NASA Scientific and Technical Aerospace Reports

20040073555 State Univ. of New York, Stony Brook, NY
Study of Electron Relaxation Processes in Intersubband Laser Heterostructures
Belenky, G.; Kisin, M.; Suchalkin, S.; Luryi, S.; Mar. 15, 2004; 14 pp.; In English
Contract(s)/Grant(s): DAAD19-00-1-0423
Report No.(s): AD-A422347; ARO-39792.14-EL; No Copyright; Avail: CASI; A03, Hardcopy
Comprehensive experimental and theoretical study of the electron relaxation processes responsible for the depopulation
of the lower lasing slates in intersubband and interhand laser heterostructures has been accomplished. In theory, LO-phonon
assisted relaxation has been given special attention due to the high impact on the laser gain and temperature performance. We
showed that in type-II laser heterostructures LO phonon assisted depopulation of the lower lasing slates is more efficient than
corresponding interband tunneling process. We suggested type-II intersubband laser design with phonon-assisted depopulation
and lower lasing level located near the upper edge of the heterostructure leaky window, where direct interband tunneling
depopulation is inefficient. This design is beneficial for the laser performance providing the highest value of the matrix element
for intrawell optical lasing transition and simultaneously preventing thermal backfilling of the lower lasing states. We also
proposed a piezo-acoustic DFB QCL tunable in a wide wavelength range, which is especially important for spectroscopic
applications of the quantum cascade lasers. Experimental program was focused on the study of temperature dependence of the
optical gain and loss which is the most important factors for laser high-temperature operation. Special measurement technique
has been developed for MIR type- II lasers which allows gain and loss spectra analysis in wide temperature range. Heat
removal and hole leakage processes were also studied using MQW InP-based laser and laser array heterostructures.
DTIC
Lasers; Semiconductor Lasers
20040073603 Naval Research Lab., Washington, DC
Temporally Resolved Langmuir Probe Measurements in LAPPS
Leonhardt, Darrin; Amatucci, WIlliam; Gatling, George; Apr. 12, 2004; 28 pp.; In English; Original contains color
illustrations
Report No.(s): AD-A422457; NRL/MR/6750--04-8761; No Copyright; Avail: CASI; A03, Hardcopy
Electron beams efficiently ionize and dissociate gas, to form low temperature (<1.5 eV) high-density (1O(to the
10)-lO(to the 12)cm(to the -3) plasmas with low internal fields. These plasma sources have culminated in LAPPS, NRL’s
Large Area Plasma Processing System for surface modification of materials. Single Langmuir probes were constructed and
used to determine global plasma parameters (electron temperature, density, and plasma potential) in modulated plasmas
generated by high-energy (2 keV) electron beams. This work describes in detail the construction of probes, applications of
probes in modulated systems and magnetic fields, data acquisition, and data analysis used in the study of electron beam
generated plasmas.
DTIC
Electrostatic Probes; Plasmas (Physics)
20040073687 Agile Materials and Technologies, Inc., Goleta, CA
Thin-Film Phase Shifters
Elsass, Chris; Sep. 9, 2003; 6 pp.; In English; Original contains color illustrations
Contract(s)/Grant(s): DAAD19-00-C-0100
Report No.(s): AD-A422587; ARO-41271.1-MS; No Copyright; Avail: CASI; A02, Hardcopy
This work has concentrated on developing thin-film tunable dielectric technology towards commercial viability for
phase-shifters. Agile’s varactor and phase shifter modeling has demonstrated the potential for this technology to provide low
loss phase shifters utilizing Barium Strontium Titanate (BST) as the tunable dielectric material. Initial work involved
fabrication of parallel plate capacitors as test structures which demonstrated the high quality of the BST films. Prototype
phase-shifters utilizing such films were successfully demonstrated and issues such as intermodulation distortion (IMD) were
explored and quantified in terms of design parameters. This technology was also compared with alternatives such as MEMS
and GaAs MMICs. Specifically, the tradeoff between control voltage and performance variables such as IMD, power handling,
and phase noise was explored and tabulated for the various approaches. Agile’s varactors technology enables low cost,
low-loss phase shifters for DOD and commercial applications.
DTIC
Barium Titanates; Strontium Titanates; Thin Films
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