Transparent Dielectric Medium Research Articles

Understanding a spectral response in a metal–dielectric–metal cavity structure: The role of constituent metals

Understanding optical interference in multilayer structures is of critical importance for designing a variety of optical coatings that have been widely used as an essential element in diverse applications. We demonstrate that the transition of reflective properties from a valley to a peak occurs by a metal on the incident side in a cavity structure comprising a transparent dielectric medium surrounded by two metals. The reflected light destructively interferes giving rise to a reflection dip when there is a large difference between the refractive index and the extinction coefficient of the metal, whereas a constructive interference occurs with the refractive index that is comparable to the extinction coefficient yielding a reflection peak. In addition, an admittance and an electric field distribution of the cavity structure are investigated with different constituent metals. Our results described in this paper provides a better understanding of the fundamental principles of the optical cavity, thereby potentially extending the range of possible future applications.

Radiation shift from triple to quadruple frequency caused by the interaction of terahertz pulses with a nonlinear Kerr medium

High-intensity optical radiation propagation in a transparent dielectric medium causes the phenomena of pulse self-action and radiation generation at triple frequencies due to the cubic nonlinearity of the medium. However, quadratic nonlinear effects usually outshine the cubic ones in anisotropic nonlinear crystals. In this work, we demonstrate that for certain experimental parameters the nonlinear effect of the third order can be stronger than the second order one in the MgO:hbox {LiNbO}_3 crystal for terahertz frequency range. We experimentally and theoretically show that this effect can lead to the significant modification of the classical phenomenon of radiation generation at triple frequencies in the case when the pulse represents only one complete oscillation of the optical field. The experiment demonstrated that the phenomenon of generation of radiation at triple frequencies with respect to the frequency of the maximum spectral density in a nonlinear medium of the pulse disappears, and it is replaced by the generation of radiation at quadruple frequencies. The analysis confirms that this effect is based on the asymmetry and large width of the initial spectrum of such extremely short pulses in terms of the number of oscillations.

Спектры поглощения пробного сигнала и резонансной флуоресценции для излучателей при их взаимодействии с локальным окружением в прозрачных средах

The current paper demonstrates theoretical analysis of two types of spectral curves for several configurations of system of two-level light emitters, considering the influence of local field and close environment inside a transparent medium. Probe field absorption spectra and resonant fluorescence spectra are calculated under excitation of a strong monochromatic cw laser. The sensitivity of absorption and emission optical spectroscopy method is compared for revealing the effects of the medium on individual emitters and their ensembles. Spectral curves were calculated for model emitters considering local field influence of a transparent dielectric medium and local electron-phonon interactions, which determined the response of the emitters to an external laser field and effective relaxation mechanisms. The calculation formalism is based on a semiclassical approach, while the relaxation processes associated with the phonon contribution are introduced phenomenologically with references to other studies.

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The current paper demonstrates theoretical analysis of two types of spectral curves for several configurations of system of two-level light emitters, considering the influence of local field and close environment inside a transparent medium. Probe field absorption spectra and resonant fluorescence spectra are calculated under excitation of a strong monochromatic cw laser. The sensitivity of absorption and emission optical spectroscopy method is compared for revealing the effects of the medium on individual emitters and their ensembles. Spectral curves were calculated for model emitters considering local field influence of a transparent dielectric medium and local electron-phonon interactions, which determined the response of the emitters to an external laser field and effective relaxation mechanisms. The calculation formalism is based on a semiclassical approach, while the relaxation processes associated with the phonon contribution are introduced phenomenologically with references to other studies.

Investigation of optical resonances arising in the scattered radiation field of a Yb fiber laser in transparent dielectric media

Investigation of optical resonances arising in the scattered radiation field of a Yb fiber laser in transparent dielectric media

Electroabsorption in Metallic Nanoparticles within Transparent Dielectric Media

Electroabsorption in metallic nanoparticles within transparent dielectric media has been measured. In particular, gold nanoparticles in glass and subnanometer-size metallic domains in iodine doped nonconjugated conductive polymer have been studied. Measurements have been made for applied ac fields at 4 kHz, at a wavelength close to the onset of the surface plasmon resonance. The measured electroabsorption (imaginary part of χ(3) or Kerr coefficient) has a quadratic dependence on electric field. Its magnitudes were compared for different sizes of the metallic nanoparticles down to the subnanometer-size particles in iodine-doped nonconjugated conductive polymer. As in the case of quadratic electro-optic effect reported earlier, electroabsorption has approximately a 1/d3 dependence, d being the diameter of nanoparticle. This is consistent with existing theories on confined metallic systems.

Ghost resonance in anisotropic materials: negative refractive index and evanescent field enhancement in lossless media

We show that dielectric waveguides formed by materials with strong optical anisotropy support electromagnetic waves that combine the properties of propagating and evanescent fields. These “ghost waves” are created in tangent bifurcations that “annihilate” pairs of positive- and negative-index modes and represent the optical analogue of the “ghost orbits” in the quantum theory of nonintegrable dynamical systems. Ghost waves can be resonantly coupled to the incident evanescent field, which then grows exponentially through the anisotropic media—as in the case of negative index materials. As ghost waves are supported by transparent dielectric media, the proposed approach to electromagnetic field enhancement is free from the “curse” of material loss that is inherent to conventional negative index composites.

Электромагнитный аналог вытекающей поверхностной упругой волны первого типа для уединенной границы раздела прозрачных диэлектриков

Электромагнитный аналог вытекающей поверхностной упругой волны первого типа для уединенной границы раздела прозрачных диэлектриков

Non-local dispersion and ultrasonic tunneling in concentrationally graded solids

The non-local dispersion of longitudinal ultrasonic waves is shown to appear in the heterogeneous solids due to continuous spatial distributions of their density and/or elasticity (gradient solids). This dispersion gives rise to the diversity of ultrasonic transmittance spectra, including the broadband total reflectance plateau, total transmission and tunneling spectral ranges. The ultrasonic wave fields in gradient solids, formed by interference of forward and backward travelling waves as well as by evanescent and antievanescent modes are examined in the framework of exactly solvable models of media with continuously distributed density and elasticity. Examples of transmittance spectra for both metal and semiconductor gradient structures are presented, and the generality of concept of artificial non-local dispersion for gradient composite materials is considered. It should also be noted that the wave equation for acoustic waves in gradient media with a constant elasticity modulus and a certain predetermined density distribution reduces to an equation describing the electromagnetic wave propagation in transparent dielectric media. This formal similarity shows that the concept of nonlocal dispersion is common for both optical and acoustic phenomena, which opens the way to the direct use of physical concepts and exact mathematical solutions, developed for gradient optics, to solve the corresponding acoustic problems.

Detecting the thermoplasmonic effect using ellipsometry parameters for self-assembled gold nanoparticles within a polydimethylsiloxane matrix

Light-to-heat conversion using active plasmonic materials is essential in wide-ranging applications, such as sensing, photonics, drug delivery, biomedical imaging, photothermal tumor therapy, and optoelectronics. In this work, we studied the thermoplasmonic effect and performed an optical analysis of different concentrations of self-assembled gold nanoparticles in transparent dielectric polydimethylsiloxane polymer medium under continuous-wave radiations. Composite samples were prepared and investigated experimentally by ellipsometry method and thermal photography. The gold-nanoparticle content of each composite film directly increased the generated temperature. The structure and optical properties of the samples under ambient conditions were obtained efficiently depending on the ellipsometry parameters for each polarized light. Results showed that the prolongation of the incubation time led to a lower phase value for p polarization than that for s polarization. This finding was due to the change in ellipsometry parameters and, thus, the thermoplasmonic effect. This new method of investigating the thermoplasmonic effect can provide new insights into the medical applications of plasmonic media.

Cherenkov light imaging in astroparticle physics

Cherenkov light induced by fast charged particles in transparent dielectric media such as air or water is exploited by a variety of experimental techniques to detect and measure extraterrestrial particles impinging on Earth. A selection of detection principles is discussed and corresponding experiments are presented together with breakthrough-results they achieved. Some future developments are highlighted.

Gain of photon-axion conversion in paramagnetics

The possibility of realization of a photon-axion and axion-photon conversion processes in transparent dielectric media within the visible frequency region is analyzed. Materials contain paramagnetic ions with large magnetic moment: Tb3+, Er3+, etc. Therefore an additional strong magnetic field is present in the region of the paramagnetic ion. The reinforced field provides increased probability of the conversion processes. In order to ensure the synchronism condition it is supposed to use laser radiation whose frequency coincides with the frequency of unitary polaritons with a refractive index equals to one. Schemes akin the known scheme “Light Shining through a Wall” can be used to observe the photon-axion conversion process. The estimation of efficiency of conversion processes using real sources of laser radiation and the specific dielectric media with paramagnetic ions is given.

Filament-induced luminescence and supercontinuum generation in undoped, Yb-doped, and Nd-doped YAG crystals

We present a comparative spectral study of filament-induced luminescence and supercontinuum generation in undoped, Yb-doped, and Nd-doped YAG crystals. We show that supercontinuum spectra generated by femtosecond filamentation in undoped and doped YAG crystals are essentially identical in terms of spectral extent. On the other hand, undoped and doped YAG crystals exhibit remarkably different filament-induced luminescence spectra whose qualitative features are independent of the excitation wavelength and provide information on the energy deposition to embedded dopants, impurities, and the crystal lattice itself. Our findings suggest that filament-induced luminescence may serve as a simple and non-destructive tool for spectroscopic studies in various transparent dielectric media.

Nondiffracting and nondispersive vector shovel pulsed beams

Nondiffracting scalar Weber-type parabolic beams are known for their controllable parabolically-shaped transverse profile. They enable a creation of the so-called “optical shovel” beams. We introduce vector parabolic beams and use them to create both nondiffracting and nondispersing femtosecond wave-packets with controllable on-axis polarization structure. Furthermore, we analyze their propagation not only in vacuum but also in a transparent dielectric media (BK7). Here we dive into distortions arising in those beams while applying them for laser-microprocessing applications. We report on successful compensation of those spatio-temporal distortions upon its transmission into bulk of dielectric medium by readjusting angular dispersion of pulse in the air.

Non-local dispersion and ultrasonic tunneling in concentrationally graded solids

The non-local dispersion of longitudinal ultrasonic waves is shown to appear in the heterogeneous solids due to continuous spatial distributions of their density and/or elasticity (gradient solids). This dispersion gives rise to the diversity of ultrasonic transmittance spectra, including the broadband total reflectance plateau, total transmission and tunneling spectral ranges. The ultrasonic wave fields in gradient solids, formed by interference of forward and backward travelling waves as well as by evanescent and antievanescent modes are examined in the framework of exactly solvable models of media with continuously distributed density and elasticity. Examples of transmittance spectra for both metal and semiconductor gradient structures are presented, and the generality of concept of artificial non-local dispersion for gradient composite materials is considered. It should also be noted that the wave equation for acoustic waves in gradient media with a constant elasticity modulus and a certain predetermined density distribution reduces to an equation describing the electromagnetic wave propagation in transparent dielectric media. This formal similarity shows that the concept of non-local dispersion is common for both optical and acoustic phenomena, which opens the way to the direct use of physical concepts and exact mathematical solutions, developed for gradient optics, to solve the corresponding acoustic problems.

New mechanism of surface polariton resonance at an isolated interface between transparent dielectric media (non-Tamm quasistationary surface polariton states)

A pseudochiral mechanism of the formation of non-Tamm quasistationary surface polariton states, as well as surface polariton waves inside the light cone, has been proposed for an isolated interface between spatially uniform transparent dielectric media. The resonance excitation of these states by a quasimonochromatic plane wave incident from vacuum results in a sharp change in the group delay time of the reflected pulse. The effect is enhanced in the presence of an electromagnetic metasurface.

Quantum electron plasma in one-dimensional metallic–dielectric photonic crystal

The interaction of the electromagnetic radiation with one-dimensional photonic crystal consisting of metal and transparent dielectric medium is studied numerically. Dielectric permeabilities of the electron plasma in the metal are considered both in the quantum Mermin and in the classical Drude–Lorentz approaches. It is shown that the reflection, transmission and absorption-frequency zones of electromagnetic radiation appear in the photonic crystal. In addition, the reflectance, transmittance and absorptance optical coefficients for such photonic crystal in the quantum approach differ from those coefficients in the Drude–Lorentz approach.

Visible Light Generated By Short X-ray Pulses

We predict emission of visible or infrared light by ultrashort X-ray pulses moving through a transparent dielectric medium having a visible light index of refraction n(ωL) > 1. The emission occurs if the X-ray pulse is collinear and well-focused. We give reasons to expect that this new type of radiation can be observed on X-ray free-electron laser facilities already beginning operation. The emission is coherent and the intensity is proportional to the square of the number of X-ray photons. The emission spectrum is very sensitive to the X-ray pulse length and that sensitivity may offer a useful new method to measure the X-ray pulse length.

Features of collimation and focusing of few-cycle optical beams

The paper reports theoretical features of collimation and focusing of few-cycle optical beams in transparent isotropic dielectric medium. It was showed, that a spatial collimation of such short waves results in a peculiar shaping of spatio-temporal structure with the central part moving faster than its outlying areas and collimated beam loses with distance half cycle of temporal electromagnetic field oscillation. In focus of focusing mirror, number of oscillations in temporal field structure of beams depends on only temporal profile of radiation source, when focusing collimated wave packet.

Measurements of longitudinal gamma ray distribution using a multichannel fiber-optic Cerenkov radiation sensor

Cerenkov radiation occurs when charged particles are moving faster than the speed of light in a transparent dielectric medium. In optical fibers, Cerenkov radiation can also be generated due to the fiber’s dielectric components. Accordingly, the radiation-induced light signals can be obtained using the optical fibers without any scintillating material. In this study, we fabricated a multichannel, fiber-optic Cerenkov radiation sensor (FOCRS) system using silica optical fibers (SOFs), plastic optical fibers (POFs), an optical spectrometer, multi-anode photomultiplier tubes (MA-PMTs) and a scanning system to measure the light intensities of Cerenkov radiation induced by gamma rays. To evaluate the fading effects in optical fibers, the spectra of Cerenkov radiation generated in the SOFs and POFs were measured based on the irradiation time by using an optical spectrometer. In addition, we measured the longitudinal distribution of gamma rays emitted from the cylindrical type Co-60 source by using MA-PMTs. The result was also compared with the distribution of the electron flux calculated by using the Monte Carlo N-particle transport code (MCNPX).