Far infrared radiation generated during femtosecond laser excitation of a semiconductor surface in magnetic field

The effect of a magnetic field on the generation of electromagnetic radiation pulses in the terahertz frequency range from a semiconductor surface excited by an ultrashort laser pulse is considered within the framework of a hydrodynamic model. The appearance of a photocurrent component in the Hall direction leads to elliptic polarization of the microwave radiation and to a severalfold increase in the generation efficiency. This is consistent with the results of Monte Carlo modeling of a self-consistent field and photogenerated carrier dynamics.     

Far field of gratings with rough strips

In this work, we analyze the far-field pattern produced by a grating made of strips with two different random roughness levels. The efficiency and shape of the diffraction orders is obtained, which are shown to depend on the statistical properties of roughness. We assume for the calculations that the grating can be used in a mobile mechanical system. A preliminary experimental approach which partially corroborates the theoretical results is also performed.     

On temperature determination of opaque materials through the spectral maximum of thermal radiation

For the thermal radiation spectral maximum of an opaque freely radiating body, an equation relating the wavelength, the emissivity, and the thermodynamic (the true) temperature of the body is derived. Also a nondimensional parameter bounding the emissivity, its derivative, and the wavelength is identified in the radiation spectral maximum. A value range of this parameter where use of the obtained equation reduces the required temperature uncertainty is determined. Furthermore, a dimensionless parameter characterizing the deviation of the thermal radiation of the real materials from the Wien displacement law is found. The interconnection of the obtained parameters is revealed. By means of a computer experiment, it is shown that, for selectively radiating materials such as tungsten at 2600–3000 K, determination of the true temperature according to the Wien displacement law results in deviations from the true temperature by more than 200 K.     

Generalized beam-propagation factor of partially coherent beams propagating through hard-edged apertures

The second-order intensity moments and beam-propagation factor (M2 factor) of partially coherent beams have been generalized to include the case of hard-edged diffraction. A laser beam with amplitude modulation and phase fluctuation and a Gaussian Schell-model beam are taken as two typical examples of partially coherent beams. Analytical expressions for the generalized M2 factor are derived.     

Extraordinary terahertz transmission through a copper film perforated with circular and rectangular apertures

The extraordinary transmission (ET) due to localized surface plasmon (LSP) and propagating surface plasmon (PSP) resonances of terahertz wave through a copper film perforated with circular and rectangular apertures is investigated theoretically and experimentally. Considering that the field distributions of LSP and PSP resonances are determined by the shape and periods of the apertures on the film, the relations between extraordinary and the geometrical parameters of the apertures are investigated. The intensities of the ETs induced by the PSP resonances mode [1, 1] are much stronger than the fundamental ones [1, 0] and [0, 1]. Our finds provide another effective method to tailor the extraordinary THz transmission in sub-wavelength metallic aperture structures.     

Alanine blends for ESR measurements of thermal neutron fluence in a mixed radiation field

In this paper, the results of a study on the electron spin resonance (ESR) dosimetry to measure thermal neutron fluence in a mixed radiation field (neutron and photons) are presented. The ESR responses of alanine dosemeters with different additives are compared. In particular, the (10)B-acid boric and the Gd-oxide were chosen to enhance the sensitivity of alanine dosemeters to thermal neutrons. Irradiations were carried out inside the thermal column of the TAPIRO reactor of the ENEA center, Casaccia Rome. The main results are a greater neutron sensitivity and a smaller lowest detectable fluence for the dosemeters with gadolinium than for dosemeters of alanine with (10)B, which is well known to be much more sensitive to thermal neutrons than simple alanine.     

Surface-enhanced Raman scattering on gold nanotrenches and nanoholes

Dependent effects on edge-to-edge distance and incidence polarization in surface-enhanced Raman Scattering (SERS) were studied in detection of 4-mercaptopyridine (4-MPy) molecules absorbed on gold nanotrenches and nanoholes. The gold nanostructures with controllable size and period were fabricated using electron-beam lithography. Large SERS enhancement in detection of 4-MPy molecules on both nanostructred substrates was observed. The SERS enhancement increased exponentially with decrease of edge-to-edge distance for both the nanotrenches and nanoholes while keeping the sizes of the nanotrenches and nanoholes unchanged. Investigation of polarization dependence showed that the SERS enhancement of nanotrenches was much more sensitive to the incidence polarizations than that of nanoholes.     

Transmission through single subwavelength apertures in thin metal films and effects of surface plasmons

The existing analyses on extraordinary optical transmission through apertures on a metal screen have been carried out assuming perfect conductivity or by examining arrays of closely spaced holes with subwavelength dimensions. We present an electromagnetic analysis of a single hole (modeled by use of an array of distant holes) in a finitely conducting metal membrane, applying no approximations. We demonstrate that finite conductivity is not of remarkable importance with small hole-diameter-to-wavelength ratios in the absence of strong resonances. However, if the angle of incidence of a plane wave is such that surface plasmons are excited, substantial enhancement of the transmittance can be observed, and the effect of finite conductivity will no longer be negligible. Our analysis also reveals that transmission of small apertures in highly conducting membranes can be described by approximate analytical formulas if surface waves are not excited, but with poor conductors the full electromagnetic analysis should be applied.     

Diffraction of transmission light through triangular apertures in array of retro-reflective microprisms

An array of microprisms was described by a model of multiperiod blazed gratings consisting of triangular apertures. The origins of hexagram-shaped diffraction patterns were interpreted based on multiple-beam interference and diffraction array theorem. The relation between zonal/line ghost fringes and imperfectly fabricated array structures was analyzed. Geometrical performance (e.g., the dihedral angle of the microprism) was tested by measuring the features of diffraction patterns of samples from three retroreflective sheeting manufacturers.     

Influence of thermal radiation on the structure of the temperature field in a turbulent flow

The form of the structural function for temperature fluctuations in the turbulent flow of a radiation gas is set up theoretically.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 5, pp. 773–780, November, 1985.     

Modeling of explosion thermal radiation

The hydrodynamic and radiation processes accompanying explosions of chemical explosives and fuel-air mixtures have been considered. Computer modeling of the radiation from a fire ball of explosion and a flame of diffusion combustion of a hydrocarbon fuel has been performed. The dependences of the heat flux density from the region occupied by explosion and combustion products on its temperature and geometric characteristics have been determined. Thermal load distributions on targets of different orientations in the vicinity of the energy release zone have been obtained. A comparison of the thermal parameters on radiation detectors with the criteria of thermal affection of people and ignition of combustible materials has been made.     

Natural thermal radiation of heat-absorbing thermal vacuum chamber shields

A simplified method for computing the natural thermal radiation of heat-absorbing shields of vacuum chambers is elucidated; computational dependences are presented for shields of herringbone outlines and the influence of the geometric profile characteristics on the magnitude of the natural radiation is shown.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 2, pp. 317–321, February, 1976.     

Far field intensity of a partially locked optical phased array

The effects of imperfect frequency locking on the performance of an optical phased array were investigated. An analytic expression was obtained for the far field intensity pattern in terms of the degree of mutual coherence between lasers. The results of the analytical study were applied to determine the Strehl ratio of an injection coupled optical phased array for different degrees of slave resonator length control, ratios of injected to slave laser intensities, and pulse durations.     

Temperature fields in thermal radiation detectors

Results of analysis of thermal processes in a superconducting thermal radiation detector, formulated as a boundary-value problem of complicated heat transfer in a three-dimensional region of complex geometry, are reported. Variants of the problem for simplification are given; the limitations of these assumptions are pointed out.Khar'kov Aviation Institute. Translated from Inzhenerno-Fizicheskii zhurnal, Vol. 64, No. 2, pp. 228–232, February, 1993.     

Particle states of the radiation field

Quantum states of the radiation field for free, propagating electromagnetic waves are well known to be quantized solutions of the D'Alembertian operator which represent free photons. In this paper anti-propagating solutions of the D'Alembertian are found which decay exponentially spatially and grow exponentially temporally. These states are simply related to standing-wave solutions of the D'Alembertian which are analytically continued to the imaginary momentum axis. The temporally growing solutions are bounded by the Lorentz invariance of the squared four-position c ² t²???r²?=?0, in which the radial position r is bounded by the anti-propagating nature of the solution. Stationary solutions are found from a linear combination of squared scalar potentials. A pair of physically interesting results, the electric charge and the fine structure constant, are inferred from the normalized and quantized stationary scalar potential.     

Measurement and control of thermal radiation below 6K

The power absorbed by a surface at 0.2 K illuminated with thermal radiation from a surface at 0.9–6 K has been measured using a variety of materials for these surfaces. Also, the reduction in the absorbed power by the insertion of various thermal shields has been measured. The results are compared with theory and with other measurements. Conclusions as to appropriate design techniques for cryogenic apparatus are discussed.This work was supported in part by the Advanced Research Projects Agency under Contract HC 15-67-C-0221.