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

Aggarwal, Roshan L.

Kash, Kathleen

Lindberg, Craig

McManus, J. Barry

People, Roosevelt

Wolff, Peter A.

Yuen, Y. C. Sunny

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X. INFRARED NONLINEAR OPTICSAcademic and Research StaffProf. D.J. Muehlner Dr. R.L. Aggarwal Dr. F. BrownProf. P.A. Wolff Dr. Y.C.S. YuenGraduate StudentsK. Kash C. Lindberg J.B. McManusM.A. Khan R. People1. INFRARED NONLINEAR PROCESSES IN SEMICONDUCTORSU.S. Air Force - Office of Scientific Research (Contract F49620-80-C-0008)Roshan L. Aggarwal, Peter A. Wolff, Y.C. Sunny Yuen, Kathleen Kash,Craig Lindberg, J. Barry McManus, Roosevelt PeopleStudies of resonant, impurity-induced, four-photon mixing in n-Ge are con-tinuing. During the past year, this technique has been used to study the magneticfield dependence of the valley-orbit splitting in Ge:P and Ge:As. The experimentis similar to an ESR measurement - employing fixed-frequency sources and a magneticfield to tune the energy levels. As anticipated, the valley-orbit splitting varieswith magnetic field (B) according to the relation:A(B) = A(O) + aB2Our measurements of a lead to the following conclusions:1. Observed values of a disagree with those predicted by the Lee, Larsen, Laxtheory, but agree with a recent calculation by Dr. Larsen. His resultsshow that a is more sensitive to the form of the donor wave function thanwe had originally expected.2. a increases with increasing donor concentration (in the 10 15-10 16/ccrange), indicating the onset of electron delocalization for n = 10 16/cc.3. Splittings due to off-diagonal matrix elements of the Zeeman interactionare observed in Ge:As.Semiconductor lasers oscillate at a frequency hw = EG; to date, however, laseraction has not been achieved for wavelengths greater than about 30 Ij, despite thePR No. 122(X. INFRARED NONLINEAR OPTICS)fact that in a variety of semiconductor alloys the gap can be continuously variedto zero. It is believed that laser action is precluded (for X > 30 1i) by an ex-ceedingly rapid recombination process, in which electron-hole pairs recombine viaplasmon emission. This process can be controlled by a magnetic field, which modi-fies both the electron-state density and the plasmon dispersion relation. Detailedcalculations suggest that, in large fields, the recombination rate can be reducedenough to permit lasing. Two modes of laser action seem possible - one in whichplasma modes are excited, then radiate via a finite geometry; and another in whicha mixed EM-plasma mode directly emits. Experiments to test these ideas are planned.A theory of Cardona predicts that X 3) of small gap semiconductors varies as-9/2EG . Experiments to test this variation and to explore the resonance enhance-(3)ment of X as hw -+ EG, are in progress. This work will also study the behaviorof X when the difference frequency, wl - W2, is matched to a collective mode ofthe medium. Previous theoretical work indicated strong mixing when Wl - m2 = Wp;similar effects are anticipated when the difference frequency is matched to a pho-non frequency. Both of these processes can serve, in finite geometries, as sourcesof far infrared radiation.References1. R. People, R. Aggarwal, and P.A. Wolff, "Intensity-Dependent Nonlinear Absorp-tion in Ge:P at 10.6," to be published.2. M.A. Khan, D.J. Muehlner, and P.A. Wolff, "Resonant Four-Wave Mixing in n-TypeSilicon," Opt. Cummun. 30, 206 (1979).3. K. Kash, D.J. Muehlner, and P.A. Wolff, "Spin-Induced Optical Mixing in(Hg,Cd)Te" (Abstract), American Physical Society, March 1980.4. R. People, R.L. Aggarwal, and P.A. Wolff, "Off-Diagonal Zeeman Terms in theGround State Manifold of Ge(P)" (Abstract), American Physical Society, March1980.PR No. 122

Infrared Nonlinear Optics

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Infrared Nonlinear Optics

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