Accession Number : ADA516390


Title :   High-Efficiency and High-Power Mid-Wave Infrared Cascade Lasers


Descriptive Note : Interim rept. 1 Feb 2007-31 Jul 2009


Corporate Author : PRINCETON UNIV NJ DEPT OF ELECTRICAL ENGINEERING


Personal Author(s) : Gmachl, Claire


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a516390.pdf


Report Date : Aug 2009


Pagination or Media Count : 65


Abstract : Quantum cascade laser (QCL) performance continues to improve towards the requirements of applications such as infrared counter measures. However, key metrics, such as wall-plug efficiency (WPE), are still not fully met. DARPA's EMIL program continues to support progress in QCLs, and this report summarizes the Princeton team's work during Phase I of this program. Although the work systematically addressed all major facets of efficiency, the greatest advancements involved injection designs, which improved almost all efficiency components. Strain compensated QCLs with heterogeneous injectors produced low voltage defect. The active core consisted of interdigitated undoped and doped injectors followed by nominally identical optical transitions. The undoped injectors were designed with reduced voltage defect while the doped injector designs were more conventional. The measured average voltage defect was less than 79 meV. At 80 K, a 2.3 mm long, back facet high reflectance coated laser had an emission wavelength of 4.7 micrometers and output 2.3 W pulsed power with 19% peak WPE. Other QCLs emitting at 4.2 micrometers featured a low voltage defect and short injector with only four quantum wells. Devices with a voltage defect of 20 meV and a record voltage efficiency of 91% were demonstrated for pulsed operation at 180 K. Voltage efficiencies of greater than 80% were exhibited at room temperature. WPEs ranging from 21% at cryogenic temperatures to 5.3% at room temperature were achieved. Interface roughness effects were analyzed as in homogeneous broadening, explaining the temperature dependent QCL gain spectra and suggesting improved designs. Specifically, density-matrix theory revealed benefits from stronger coupling between injector and upper laser level that led to low-temperature pulsed QCLs nearing 50% WPE.


Descriptors :   *CASCADE STRUCTURES , *GALLIUM ARSENIDE LASERS , *INTERMEDIATE INFRARED RADIATION , *QUANTUM WELL LASERS , *EFFICIENCY , *GALLIUM ARSENIDES , *QUANTUM WELLS , *INFRARED COUNTERMEASURES , *ALUMINUM GALLIUM ARSENIDES , LASERS , ROOM TEMPERATURE , REDUCTION , SHORT RANGE(TIME) , COATINGS , SPECTRA , PULSES , GAIN , OPERATION , HETEROGENEITY , TRANSITIONS , REFLECTANCE , INFRARED RADIATION , INJECTORS , ROUGHNESS , CRYOGENICS , COUNTERMEASURES , LOW VOLTAGE , VOLTAGE , TEAMS(PERSONNEL) , QUANTUM THEORY , INTERFACES , CORES , LOW TEMPERATURE , OPTICAL PROPERTIES , EMISSION , FREQUENCY , REQUIREMENTS


Subject Categories : Electrical and Electronic Equipment
      Lasers and Masers
      Countermeasures
      Infrared Detection and Detectors
      Quantum Theory and Relativity


Distribution Statement : APPROVED FOR PUBLIC RELEASE