadlaser, in Swedish often used to refer to the quantum cascade laser, is a type of semiconductor laser that emits coherent infrared light through intersubband transitions in a cascaded quantum-well structure. In a single device, electrons pass through a series of identical active regions, emitting a photon at each stage. This cascaded design allows substantial output power and the engineering of emission wavelengths across a broad mid- to far-infrared range, without relying on traditional interband recombination.

Construction and operation are based on highly engineered semiconductor heterostructures. The active region consists of repeated quantum wells and barriers that create discrete energy subbands. Electrons are injected into the upper subband, relax via a radiative transition to a lower subband, and then are transported to the next stage, continuing the cycle. The emission wavelength is determined by the intersubband transition and can be tailored over a wide spectral range. Waveguides and optical cavities, such as ridge waveguides or distributed feedback structures, provide confinement and mode selection.

Materials and performance vary by wavelength target. Mid-infrared designs commonly use InP- or GaAs-based systems with InGaAs/AlInGaAs or GaInAs/AlInGaAs active regions, while terahertz versions use different lattice-matched materials. Practical devices require careful thermal management; many operate at cryogenic temperatures, though ongoing research aims for higher-temperature or room-temperature operation. Applications include spectroscopy, trace-gas sensing, environmental monitoring and integrated photonic systems, where narrow-linewidth, tunable infrared sources are valuable.

The concept emerged in the 1990s, with notable contributions from Capasso and Faist and colleagues, and has since evolved into a mature platform for compact, electrically pumped infrared lasers and frequency-comb sources.