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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Anti-Stokes Cryoluminescence in Nanomaterials
摘要： Study of the electromagnetic fields interaction with structured nanomaterials with photonic band gaps is one of the most rapidly developing areas of nanophotonics. In modern optics, such nanomaterials are actively used to process the characteristics of electromagnetic radiation. Firstly, the properties of amplification of the local field are used, secondly, the properties of the photonic bandgap. A typical example of local field amplification is the work [1], in which the authors used a coating of submicron dielectric spheres on a copper target in order to achieve more than tenfold increasing the efficiency of X-ray generation. Using the properties of the photonic band gap leads to the increasing well-known nonlinear effects efficiency and to the appearance of new nonlinear phenomena. One of these phenomena is anti-Stokes cryoluminescence in nanomaterials - light emission at low temperature under laser action in the spectral range with higher frequency than that of exciting light. We observed bright and long (up to few seconds) emission in blue-green range under 20ns ruby laser pulses excitation in different nanomaterials at low temperatures [2-3]. One of the reasons of this effect is triboluminescence, free radicals appearing and structure defects forming, like in bulk materials [4]. In the present work we show that in nanomaterials of different nature there are two types of temporal dependence: short (few microseconds) and long (up to 10-12 seconds). Long dependence exists at temperatures lower than 110 K. Temporal dependence for anti-Stokes luminescence in synthetic opal matrices for temperatures lower and higher this threshold is shown in Figure 1.
关键词： anti-Stokes cryoluminescence,nanophotonics,electromagnetic radiation,photonic band gaps,nanomaterials
更新于2025-09-11 14:15:04
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Photoinduced Local Nonequilibrium States in Superconductors: Hot Spot Model
摘要： The so-called hot spot model is often used to study problems concerning the local heating of electrons and phonons and local suppression of superconductivity by electromagnetic radiation. This model implies that the dynamics of a system in a certain time interval can be described by a locally equilibrium electron distribution function, but the electron temperature Te differs from the equilibrium value. Such an assumption makes it possible to use the heat equation to study the temporal and spatial dynamics of Te and significantly simplifies the study of the dynamic response of a superconductor. Examples of the use of this model to describe nonequilibrium effects occurring in systems with different types of superconducting pairing under electromagnetic irradiation have been presented in this work.
关键词： hot spot model,superconductivity,nonequilibrium effects,electromagnetic radiation
更新于2025-09-10 09:29:36
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High-power terahertz emission from a plasma penetrated by counterstreaming different-size electron beams
摘要： It is found that multi-cycle pulses of high-power coherent terahertz radiation can be efficiently generated in a plasma by counterstreaming long-pulse electron beams driving potential plasma waves via the two-stream instability. Instead of the well-known three-wave interaction processes between oblique beam-driven modes, we propose to generate electromagnetic radiation near the doubled plasma frequency due to the novel and much more efficient mechanism based on the head-on collision of longitudinal plasma waves with mismatching potential profiles. It is shown that this radiation mechanism can be implemented experimentally either by the collision of low-density electron beams with different transverse sizes or by the counter injection of denser equal-size beams unstable against filamentation perturbations. Particle-in-cell simulations for kiloampere electron beams capable of focusing into millimeter-scale sizes demonstrate the possibility to reach the high efficiency of beams-to-THz power conversion (3%–7%), which opens the path to gigawatt-class THz sources with a narrow spectral line.
关键词： electromagnetic radiation,two-stream instability,plasma,electron beams,terahertz emission
更新于2025-09-10 09:29:36