Contains report on one research project.U.S. Air Force - Office of Scientific Research (Contract F49620-80-C-0008

Aggarwal, Robert L.

Jagannath, Chiravurri

Kash, Kathleen

McManus, J. Barry

People, Roosevelt

Vérié, Christian J.

Wolff, Peter A.

Youngdale, Eric P.

Yuen, Y. C. Sunny

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X. INFRARED NONLINEAR OPTICSAcademic and Research StaffProf. P.A. Wolff Dr. F. Brown Dr. C.J. VdrieDr. R.L. Aggarwal Dr. C. Jagannath Dr. Y.C.S. YuenDr. L.R. Ram-MohanGraduate StudentsK. Kash C. Lindberg J.B. McManusR. People E.P. YoungdaleI. INFRARED NONLINEAR PROCESSES IN SEMICONDUCTORSU.S. Air Force - Office of Scientific Research (Contract F49620-80-C-0008)Roshan L. Aggarwal, Peter A. Wolff, Christian J. Veri6, Chiravurri Jagannath,Y.C. Sunny Yuen, Kathleen Kash, J. Barry McManus, Roosevelt People, Eric P.YoungdaleAs a preliminary to high-field, four-wave mixing experiments in (Hg,Cd)Te,extensive studies of below-gap, IR absorption have been performed in this mate-rial. Crystals studied included samples from Honeywell, Cominco, and CNRS (pro-vided by C.J. V'rie). At helium temperatures, the absorption coefficient is nearlyindependent of frequency (below the gap) and ranges from 3-50 cm-1. As tempera-ture is raised, increased absorption due to intervalence-band transitions andfree-carrier absorption is observed. Values of a , 10 cm-1 preclude the use of(Hg,Cd)Te as a nonlinear material. Thus, the origin of the 40K absorption is nowbeing sought. Its variation from sample to sample, and near constancy in fre-quency, argue for a defect absorption mechanism.A careful study of the power dependence of CO2 laser absorption in n-Ge hasrecently been completed. This work, in contrast to previous experiments alongthese lines, employed a single-mode TEA laser which provides smooth pulses. Theabsorption coefficient of cold n-Ge crystals was observed to decrease markedly(from 1 cm-1 to below 0.1 cm-1) with laser power. The results have been inter-preted with a two-level kinetic model which balances the photoionization rate (fromdonors) against the capture rate (of free electrons). The fit determines thePR No. 123(X. INFRARED NONLINEAR OPTICS)photoionization, free-carrier, and capture cross sections.Calculations of plasmon gain and pumping threshold for narrow-gap semiconduc-tors with EG = f-wp are continuing. The ultimate aim of this work is the develop-ment of a plasmon laser. The theory indicates that magnetic fields enhance thegain, via Landau-level quantization, and reduce the minority carrier recombinationrate through modification of the plasmon dispersion relation. The optimal situa-tion occurs in semimetallic (Hg,Cd)Te with field-induced gap; thresholds below100 kW/cm 2 are predicted under these circumstances.References1. Roosevelt People, "Resonant Nonlinear Optical Spectroscopy of MagneticallyTunable Donor Impurity States in Germanium," Ph.D. Thesis, Department ofPhysics, M.I.T., September 1980.2. R.L. Aggarwal, R. People, P.A. Wolff, and D.M. Larsen, "Effect of MagneticField on the Valley-Orbit Split ls States of Shallow Donors in Germanium,"Proceedings of the XVth International Conference on the Physics of Semicon-ductors, Tokyo, Japan, 1980.3. J.B. McManus, R. People, R.L. Aggarwal, and P.A. Wolff, "Nonlinear AbsorptionDue to Shallow Donors in Germanium at 10.6 p," submitted for publication inJAP.4. R. People and P.A. Wolff, "Effects of the Off-Diagonal Zeeman Interaction onthe Ground State of Donors in Germanium," to be published.PR No. 123

Infrared Nonlinear Optics

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Infrared Nonlinear Optics

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