Experimental Study of the Effect of External Signal on Microwave Oscillations in a Nonrelativistic Electron Beam with Virtual Cathode

The effect of an external harmonic signal on the characteristics of microwave generation in a nonrelativistic electron beam with virtual cathode (VC) formed in a static retarding electric field (low-voltage vircator system) has been experimentally studied. A significant increase in the vircator generation power is observed when the frequency of the external signal is close to the frequency of VC oscillations. At large detunings, a broadband chaotic generation is observed.Comment: 3 pages, 2 figure

HgCdTe-based quantum cascade lasers operating in the GaAs phonon Reststrahlen band predicted by the balance equations method

HgCdTe-based quantum cascade lasers operating in the GaAs phonon Reststrahlen band with a target wavelength of 36 mkm are theoretically investigated using the balance equations method. The optimized active region designs, which are based on three and two quantum wells, exhibit a peak gain exceeding 100 cm(-1) at 150 K. We analyze the temperature dependences of the peak gain and predict the maximum operation temperatures of 170 K and 225 K for three- and two-well designs, respectively. At high temperatures (T > 120 K), the better temperature performance of the two-well design is associated with a larger spatial overlap of the weakly localized lasing wavefunctions as well as a higher population inversion

Effect of heating and cooling of photogenerated electron-hole plasma in optically pumped graphene on population inversion

We study the characteristics of photogenerated electron-hole plasma in optically pumped graphene layers at elevated (room) temperatures when the interband and intraband processes of emission and absorption of optical phonons play a crucial role. The electron-hole plasma heating and cooling as well as the effect of nonequilibrium optical phonons are taken into account. % The dependences of the quasi-Fermi energy and effective temperature of optically pumped graphene layers on the intensity of pumping radiation are calculated. The variation of the frequency dependences dynamic conductivity with increasing pumping intensity as well as the conditions when this conductivity becomes negative in a certain range of frequencies are considered. % The effects under consideration can markedly influence the achievement of the negative dynamic conductivity in optically pumped graphene layers associated with the population inversion and, hence, the realization graphene-based terahertz and infrared lasers operating at room temperatures.Comment: 12 pages, 7 figure

Investigation of the Chaotic Dynamics of an Electron Beam with a Virtual Cathode in an External Magnetic Field

The effect of the strength of the focusing magnetic field on chaotic dynamic processes occurring inan electron beam with a virtual cathode, as well as on the processes whereby the structures form in the beamand interact with each other, is studied by means of two-dimensional numerical simulations based on solving a self-consistent set of Vlasov-Maxwell equations. It is shown that, as the focusing magnetic field is decreased,the dynamics of an electron beam with a virtual cathode becomes more complicated due to the formation andinteraction of spatio-temporal longitudinal and transverse structures in the interaction region of a vircator. The optimum efficiency of the interaction of an electron beam with the electromagnetic field of the vircator isachieved at a comparatively weak external magnetic field and is determined by the fundamentally two-dimensional nature of the motion of the beam electrons near the virtual cathode.Comment: 12 pages, 8 figure