Passage of monochromatic radiation through a resonance radiation absorbing medium

The problem of passage of monochromatic radiation pulses through a one-dimensional medium containing several types of nonuniformly distributed absorption centers with coincident energy levels are considered. The physical picture associated with the effect of a brightening wave arising in an optically dense absorbing medium is analyzed. The investigated relations represent a generalization of Bouguer's law for the case of powerful fluxes of monochromatic radiation with allowance for absorption saturation.     

Transient radiation and conduction heat transfer inside a plane-parallel participating gray medium with boundaries having different reflecting characteristics

A hybrid ray-tracing method is developed for the solution to the radiative transfer in a plane-parallel participating medium having one specular surface and another diffuse surface. By this method, radiative transfer coefficients (RTCs) for specular–diffuse (S–D) surfaces are deduced. The medium surfaces are considered to be semitransparent. The effects of convection–radiation parameter, conduction–radiation parameter and refractive index on transient coupled heat transfer are investigated. Results show that the temperature curves of the medium having S–D surfaces is higher than those of the medium having S–S surfaces (two specular surfaces); the total heat flux at steady state for the S–D surfaces is lower than that for the S–S surfaces.     

Radiative transfer in a scattering medium with angle-dependent reflective boundaries

Abstract

Radiative transfer in an anisotropically scattering slab with direction-dependent reflectivities at the interfaces is solved using the Pomraning–Eddington variational method. The interfaces are assumed to reflect specularly as a function of angle of incidence according to Fresnel's equation. The quantities of interest, such as the hemispherical reflectivity and transmissivity of the medium, are calculated for different optical thicknesses, single-scattering albedos and refractive indices of the medium. The results are compared with the exact numerical results and with those obtained using the average value of the reflectivities instead of the angle-dependent Fresnel reflectivity. Calculations are also performed for a semi-infinite medium and compared with results calculated using the average reflectivities.     

The parametric Doppler effect in a medium with Lorentz dispersion

The frequency conversion under the parametric Doppler effect, which occurs when weak probe radiation reflects off from a refractive index inhomogeneity induced in a nonlinear medium by intense pumping, has been analyzed. Under these conditions, the frequency dispersion of the medium is assumed to correspond to the single Lorentz oscillator model. It is shown that the presence of resonance and a spectral range forbidden for propagation may lead to a complex Doppler effect, where the incident radiation is single-frequency but the reflected radiation consists of two or three monochromatic waves, one of which has a phaseconjugated wavefront.     

Radiative heat transfer in a planar medium with anisotropic scattering and directional boundaries

Radiation heat transfer in an absorbing, emitting and scattering medium has been the subject of many previous investigations. Most solutions are numerically complex and the existing analytical solutions are restricted in application by the simplifying assumptions involved. A plane-parallel medium is considered which scatters anisotropically. The boundaries are considered to be specular reflectors, as predicted by Fresnel's relations, while the diffusely incident radiation is refracted according to Snell's law. The emission is restricted to a medium with a uniform temperature distribution. Approximate closed-form solutions for the radiative heat flux and incident intensity are presented for dielectric layers and linear anisotropic scattering. Numerical results are also presented and show that the effects of directional boundaries, anisotropic scattering, scattering albedo and optical depth are accurately predicted by the approximate solution.     

The effect of longitudinal-transverse coupling and medium temperature on Cerenkov radiation

The effect of medium properties on the energy loss suffered by a relativistic charged particle in a dielectric medium generating Cerenkov radiation is discussed. Here we have taken into account the effect of the coupling of the longitudinal (σ) mode with the transverse (λ) mode in the electromagnetic interaction. Calculation shows that the inclusion of λ-σ coupling in the transverse interaction affects significantly the radiation output. However the modification of the radiation due to the thermal state of the system becomes important at very high temperatures such as one finds in astrophysical situations. This temperature effect is negligible at ordinary temperatures and thus is undetectable in laboratory experiments.     

Wave diffraction on an infinite chaotic screen bounding a medium with spatial and time dispersion

Electromagnetic wave diffraction on a chaotic screen, bounding a medium with time and spatial dispersion, has been investigated. The longitudinal and cross-correlation functions of waves in the limit cases of the correlation radius being longer or shorter than the wavelength have been evaluated. This letter considers the radiation of a plane antenna with dimensions much larger than the wavelength and with arbitrary current distribution on the surface; the antenna radiates into dielectric half-space with spatial and time dispersion.     

材料色散对LPFG双峰谐振效应特性的影响

采用严格的耦合理论,研究了长周期光纤光栅各层材料色散对双峰谐振效应的影响,指出芯层和包层材料色散必须同时考虑才能切实地符合实际情况.分析了材料色散对不同膜层参数下双峰谐振LPFG透射特性的影响,模拟计算了材料色散计及与否时的双峰谐振波长,两种情形下两峰偏差值分别约在1.5—2 nm和6.5—7.5 nm浮动.最后,讨论了材料色散对双峰LPFG传感器灵敏度的影响.结果表明,此类传感器对膜层折射率的分辩率高达10^-8,计及材料色散后的等高线图可为传感器灵敏度设计提供精确的参数选择组合. 关键词： 材料色散 长周期光纤光栅 双峰谐振     

Heat transfer in a spherical turbid medium with conduction and radiation

The heat transfer through a spherical media with conduction and radiation is considered. The medium is considered to be turbid and anisotropically scattering with diffusely reflecting boundaries of constant temperatures. The radiative transfer problem is solved using the Galerkin method. An iterative method is used to solve the nonlinear relation between the radiative transfer equation and the conductive energy equation. Calculations are carried out and compared for a homogeneous, isotropically scattering medium with isothermal, transparent boundaries. The results show good agreement with previous work. Calculations are carried out for inhomogeneous media with isotropic, and forward and backward anisotropic scattering. The boundaries of the media are considered to be isothermal and may be transparent or diffusely reflecting boundaries. The calculations are used to study the effects of the single scattering albedo, the anisotropic scattering parameter, the conduction-radiation parameter and the heat source.     

The effect of self-absorption on cyclotron resonance radiation in semiconductors

Every non-two body interaction does not lead to a violation of the Cauchy symmetry in elastic constants. The condition forM-body interaction to satisfy Cauchy symmetry is discussed. For this purpose a simple expression for the contribution to the Brugger elastic constants in terms of theM-body force constants is derived. The advantage of the expression is that the force constants have to satisfy only the rotational and translational invariance conditions but not the equilibrium conditions.     

Emission of radiation by a resonance medium excited with a variable superluminal velocity

Specific properties of the radiation emitted by a spatially modulated resonance medium excited by an ultrashort light pulse propagating through the medium at a variable superluminal velocity are analyzed. In so doing, frequencies different from that of the resonance transition of the medium may appear in the emission spectrum. It is demonstrated that, in contrast to an earlier studied case of medium excitation at constant velocity, variation of the excitation velocity leads to generation of a spectral continuum, the boundaries of which are determined by the range of variation of the medium-excitation velocity.     

The Iterative-DRESOR method to solve radiative transfer in a plane-parallel, anisotropic scattering medium with specular-diffuse boundaries

Using the intensity with high directional resolution obtained by the Basic-DRESOR method as an initial guess, which is substituted into the integrated radiative transfer equation (IRTE), an iterative algorithm is proposed, called the Iterative-DRESOR method. This method can reduce the error levels of the intensity from several percent using the Basic-DRESOR method to a level of less than 1.0×10⁻⁶ with acceptable computation costs. The method is also validated against the exact heat flux in literature in some cases. It further clarifies some uncertain results for the reflectance in a pure, linearly anisotropic scattering medium with specular-diffuse boundaries. The directional distributions of intensity are obviously influenced by the reflecting modes of the boundary, especially in the zone near the boundary. The reflecting mode of an emitting boundary has little effect on the transmittance or reflectance. The reflecting mode of a non-emitting boundary also has little effect on the transmittance, but it obviously influences the reflectance. The difference between the reflectance for specular and diffuse boundaries increases at first, and then decreases, as the optical thickness of the medium increases. The difference will decrease as the scattering albedo of the medium increases, and it is negligible when the medium is pure scattering. The effect of the scattering phase function of the medium on the difference can also not be ignored. The Iterative-DRESOR method is expected to strengthen the capability of the Monte Carlo method to produce accurate results and to validate the results of other methods to solve RTE.     

Statistical properties of resonance radiation selectively reflected from a cold semi-infinite medium

The problem of the quantum-statistical properties of resonance radiation selectively reflected from unexcited media in the case where the photons are mutually correlated in the incident radiation flux is posed and solved. Allowance for mutual photon correlation precludes, in principle, solving the problem by perturbation methods. A quantum analog of the optical theorem of absorption, which causes an infinite subsequence of Feynman diagrams to vanish, is pointed out. The frequency-angle distribution of the photons in the reflected flux is predicted. The Fresnel formulas are reconstructed for the averaged reflection characteristics. The limits for their applicability in describing the reflection of mutually correlated photons are given. A suppression effect is predicted for the reflection of radiation from a laser source. Zh. éksp. Teor. Fiz. 116, 821–837 (September 1999)     

The effect of metal dispersion on the resonance of antennas at infrared frequencies

In this paper the optical parameters at infrared frequencies of metallic thin films were obtained experimentally using a variable angle spectroscopic ellipsometer and used to simulate numerically the frequency response of antennas and antenna-coupled detectors at infrared frequencies (5–15 μm). The simulation results agree with previously published data and practical guidelines are presented for the design and fabrication of dipole and bowtie antennas at infrared frequencies.     

Time-dependent radiation transfer in a semi-infinite stochastic medium with Rayleigh scattering

The time-dependent radiation transfer in a semi-infinite stochastic medium of binary Markovian mixture with Rayleigh scattering is presented. A formalism, developed to treat radiation transfer in statistical mixtures, is used to obtain the ensemble-averaged solution. The average reflectivity, radiant energy and net flux are computed for specular-reflecting boundary. For the sake of comparison, we use two different weight functions in our calculations.