Photonic crystals are widely used to control the electromagnetic radiation using local field enhancement properties and photonic bandgap properties allowing for significantly increasing efficiency of nonlinear optical interactions of various types. In our experimental study, we investigated excitation and emission of electromagnetic radiation in synthetic opal matrices. A long afterglow of the samples in the anti-Stokes region of the spectrum, reaching several seconds, was detected. The generation of directed X-ray radiation in the samples was discovered, its temperature and energy thresholds were determined, and the possible physical mechanisms explaining the phenomena observed were explored. The threshold for the occurrence of stimulated low-frequency Raman scattering was on the order of 0.01 GW/cm2 and was determined by the morphology of the sample used. All experiments were carried out in a vacuum, with various liquids such as ethanol, acetone, water and others being used as infiltrates. After using high-speed photography of the electromagnetic glow dynamics of the sample in the optical range, wave-like gigahertz fluctuations in the glow intensity that may be an indication of the relaxational nature of radiation generation in the gigahertz range, were observed.
In this work, the generation of electromagnetic radiation of a wide spectrum, including microwave and terahertz ranges using three-dimensional ordered nanostructures such as photonic crystals were measured. Generation occurred when the exciting electron beam, created by linear accelerator LINAC-200, passed along the planes of orientation of the globules of the photonic crystal. By varying the orientation of the photonic crystal relative to the electron beam and the beam energy, a tunable narrowband microwave and terahertz source with a peak power at 10 W was created. Our experiments involved a set of photonic crystals with different globule diameters and elemental compositions and also included comparative studies using samples of dielectric and semiconductor monocrystals and powders with monodisperse globule sizes. We found that that electromagnetic radiation from single crystals has a similar frequency structure to that of a photonic crystal in the form of a set of narrow-band peaks with a width at half maximum of ~ several MHz appearing in the case, when the beam is passing along the crystallographic orientation axis of the single crystal.
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