Spectral Intensity Distribution Research Articles

Determination of Opaque Material Temperature from the Spectral Distribution of Emitted Radiation Intensity with Unknown Emissivity

The thermodynamic temperature of an opaque material with unknown emissivity was determined from the recorded distribution of spectral intensities of the emitted radiation. The initial system of equations was derived in the logarithmic form in accordance with the Planck formula. At the first stage, the spectral dependence of the material emissivity was investigated with a special function—relative emissivity. Based on the analysis of spectral dependences of this function at different reference temperatures, a parametric model for the material emissivity was chosen. At the second stage, the desired parameters of the chosen model of spectral emissivity and the thermodynamic temperature of the material were determined. An example of the determination of a temperature of a tungsten sample from the spectral distribution of emitted radiation intensities is given. A method for narrowing the range, which includes the thermodynamic temperature of the material, is presented.

Multiple nonlinear Bragg diffraction of femtosecond laser pulses in a photonic lattice with hexagonal domains

The frequency doubling of femtosecond laser pulses in a two-dimensional (2D) rectangular nonlinear photonic lattice with hexagonal domains is studied experimentally and theoretically. The broad fundamental spectrum enables frequency conversion under nonlinear Bragg diffraction for a series of transverse orders at a fixed longitudinal quasi-phase-matching order. The consistent nonstationary theory of the frequency doubling of femtosecond laser pulses is developed using the representation based on the reciprocal lattice of the structure. The calculated spatial distribution of the second-harmonic spectral intensity agrees well with the experimental data. The condition for multiple nonlinear Bragg diffraction in a 2D nonlinear photonic lattice is offered. The hexagonal shape of the domains contributes to multibeam second harmonic excitation. The maximum conversion efficiency for a series of transverse orders in the range 0.01%–0.03% is obtained.

Transition radiation on a superlattice in finite thickness plate generated by two acoustic waves

Forward transition radiation from relativistic electrons is investigated in an ultrasonic superlattice excited in a finite thickness plate by two acoustic waves. In the quasi-classical approximation formulae are derived for the vector potential of the electromagnetic field and for the spectral-angular distribution of the radiation intensity. Zone structures appear in the plate, which makes it possible (by an appropriate choice of the frequencies of the two acoustic waves) to control the spectral-angular distribution of the radiation through changes in the parameters of the medium. The acoustic waves generate new resonance peaks in the spectral and angular distribution of the radiation intensity. The heights of the peaks can be tuned by choosing the parameters of the acoustic waves. Numerical examples are presented for a plate of fused quartz.

Angle-resolved spectral Fabry–Pérot interferometer for single-shot measurement of refractive index dispersion over a broadband spectrum

An angle-resolved spectral Fabry–Pérot interferometer is reported for fast and accurate measurement of the refractive index dispersion of optical materials with parallel plate shape. The light sheet from the wavelength tunable laser is incident on the parallel plate with converging angles. The transmitted interference light for each angle is dispersed and captured by a 2D sensor, in which the rows and the columns are used to simultaneously record the intensities as a function of wavelength and incident angle, respectively. The interferogram, named angle-resolved spectral intensity distribution, is analyzed by fitting the phase information instead of finding the fringe peak locations that present periodic ambiguity. The refractive index dispersion and the physical thickness can be then retrieved from a single-shot interferogram within 18 s. Experimental results of an optical substrate standard indicate that the accuracy of the refractive index dispersion is less than 2.5 × 10−5 and the relative uncertainty of the thickness is 6 × 10−5 mm (3σ) due to the high stability and the single-shot measurement of the proposed system.

A dish-type high-concentration photovoltaic system with spectral beam-splitting for crop growth

Photovoltaic (PV) systems are playing a more and more important role as a renewable energy supplier. However, their large-scale applications is still limited by low conversion efficiency and high land-use requirement, especially for those areas where land and solar energy resources are more important for agriculture. In this paper, we suggest a dish-type high-concentration photovoltaic system, with which the competition between sunlight for crops' growth and PV application is solved by beam-splitting techniques. A purposely-designed beam filter acts as a solar spectrum splitter, and the most effective bands of solar spectrum for plant growth are transmitted down to plants while the other parts are all directed to the solar cell receiver. The spectral and spatial distribution of radiant intensity is investigated by ray tracing method, and the quantitative evaluation of the beam splitting effect on crop growth and PV power generation is provided in detail. The results show that, on one hand, the proposed system is superior to other natural and artificial light sources at driving the photosynthetic process (thus promoting crop growth); on the other hand, it generates PV power with high efficiency. Furthermore, the design can be optimized for certain kinds of plants and PV generation, both or independently. This spectral splitting scheme opens a promising future for PV applications in cooperation with precision farming.

Pulsed single-photon spectrometer by frequency-to-time mapping using chirped fiber Bragg gratings.

A fiber-integrated spectrometer for single-photon pulses outside the telecommunications wavelength range based upon frequency-to-time mapping, implemented by chromatic group delay dispersion (GDD), and precise temporally-resolved single-photon counting, is presented. A chirped fiber Bragg grating provides low-loss GDD, mapping the frequency distribution of an input pulse onto the temporal envelope of the output pulse. Time-resolved detection with fast single-photon-counting modules enables monitoring of a wavelength range from 825 nm to 835 nm with nearly uniform efficiency at 55 pm resolution (24 GHz at 830 nm). To demonstrate the versatility of this technique, spectral interference of heralded single photons and the joint spectral intensity distribution of a photon-pair source are measured. This approach to single-photon-level spectral measurements provides a route to realize applications of time-frequency quantum optics at visible and near-infrared wavelengths, where multiple spectral channels must be simultaneously monitored.

Quantum-mechanical calculation of the intensity distribution in Raman and resonance Raman spectra of a phenylalanine aqueous solution

Quantum-mechanical calculations of the intensity distribution in the resonance Raman spectrum of an aqueous solution of phenylalanine, excited by light with wavelengths of 193, 204, 218, and 235 nm, and in the nonresonant Raman spectrum excited at a wavelength of 488 nm have been performed. The calculation results are in satisfactory agreement with the experimental data in the literature. Spectral lines characteristic of phenylalanine are observed, which can be used as markers when analyzing the peptide structure. It is noted that the contribution of highly excited electronic states (spaced by less than 10 eV from the resonant lines) to the scattering tensor components must be taken into account. The important role of the Herzberg–Teller effect in the description of spectral intensity distribution is demonstrated.

Propagation of stochastic electromagnetic high-order Bessel-Gaussian beams in the oceanic turbulence

Recently, the laser beam propagation in the oceanic turbulence has become a hot research topic. In addition to the characteristics of free diffraction and self-reconstruction, the high-order Bessel-Gaussian beam is a kind of typical vortex beam because of the existence of a spiral phase factor with orbital angular momentum. Researchers have investigated the self-reconstruction property of the high-order Bessel-Gaussian beams in the free space, also carried out intensive researches on the transmission characteristics of high-order Bessel-Gaussian beam in the ABCD optical system and in the atmospheric turbulence. However, to the best of our knowledge, to date there has been no investigation on the propagation of this laser beam in the oceanic turbulence. In this paper, we will study the propagation characteristics of the random electromagnetic high-order Bessel-Gaussian beams in the oceanic turbulence, and discuss the variation of the normalized spectrum intensity, the spectral degree of polarization, and the spectral degree of coherence. By using the extended Huygens-Fresnel diffraction integral formula, the general expression for the cross spectral density matrix of the stochastic electromagnetic high-order Bessel-Gaussian beams propagating in the oceanic turbulence is obtained, and the statistical properties of the random electromagnetic high-order Bessel-Gaussian beams propagating in the seawater are investigated by numerical calculation. The numerical results show that the oceanic turbulence can affect the normalized spectral intensity distribution of the random electromagnetic beam. With the increase of the transmission distance, the center of the zero-order Bessel-Gaussian beam becomes depressed, and the center of the higher-order Bessel-Gaussian beam will become flat and then depressed. As the transmission distance increases far enough, regardless of the zero-order or higher-order, the intensity distribution will eventually evolve into the quasi Gaussian shaped distribution. The variation of the degree of polarization of each point on the x axis is related to the coherence length (xx，yy) and the oceanic turbulence parameters. The spectral coherence of the origin and any point on the x axis also changes with the increase of x, and the rate of dissipation of mean-square temperature T has influence on the spectral coherence. This research is of great value for applying the high-order Bessel-Gaussian beam to the optical communication, optical imaging and underwater exploration in the ocean.

Tuning the Electronic Structure and Properties of Perylene-Porphyrin-Perylene Panchromatic Absorbers.

Light-harvesting architectures that afford strong absorption across the near-ultraviolet to near-infrared region, namely, panchromatic absorptivity, are potentially valuable for capturing the broad spectral distribution of sunlight. One previously reported triad consisting of two perylene monoimides strongly coupled to a free base porphyrin via ethyne linkers (FbT) shows panchromatic absorption together with a porphyrin-like S1 excited state albeit at lower energy than that of a typical monomeric porphyrin. Here, two new porphyrin-bis(perylene) triads have been prepared wherein the porphyrin bears two pentafluorophenyl substituents. The porphyrin is in the free base (FbT-F) or zinc chelate (ZnT-F) forms. The zinc chelate (ZnT) of the original triad bearing nonfluorinated aryl rings also was prepared. The triads were characterized using static and time-resolved optical spectroscopy. The results were analyzed with the aid of molecular-orbital characteristics obtained using density functional theory calculations. Of the four triads, FbT is the most panchromatic in affording the most even distribution of absorption spectral intensity as well as exhibiting the largest wavelength span (380-750 nm). The triads exhibit fluorescence yields (0.35 for FbT-F in toluene) that are substantially greater than for the porphyrin benchmarks (0.049 for FbP-F). The singlet excited-state lifetimes (τS) for the triads in toluene decrease in the order FbT-F (2.7 ns) > FbT (2.0 ns) > ZnT (1.2 ns) ∼ ZnT-F (1.1 ns). The τS values in benzonitrile are FbT (1.3 ns) > FbT-F (1.2 ns) > ZnT-F (0.6 ns) > ZnT (0.2 ns). Thus, the free base triads exhibit relatively long (1.2-2.7 ns) excited-state lifetimes in both polar and nonpolar media. The combined photophysical characteristics indicate that FbT and FbT-F are the best choices for panchromatic light-harvesting systems. Collectively, the findings afford insights into the effects of electronic structure on the panchromatic behavior of ethynyl-linked porphyrin-perylene architectures that can help guide next-generation designs and utilization of these systems.

Temperature sensitivity of molecular oxygen resonant-enhanced multiphoton ionization spectra involving the C 3Π g intermediate state

The technique of measuring O2 rotational temperature by coherent microwave Rayleigh scattering from resonance-enhanced multiphoton ionization (Radar REMPI) has been studied to determine temperature sensitivity and range. The molecular oxygen Rydberg state of \(\left( {3s\sigma } \right)C{{}^{3}}\Pi_{g} \left( {v^{\prime } = 2} \right)\) has been selected as the intermediate state in the 2 + 1 REMPI process, which is known to provide a relatively strong REMPI signal. Rotational-resolved spectra representing the two-photon \(C{{}^{3}}\Pi_{g} \left( {v^{\prime } = 2} \right) \leftarrow \leftarrow X{{}^{3}}\varSigma _{g}^{ - } \left( {v^{\prime \prime } = 0} \right)\) transition have been obtained under several gas conditions including pure oxygen, air-like syngas, ambient air, and flame environments from room temperature (~300 K) to flame temperature (~1700 K). An O2 REMPI spectral model has been developed to simulate the experimental spectral line intensity distribution which is dependent on the O2 ground-state temperature. The model has been verified at a low-temperature condition (~5 K) and then applied to various oxygen environments over an extended temperature range with an overall error of less than ±10 %. The current O2 REMPI spectral model is an improvement over a previously reported version in both accuracy and the quantity of lines fit to provide rotational temperature measurements. This work details an optimized model that fits simulated spectra to full experimental spectral bands over various conditions with a wide temperature range, including both low temperature ( 1300 K).

Energy Efficiency Comparison between Compact Fluorescent Lamp and Common Light Bulb.

For acquainting the students of applied physics and students of teaching physics with the concept of energy efficiency, electrical and spectral characteristics of two widely used lamps – integrated fluorescence lamp and common light bulb have been investigated. Characterization of the lamps has been done by measuring the spectral irradiance and constructing the voltage-current characteristics. Breaking voltage, electric resistance, energy efficiency, energy consumption and intensity spectral distribution, were determined. Also, the quantity of mercury present in the fluorescence lamp was determined by analysis of the spectral characteristics. The energy efficiency advantage of the fluorescence lamp over the common light bulb was shown through comparison of the examined parameters of the two lamps.

Propagation characteristics of a non-uniformly Hermite–Gaussian correlated beam

We introduce a new kind of partially coherent beam, non-uniformly Hermite–Gaussian correlated beam, by employing a non-uniformly Hermite function to modulate the spectral degree of coherence. The evolution of such scalar beam on propagation in free space and turbulent atmosphere are investigated. It is demonstrated that the spectral intensity distributions exhibit extraordinary propagation characteristics, such as self-focusing and laterally shifted intensity maxima. The position of the maximum intensity and the intensity profile can be controlled by the order of the Hermite function. The results can be useful in free-space optical communications and beam shaping.

Overview spectra and axial distribution of spectral line intensities in a high-current vacuum arc with CuCr electrodes

Spectroscopic investigations of free-burning vacuum arcs in diffuse mode with CuCr electrodes are presented. The experimental conditions of the investigated arc correspond to the typical system for vacuum circuit breakers. Spectra of six species Cu I, Cu II, Cu III, Cr I, Cr II, and Cr III have been analyzed in the wavelength range 350–810 nm. The axial intensity distributions were found to be strongly dependent on the ionization stage of radiating species. Emission distributions of Cr II and Cu II can be distinguished as well as the distributions of Cr III and Cu III. Information on the axial distribution was used to identify the spectra and for identification of overlapping spectral lines. The overview spectra and some spectral windows recorded with high resolution are presented. Analysis of axial distributions of emitted light, which originates from different ionization states, is presented and discussed.

Strongly driven nonlinear quantum optics in microring resonators

We present a detailed analysis of strongly driven spontaneous four-wave mixing in a lossy integrated microring resonator side-coupled to a channel waveguide. A nonperturbative, analytic solution within the undepleted pump approximation is developed for a cw pump input of arbitrary intensity. In the strongly driven regime self- and cross-phase modulation, as well as multi-pair generation, lead to a rich variety of power-dependent effects; the results are markedly different than in the low power limit. The photon pair generation rate, single photon spectrum, and joint spectral intensity (JSI) distribution are calculated. Splitting of the generated single photon spectrum into a doublet structure associated with both pump detuning and cross-phase modulation is predicted, as well as substantial narrowing of the generated signal and idler bandwidths associated with the onset of optical parametric oscillation at intermediate powers. Both the correlated and uncorrelated contributions to the JSI are calculated, and for sufficient powers the uncorrelated part of the JSI is found to form a quadruplet structure. The pump detuning is found to play a crucial role in all of these phenomena, and a critical detuning is identified which divides the system behaviour into distinct regimes, as well as an optimal detuning strategy which preserves many of the low-power characteristics of the generated photons for arbitrary input power.

Probing interactions between Rydberg atoms with large electric dipole moments in amplitude-modulated electric fields

Dipole-dipole interactions between helium atoms in Rydberg-Stark states with principal quantum number $n=53$ and approximately linear Stark energy shifts, resulting from induced electric dipole moments of approximately 7900 D, have been investigated experimentally. The experiments were performed in pulsed supersonic metastable helium beams, with particle number densities of up to $\sim10^9$ cm$^{-3}$. In the presence of amplitude-modulated, radio-frequency electric fields, changes in the spectral intensity distributions associated with the transitions to these states that are attributed to dipole-dipole interactions within the ensembles of excited atoms have been observed. The experimental results are in excellent agreement with calculations of the Rydberg energy level structure carried out using Floquet methods, and excitations shared by up to 4 atoms. The use of these Rydberg-Stark states as sensors for non-resonant broadband radio-frequency electrical noise is also discussed.

Spectropolarimetric analyses of optical single mode SU8 waveguide layers

Abstract The paper presents the principle of the operation of a spectropolarimetric interferometer. In a planar waveguide orthogonal modes of the TE and TM types can be excited for the entire visible light. During the propagation the difference of the phases between the modes was determined, which is the function of the length of the path of propagation, the difference of the effective refractive index (NTM-NTE) and the wavelength. At the output of this system the spectral distribution of intensity was recorded, the shape of which depends on the value of the refractive index of the cover of the waveguides

Spectral intensity distribution of trapped fermions

To calculate static response properties of a many body system, local density approximation (LDA) can be safely applied. But applicability of LDA is limited for the case of dynamical response functions since dynamics of the system needs to be considered as well. To examine this in the context of cold atoms, we consider a system of non-interacting spin-$1/2$ fermions confined by a harmonic trapping potential. We have calculated a very important response function, the spectral intensity distribution function (SIDF), both exactly and using LDA at zero temperature and compared with each other for different dimensions, trap frequencies and momenta. The behavior of the SIDF at a particular momentum can be explained by noting the behavior of the density of states (DOS) of the free system (without trap) in that particular dimension. The agreement between exact and LDA SIDFs becomes better with increase in dimensions and number of particles.

Two-dimensional spectroscopic observation of a pulse-modulated induction thermal plasma torch for nanopowder synthesis

The two-dimensional distributions of spectral radiation intensities in the plasma torch were observed for the pulse modulated induction thermal plasmas (PMITP) with continuous or intermittent feedstock feeding for TiO2 nanopowder synthesis. For this observation, an imaging spectrophotometer with a high speed video camera were adopted. The evaporation of feedstock Ti powder, the formation of TiO and TiO transportation were investigated from the observation results of a Ti atomic spectral line and TiO molecule spectra as well as those of Ar and O atomic lines. An interpretation was suggested from the observation results for Ti feedstock evaporation and TiO formation in nanoparticle synthesis using a PMITP with intermittent feedstock feeding.

Validation study of a turbulence radiation interaction model: Weak, intermediate and strong TRI in jet flames

Abstract A TRI methodology developed previously for hydrogen jet flames is applied to carbon monoxide and methane jet flames. The paper demonstrates that the TRI methodology can accurately predict the spectral intensity distribution and heat flux distribution across a range of jet flames. A β probability density function (PDF) together with Reynolds averaging of the instantaneous properties along rays traversing the flames is used to prescribe the instantaneous incident intensity. Unlike most other studies in this area the model is used to predict the heat flux distribution as well as the spectral intensity. The underlying reason why hydrogen jet flames exhibit strong TRI compared to carbon monoxide and methane is also considered and shown to be a complex phenomena deserving of more research. The paper demonstrates that for the data available the heat flux distribution tends to be more sensitive to TRI than the spectral intensity distribution. Another interesting finding is that TRI can reduce as well as enhance the spectral intensity.

Processes of (Xe2D)*-excimer complex formation in ternary solid Kr-Xe-D2solutions

The article presents study results of VUV and UV cathodoluminescence spectra, of solid ternary Kr-Xe-D2 solutions, and Xe-D2, Kr-D2, Xe-Kr solid binary cryoalloys. The object of study is the dependence of the spectral band intensity distribution, on the concentration of impurities, and the dosage dependence of luminescence. All emission bands were identified. It is demonstrated that the formation of emitting states is caused by a transfer of energy through the system of its own electron excitation matrices. An emission from (Xe2D)* complexes is observed, if Xe is present in ternary solid solutions. It is shown that the process of forming (Xe2D)*-complexes has multiple steps, and includes the formation of an intermediate [XeD2]* non-stable state at the first stage, the nonradiative decay of which leads to the dissociation of the admixture molecular deuterium. It is suggested that the formation of [XeD2]* complexes occurs due to the high proton affinity of Xe, and its negative affinity to the electron in the D2 molecule, as a result of which, the intermediate complex acquires the features of a charge-transfer complex.