“…The wide-aperture THz beam propagates through the phase axicon, which is formed by the corresponding amplitude-phase transmission in the approximation of an infinitely thin phase object. According to works 41 , 42 original THz pulse is a single-cycle pulse, whose electric field amplitude E ( t ) can be represented by the following function: Figure 8 Scheme of the propagation of pulsed THz radiation through the phase axicon with the formation of a Gauss-Bessel beam. A collimated wide-aperture THz beam illuminates the phase axicon located at the distance z from the ZnTe detection crystal.…”
Terahertz pulse time-domain holography is the ultimate technique allowing the evaluating a propagation of pulse broadband terahertz wavefronts and analyze their spatial, temporal and spectral evolution. We have numerically analyzed pulsed broadband terahertz Gauss-Bessel beam’s both spatio-temporal and spatio-spectral evolution in the non-paraxial approach. We have characterized two-dimensional spatio-temporal beam behavior and demonstrated all stages of pulse reshaping during the propagation, including X-shape pulse forming. The reshaping is also illustrated by the energy transfer dynamics, where the pulse energy flows from leading edge to trailing edge. This behavior illustrates strong spatio-temporal coupling effect when spatio-temporal distribution of Bessel beam’s wavefront depends on propagation distance. The spatio-temporal and spatio-spectral profiles for different spectral components clearly illustrate the model where the Bessel beam’s wavefront at the exit from the axicon can be divided into radial segments for which the wave vectors intersect. Phase velocity via propagation distance is estimated and compared with existing experimantal results. Results of the phase velocity calculation depend strongly on distance increment value, thus demonstrating superluminal or subluminal behavior.
“…The wide-aperture THz beam propagates through the phase axicon, which is formed by the corresponding amplitude-phase transmission in the approximation of an infinitely thin phase object. According to works 41 , 42 original THz pulse is a single-cycle pulse, whose electric field amplitude E ( t ) can be represented by the following function: Figure 8 Scheme of the propagation of pulsed THz radiation through the phase axicon with the formation of a Gauss-Bessel beam. A collimated wide-aperture THz beam illuminates the phase axicon located at the distance z from the ZnTe detection crystal.…”
Terahertz pulse time-domain holography is the ultimate technique allowing the evaluating a propagation of pulse broadband terahertz wavefronts and analyze their spatial, temporal and spectral evolution. We have numerically analyzed pulsed broadband terahertz Gauss-Bessel beam’s both spatio-temporal and spatio-spectral evolution in the non-paraxial approach. We have characterized two-dimensional spatio-temporal beam behavior and demonstrated all stages of pulse reshaping during the propagation, including X-shape pulse forming. The reshaping is also illustrated by the energy transfer dynamics, where the pulse energy flows from leading edge to trailing edge. This behavior illustrates strong spatio-temporal coupling effect when spatio-temporal distribution of Bessel beam’s wavefront depends on propagation distance. The spatio-temporal and spatio-spectral profiles for different spectral components clearly illustrate the model where the Bessel beam’s wavefront at the exit from the axicon can be divided into radial segments for which the wave vectors intersect. Phase velocity via propagation distance is estimated and compared with existing experimantal results. Results of the phase velocity calculation depend strongly on distance increment value, thus demonstrating superluminal or subluminal behavior.
“…The effect of frequency conversion is convenient to describe in the time domain. We consider a Gaussian pulse in the form of a sinusoidal carrier modulated by a slowly varying envelope [53,54]:…”
Section: Time Domain and Spectral Analysismentioning
The recently developed concept of time-varying metamaterials paves the way for advanced methods of electromagnetic property modulation, such as magnet-free isolators, frequency converters, and other nonreciprocal photonic components. Here, we analyze the metamaterial based on the periodically arranged temporally modulated graphene layers via a steplike graphene Fermi level. The material properties are described by the effective medium theory. The electromagnetic wave temporal scattering phenomenon caused by rapid steplike graphene Fermi level switching is considered. It is demonstrated that the frequency of scattered waves increases as the Fermi level grows rapidly and vice versa. The relation between the amplitudes of forward-and backward-scattered waves is found using the Laplace transform technique. The proposed concept allows us to efficiently generate frequency harmonics under instant switching of the graphene Fermi level at a few meV. Our investigation provides a basement for the realization of temporally modulated multilayer structures based on functional tunable materials as power-efficient frequency converters.
“…Остался нерассмотренным вопрос влияния колебаний тяжелых ионов среды, в которую помещены углеродные нанотрубки, и поглощения ими электромагнитного поля. Учет данного воздействия важен при исследовании распространения предельно коротких оптических импульсов в нелинейных дисперсионных средах, что подтверждается, например, работами [14,15]. Поглощение на таких ионах может значительно сузить диапазон прозрачности и уменьшить ширину спектра пропускания в среде с углеродными нанотрубками.…”
Исследовано распространение электромагнитных волн в среде с зигзагообразными уг леродными нанотрубками. На основании уравнений Максвелла получено эффективное уравнение для вектор-потенциала электромагнитного поля, в котором учтены колебания ионов диэлектрической среды, в которую помещены нанотрубки. Выявлена зависимость формы импульса от характера колебаний тяжелых ионов, на которых может происходить поглощение электромагнитного поля, а также от других параметров задачи.
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