An efficient multi-domain spectral algorithm for the simulation of dispersive metallic structures in the time domain

In this article, we present a multi-domain formulation of the spectral time domain algorithm for the simulation of dispersive materials. We propose a leap-frog time-stepping scheme similar to the finite-difference time domain method in order to minimize memory usage. Dispersive material behavior is modelled in the frequency domain and used in our time-domain algorithm by introducing auxiliary differential equations for the macroscopic polarization. Absorbing boundary conditions are presented that can be used with dispersive materials. The numerical investigation of structures with material parameters fitted to experimental data shows excellent agreement with theoretical calculations.     

Profile formation in holographic diffraction gratings

A theoretical method is outlined for the calculation of the profiles of holographic diffraction gratings produced in photo-resist. This method is shown to give results in agreement with all experimental observations of such profiles. Consideration is then given to the flexibility of arrangements for the formation of holographic gratings and an experimental system is discussed which fully utilizes this flexibility. The wide range of profiles which may be generated with such a system is demonstrated. Finally a theoretical programme of investigation is suggested which may well make possible the formation of holographic gratings of greatly improved spectral performance.     

Double-layer structural-acoustic coupling for cylindrical shell by using a combination of WDA and BIE

This work formulates the double-layer structural-acoustic coupling problem for cylindrical shell by using a combination of the wave-number domain approach (WDA) and the boundary integral equation (BIE). Expressions for the spectral radial velocity of the outer surface of a finite fluid-filled/submerged (FFS) cylindrical thin shell are formulated by means of the transfer matrix equation in wave-number domain. It is shown that the spectral variables on the inner surface of the shell are related to those on the outer surface of the shell. The far field sound radiation from this kind of shell is numerically evaluated for various fluid cases. An experimental verification is performed, and a good correlation between the theoretical results and the experimental results shows that the theoretical study work in this paper is correct.     

Spectral and polarization analysis of optical images by means of acousto-optics

This paper presents results of a theoretical and experimental study of Bragg anisotropic diffraction. The diffraction may be used for filtration of optical radiation and processing of images. Special attention is devoted to the investigation of diffraction, which provides spectral filtration simultaneously with polarization analysis of divergent optical beams. A tunable tellurium dioxide acousto-optical filter for processing of optical images is described in the paper. Some experimental results of the image analysis in visible light and in the near-infrared region of the spectrum are discussed.     

Theoretical Investigation of Coherent Enhancement for Resonant Two-Photon Transitions

We theoretically investigate the coherent enhancement of resonant two-photon transitions （TPT） in a three-level atomic system. The TPT can be coherently enhanced by modulating spectral amplitude due to eliminating the destructive interference, though partial laser energy losses. Maximal enhancement of TPT can be achieved by modulating spectral phase due to establishing completely constructive interference. Our research provides a theoretical basis for experimental investigation and appears to have potential application on coherent control in the complicated quantum system.     

衍射光栅光谱级数与实验误差的关系研究

从理论上证明了光栅衍射的光谱级数与实验绝对误差的关系,得到二级衍射谱线的精度高于一级衍射谱线的精度,从而能降低实验误差。依据实验数据,计算得到衍射光谱级数不同时的波长,实验结果与理论结论是相吻合的。     

Stimulated Raman spectroscopy using chirped pulses

We present a detailed theoretical and experimental characterization of a new methodology for stimulated Raman spectroscopy using two duplicates of a chirped, broadband laser pulse. Because of the linear variation of laser frequency with time (‘chirp’), when the pulses are delayed relative to one another, there exists a narrow bandwidth, instantaneous frequency difference between them, which, when resonant with a Raman‐active vibration in the sample, generates stimulated Raman gain in one pulse and inverse Raman loss in the other. This method has previously been used for coherent Raman imaging and termed ‘spectral focusing’. Here, gain and loss signals are spectrally resolved, and the spectrally integrated signals are used to determine the spectral resolution of the measured Raman spectrum. Material dispersion is used to generate a range of pulse durations, and it is shown that there is only a small change in the magnitude of the signal and the spectral resolution as the pulse is stretched from 800 to 1800 fs in duration. A quantitative theory of the technique is developed, which reproduces both the magnitude and linewidth of the experimental signals when third‐order dispersion and phase‐matching efficiency are included. The theoretical calculations show that both spectral resolution and signal magnitude are severely hampered by the third‐order dispersion in the laser pulse, and hence, a minimal amount of chirp produces the most signal with only a slight loss of spectral resolution. Copyright © 2014 John Wiley & Sons, Ltd.     

Properties of laser-induced stimulated emission for diagnostic purposes

We describe an experimental and semi-quantitative theoretical investigation of the characteristics of two-photon-induced stimulated emission related to diagnostic applications. The laser power dependence, pressure dependence, and the spectral shape of the stimulated emission signal in CO are discussed and compared with those for laser-induced fluorescence. We also discuss decreases in the laser-induced fluorescence signal caused by the stimulated emission process, and propose a method for providing increased spatial resolution in measurements made using stimulated emission detection.This work was supported by the Swedish National Board for Technical Developments, the Swedish Energy Administration, and the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences     

Modeling of waveguide UV-induced Bragg gratings with arbitrary apodization function: Tools for designing high-performance related devices

We present a semi-analytical modeling suitable for the investigation of the spectral characteristics of UV-waveguide Bragg gratings (UV-WBGs) having arbitrary apodization function and extending both in the film layer and in the overlayer. The modeling is based on a proper combination of coupled mode theory and transfer matrix formalism and provides a powerful tool for designing and simulation of complex UV-grating based structures. The results of a detailed investigation of UV-WBGs in doped silica based channel optical waveguides are presented and critical issues for upgrading the performances of related device are discussed. Validation of the modeling is provided by means of an extensive comparison between theoretical and experimental results relevant to UV-WBGs realized in phosphorous (P)- and boron (B)-doped silica based waveguides.     

The inclusion of source effect consideration in irradiance determination

In optical radiometry, an accurate realization of spectral irradiance scale depends on the investigation of both optical radiation source’s and detecting unit’s (filter radiometer) features. In the source part; comprehensive theoretical and experimental analysis of effects of lamp filament emissivity and its alterations due to the thermal and geometrical factors on the irradiance were studied. Meanwhile, detailed optical characterizations such as; determination of detecting element responsivity, transmittance of filters and measurements of aperture area were also made for the detecting element part. The inclusion of the source effects and the comprehensive theoretical and experimental investigation resulted in the reduction of the number of estimated parameters to be used in matching the theoretical and experimental data, thereby improving the current uncertainty. Moreover, the method we used in this work to analyze the parameters that may affect the irradiance is considered to bring a new approach to the evaluation of irradiance.     

Controlling the propagation of broadband light pulses by Electromagnetically Induced Transparency

We present an experimental and theoretical investigation, performed on hot sodium atoms in a ladder scheme, showing the control of the absorption and of the propagation velocity of a probe light pulse with a spectral bandwidth as large as 1.8 GHz. The predictions of the theoretical model compare favorably with the experimental results.     

不同观察者锥细胞响应的同色异谱性能差异测试分析

为了研究不同年龄色觉正常观察者在不同观察条件下的锥细胞光谱响应差异,在CIELAB颜色空间选择了均匀分布的9个不同色调的颜色,组织27～35名观察者开展了两种不同光源照度和两种不同观察视场的四种观察条件下,基于显示色-打印色的颜色匹配实验。通过配色实验采集到不同观察者匹配颜色的光谱数据,与9个目标色的光谱数据计算、比较,以匹配的9个颜色最小平均CIEDE2000色差值出现的概率大小作为评价标准,检验CIE1931,CIE1964,CIE2006,Sarkar(S1～S8)共11种颜色匹配函数的表现,研究不同观察者锥细胞响应的同色异谱性。结果表明在四种不同实验条件下,表现最好的配色函数依次是CIE2006,S6,表现最差的是S1和S2。不同观察者的锥细胞响应同色异谱性差异较大,年龄因素对观察者的锥细胞响应的影响也较为明显。(λ)通道的光谱响应差异是造成不同观察者存在同色异谱现象的主要原因,大多数观察者的差异性主要集中在(λ)通道的峰值波长响应,峰值波长的位移对颜色匹配的结果影响不大。实验结果可为进一步划分不同观察者的颜色匹配函数,研究不同观察者的同色异谱性提供数据支持和理论依据。     

Neutron resonances in planar waveguides

We report on the results of the experimental investigation of the spectral width of neutron resonances in planar waveguides using the time-of-flight method and recording the microbeam emerging from the waveguide end. Experimental data are compared with the results of theoretical calculations.     

A method for the rapid evaluation of critical multiple scattering

Simple analytic formulas are derived for the double scattering to single scattering ratio near the critical point of a fluid. They are valid even close to the critical temperature, where turbidity is important, and concern right-angle scattering from a roughly cubic sample. New experimental results for the binary mixture nitrobenzene-n-hexane, as well as previously published results for 4 critical fluids are in good agreement (±20%) with our theoretical predictions. The order of magnitude for the ratio of spectral intensities is also estimated.     

On the amplified spontaneous emission noise modeling of semiconductor optical amplifiers

We perform a theoretical investigation of two modeling approaches for the amplified spontaneous emission (ASE) noise of a semiconductor optical amplifier (SOA), namely a stochastic time-domain and a deterministic frequency-domain approach. The theoretical results are compared to one another having as reference experimental measurements obtained from a commercial device. Special emphasis is placed on the modeling of the material gain as it is a key parameter in determining the ASE spectral characteristics. A comprehensive set of equations for both modeling approaches is developed and their numerical solution is analyzed in detail.     

Quasioptical multilayered interferometer for gasoline testing

Results of an experimental study and a calculation of the quasi-optical multilayered structure formed by an adjustable dielectric interferometer and a liquid investigated filling its gabs are presented. It is shown that this structure may be used for quality tests of liquid petroleum products, for measurement and investigation of physical parameters of liquid media in the millimeter wavelengths region. This structure is realized practically in the form of uncomplicated adjustable quazi-optical quvette filled with liquid and connected with beam-guiding elements. Comparison of experimental data with theoretical calculations gives us the opportunity to choose a value region of the values for the physical parameters interesting for us for each material under investigation.     

The influence of scanning rate in sequential analysis of fringes produced by a Michelson interferometer

The influence of sequential analysis rate on measurements of Michelson fringes is examined on a theoretical basis, sh whilst considering the special case where the elementary telescope pupils are small in comparison with Fried's parameter (r₀). As a result of this investigation it seems that the principal effect due to an insufficient scanning rate is a degradation of the spectral analysis window employed in the calculation of spatial energy spectra. This effect is related to Fried's parameter and to the wind speed. Taylor's hypothesis is employed in the calculation.The results obtained appear to be consistent with experimental observations.     

Wander of a Gaussian-Beam Wave Propagated Through a Non-Kolmogorov Turbulent Atmosphere

Both increasing experimental evidence and some results of theoretical investigation have shown that there exist two kinds of turbulence in the aerosphere, Kolmogorov and non-Kolmogorov turbulence. Thus, it is necessary to improve the theory of optical wave propagation through atmospheric turbulence, namely, study the laser-beam propagation in non-Kolmogorov turbulence, before analyzing the joint influence of the Kolmogorov turbulence and non-Kolmogorov one on satellite laser communication. The beam wander will lead to the performance degradation of satellite laser communication systems and exert an influence on the achievement and stability of its links. In this paper, we consider a theoretical power spectrum of refractive-index fluctuations with a generalized power law in order to derive the variance of Gaussian-beam wave wander in weak turbulence for a horizonal path and analyze the influence of spectral power-law variations on the beam wander. We show that the expression for the beam-wander variance is of concise closed form and independent of the optical wavelength.     

Continuous radiation from a dense,weakly non-ideal,argon plasma

Continuum radiation from the argon plasma generated by a cascade arc has been investigated over the pressure range 1–10 atm and the temperature range 12?16×10³⁰K in the visible, near i.r. and u.v. spectral regions. Plasma temperatures were found from absolute intensities of the argon atom and ion lines; the concentrations of charged particles were determined from the ion-line half-widths.The results obtained on the continuum radiation intensity are compared with theoretical and experimental data obtained by other authors. At elevated pressures, the experimental data have been found to exceed theoretical values in the spectral region under investigation. The dependence of the recombination-threshold-shift in the plasma on azimuthal quantum number appears to be worthy of special attention. Possible reasons for excess radiation are discussed.     

Estimation and correction of the influence of an IR spectometer on mechanical vibrations

The problem of influence of mechanical vibrations on a measurement is well known and analyzed for ground conditions. However, the problem becomes quite essential and difficult to solve in space conditions. The influence of vibrations on accuracy of the measurement was observed on MIPAS – ENVISAT and in PFS Mars Express.This paper presents an experimental and theoretical investigation on sensitivity to mechanical disturbances of the Fourier-transform infrared spectrometer PFS.A theoretical analysis has been performed in order to highlight the expected effect of the vibration, then laboratory tests have been designed and carried out for instrument characterization.The theoretical investigation has been confirmed by experimental tests.The data were distorted by errors that reflect the influence of vibrations on the instrument and temperature instability of the reference source.The considerations are a perfect example presenting the scale of vibrations problem and the instability of the reference source in assessing accuracy of the measurement in space.