Development of Quantum Cascade Laser Heterostructures for Mid-Infrared (4-5 Micron) Atmospheric Transmission

This proposal will demonstrate the feasibility and design of quantum cascade lasers for ambient temperature free-space communication in the mid-infrared (4-5 microns). An ideal system would include an uncooled, compact, and durable source of laserradiation in this wavelength range. Conventional semiconductor laser technology has so far been unable to produce high power lasers in this wavelength range without optical pumping and/or cryogenic cooling. The quantum cascade laser, while demonstratingexcellent performance for lambda >5 microns, is relatively undeveloped in the 4-5 micron wavelength range, which is suitable for free space communication. This is due, in part, to the necessary use of highly mismatched materials in a strain-balancedconfiguration. In Phase I, determination of the output power and duty cycle required for free-space communication will be investigated. A systematic approach to optimizing the high duty cycle performance of a highly strain-compensated quantum cascadelaser will then be undertaken, focusing on material growth, doping distribution, material characterization, and room temperature, high-duty cycle, testing data. Current free space optical systems are hindered by scattering elements (such as fog or smoke)and scintillation effects. Both act to shorten or completely sever a free space optical link. As predicted by scattering and scintillation theory, a mid-infrared laser source should have superior transmission through a non-ideal atmosphere as compared toa commercially available near-infrared source. This significant performance boost is especially noticeable in a somewhat dense smoke or fog condition, which is one of many likely atmospheric conditions on a battlefield. As it is most important tomaintain contact in precisely these conditions, the development of a longer wavelength optical link can potentially save many lives due to uninterrupted intelligence. A secondary benefit of this work is the eventual development of a high power lasermodule for potential use in other areas, such as remote chemical sensing or infrared countermeasures, both of which are extremely important in the commercial and/or military arena.