High power quantum cascade lasers for environmental monitoring

Background: Quantum cascade lasers (QCLs) are made of layered semiconductor materials and are suited for a variety of applications ranging from environmental monitoring to explosives detection and missile-avoidance systems. The devices emit mid- to long-wavelength infrared radiation and their cores are produced in many stages each stage composed of three regions: an electron injector an active region and an electron extractor. Conventionally the three regions feature quantum well and barrier structures of the same alloy composition respectively. However these QCLs underperform. Specifically maximum wallplug efficiency in continuous wave (CW) operation at room temperature falls far short of predicted limits. Two major challenges are electron leakage and high threshold-current density which describes how much current is needed before a laser can start operating. Partial solutions have been proposed but to maximize efficiencies designs that combat both issues are needed. Technology Description: UW–Madison researchers have developed a design to reduce threshold-current density and virtually suppress electron leakage using certain multiquantum well structures in the active regions of QCL devices. The structures are designed to work reliably over long periods of time at high efficiency and power (i.e. watt range) during quasi-continuous or continuous wave (CW) operation. Known methods may be used to fabricate the semiconductor structure and laser devices and to form the electron injector active region and electron extractor. The active region features a series of quantum wells and barriers of various alloy compositions. The energies of the first and second barrier in the active region are less than the third barrier. Applications: Developing QCLs for environmental monitoring aircraft and security detection