Generation of High-Frequency Radiation in the Conditions of Superradiance of Particles with a Constant Dipole Moment
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Generation of High-Frequency Radiation in the Conditions of Superradiance of Particles with a Constant Dipole Moment A. M. Basharova,b,* and A. I. Trubilkoc a National
Research Center Kurchatov Institute, Moscow, 123182 Russia Institute of Physics and Technology, Dolgoprudnyi, Moscow oblast, 141701 Russia c St. Petersburg University of State Fire Service, Ministry of Emergency Situations of Russia, St. Petersburg, 196105 Russia *e-mail: [email protected]
b Moscow
Received December 15, 2019; revised January 12, 2020; accepted January 15, 2020
Abstract—A localized ensemble of identical particles with a constant dipole moment generates during superradiance a coherent pulse of low-frequency radiation, the pulse shape depending significantly on the number of particles in the ensemble. In particular, low-frequency radiation pulse is transformed from one-hump to two-hump shape in a narrow range of variation of ensemble parameters. DOI: 10.1134/S1063776120050131
1. INTRODUCTION Electromagnetic processes in media with a constant dipole moment (CDM) (e.g., ensembles of quantum dots) attract attention as regards practical applications (generation of low-frequency terahertz radiation) as well as the general theory. It is assumed that electromagnetic frequencies from 0.1 to 10 THz (wavelengths in the range 1– 0.01 mm) belong to the terahertz radiation range. Terahertz radiation effectively interacts with vibrational, rotational, tunneling, etc. quantum transitions, which is promising for spectroscopy. However, it is difficult to obtain terahertz radiation with laser generation of coherent radiation: thermal effects are significant because a quantum of 1 THz corresponds to temperature of about 50 K. For this reason, the methods for generating terahertz radiation based on optical rectification and/or application of femtosecond optical pulses are quite popular (see reviews [1, 2]). We will subsequently consider low-frequency radiation because, depending on the context, the ratio of frequencies of involved quantum transitions and the emergence of polarization at frequencies much lower than the frequencies of operative quantum transitions is important for our analysis, and exceedance of the outlined terahertz radiation range is also possible. Most theoretical publications on the generation and interaction of low-frequency radiation deal with numerical simulation of processes. The number of publications in which various problems of integrability of equations (see, for example, [2–11]), processes occurring in optically thin media [12, 13] and microcavities (see, for example, [14]) is scarce.
In this article, we propose a simple and analytically solvable model of generation of low-frequency radiation by an ensemble of superradiant particles with a CDM. We have obtained expressions for the low-frequency radiation intensity occurring in the special superradiance regime that is referred here as the nonWiner regime [15, 16]. This regime differs from the standard superradiance regime [17] for a localized ensemble of
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