Monochromatic Radiation Source Research Articles

Terahertz Resonant Emission by Optically Excited Infrared-Active Shear Phonons in KY(MoO4)2.

The generation of monochromatic electromagnetic radiation in the terahertz (THz) frequency range has remained a challenging task for many decades. Here, the emission of monochromatic sub-THz radiation by optical phonons in the dielectric material KY(MoO4)2 is demonstrated. The layered crystal structure of KY(MoO4)2 causes infrared-active shear lattice vibrations to have energies below 3.7meV, corresponding to frequencies lower than 900GHz where solid-state-based monochromatic radiation sources are rare. Directly excited by a 5ps long broadband THz pulse, infrared-active optical vibrations in KY(MoO4)2 re-emit narrowband sub-THz radiation as a time-varying dipole for tens of picoseconds, which is exceptionally long for oscillators with frequencies below 1THz. Such a long coherent emission allows for the detection of more than 50 periods of radiation with frequencies of 568 and 860GHz. The remarkably long decay time together with the chemical stability of the employed material suggests a variety of possible applications in THztechnology.

Iterative approach for photonic crystal devices design

Background. An approach to the design of photonic crystal (PhC) devices is proposed, which differs from the known general-purpose optimization methods (for example, a genetic algorithm or gradient procedures) by using information about diffraction patterns at different frequencies when optimizing an element designed to operate at the selected wavelength. The following is an approach to the design of photonic crystal elements. The proposed approach differs from known general-purpose optimization methods (e.g., genetic algorithm or gradient procedures) by using diffraction pattern information at different frequencies while optimizing an element designed to operate at the selected wavelength. The design of functional PhC structures with expected characteristics (for example, waveguides) for a certain wavelength (albeit given by a monochromatic radiation source) is described. Aim. Development based on the FDTD method and confirmation of the functionality of the iterative procedure for calculating the characteristics of metal-dielectric PhC lattices. Methods. The study is based on an iterative approach to the design of PhC elements based on the use of the FDTD method. Results. Model examples were used for demonstration of practical convergence and applicability of the developed iterative procedure. The efficiency of the PhC waveguide, understood as the ratio of the output energy to the input energy, was increasing at each iteration up to 97.2%. Conclusion. The method of synthesis of metal-dielectric PhC structures with preset properties based on application of developed iterative procedure is proposed and argued. The results of the analysis of the 2D PhC waveguide based on a set of round copper rods show the applicability of the proposed method.

Spectral Characteristics of Polarization Radiation in the Water Window Range

The high-intensity and monochromatic radiation sources in the water window spectral range are desirable for many applications. One of the potential candidates of soft X-ray sources is polarization radiation produced by a charged particle passing through a thin foil. In the soft X-ray range near the absorption edges of a target material, the real part of dielectric permittivity can exceed unity, and the Tamm–Frank criterion is fulfilled. Thus, two types of radiation are produced: transition and Cherenkov radiation. In this report, we theoretically investigated the spectral characteristics of radiation produced in both cases when the Tamm–Frank criterion is met or not met. We showed the dependences of the spectrum as a function of thickness and the incidence angle. To describe the properties of polarization radiation and the complex dielectric permittivity, the polarization current approach and Henke’s model were used, respectively.

Excitation of Terahertz Plasmonic Resonance on a Subwavelength Metallic Grating in an Attenuated Total Reflection Scheme Using a Monochromatic Radiation Source

Excitation of Terahertz Plasmonic Resonance on a Subwavelength Metallic Grating in an Attenuated Total Reflection Scheme Using a Monochromatic Radiation Source

IDENTIFICATION AND AUTHENTICATION OF COW’S MILK POWDER USING A SMARTPHONE AND CHEMOMETRIC ANALYSIS

The possibility of identi cation and authentication of cow’s milk powder by the method of chemical colorimetry of the samples’ own uorescence using a smartphone camera and chemometric analysis is shown. A fundamental test device for direct colorimetric analysis of powdered milk is proposed, excluding the stage of sample preparation. Fluorescence excitation was carried out with a portable source of monochromatic UV radiation (λ = 365 nm). Colorimetric parameters of powdered milk uorescence in RGB space were recorded using a smartphone camera. We used chemometric processing of the calculated analytical signal, which made it possible to reduce the analysis time and visualize the study data. The evaluation of the data array of uorescence colorimetric parameters (RGB) was carried out by principal component analysis (PCA) and hierarchical clustering analysis (HCA) using the XLSTAT software.

Interference of areas of subcycle light pulses

Progress in reducing the duration of light pulses (down to one cycle of field oscillations or less), achieved in the last decades, has made it possible to experimentally observe and study a number of atomic-scale phenomena that occur at ultrafast times. Their study and observation are unavailable with conventional sources of monochromatic laser radiation. When using few- or subcycle pulses, a number of well-known phenomena in optics, which are well studied when using long monochromatic radiation sources, either lose their meaning, or their underlying physical mechanisms require revision. For example, the direct interference of subcycle pulses with their direct overlap is not possible due to their short duration. This note addresses the interference phenomenon, when a pair of subcycle pulses act on a medium, while do not simultaneously overlap inside it. In this case, it is not the pulses themselves that interfere in the medium, but the probability amplitudes of the bound states of the medium. Therefore the result of their impact on the medium can be interpreted as the interference of the areas of pulses—electric pulse areas (integral of the electric field strength over time) and envelope areas (integral of the slowly varying envelope of the electric field strength over time).

Spectrophotometric Techniques: A Versatile Tool for Bioprocess Monitoring

Online analysis of bioprocesses by analytical spectroscopic methods is used to produce fast sample analysis. Bio-transformations are directly controlled by continuous process It improves management of Quality. Various methods for online analysis have been reported. This review article majorly covers applications for infrared [NIR and MIR]; Fluorescence; Ultraviolet [UV] Spectroscopy and Raman Spectroscopy for online monitoring of bioprocesses. The use of Uv- Vis spectroscopy in bioprocess monitoring to measure different chemicals compound present in sample. The measurement of proteins and other large molecule, where light is absorbed by functional group of molecules, resulting in non-specific uv-vis spectra. Raman spectroscopy is supportive to MIR, yielding different intensities and selectivity. Raman measures inelastic scattering from a monochromatic radiation source. Fluorescence spectroscopy monitoring and automation of fluorescence can be improved by using in combination with chemometric model for cultivation of e-coli. The application of spectroscopic methods for the analysis of bioprocess result in complex spectra. The methods under discussion produce datasets which overlapping spectra for all of these components which requires multivariate data analysis method, such as Partial least square (PLS), regression or principal component regression for data analysis also the use of calibration dataset and chemometric algorithms which is beyond the scope of review.

Monochromatic Radiation Source Based on a Supercontinuum Laser for Measurement of Spectral Sensitivity of Radiation Detectors in the Range 0.9–1.6 μm with the Use of an Absolute Cryogenic Radiometer

An improved monochromatic radiation source with spectral width 4 nm based on a supercontinuum laser and double monochromator is introduced into a unit based on an absolute cryogenic radiometer in order to increase the precision of measurement of spectral sensitivity in the range 0.9–1.6 μm. A feedback system that supports stabilization of the power of monochromatic radiation with standard deviation 0.025% is developed. The power of optical radiation in the plane of the detector and/or power of the absolute cryogenic radiometer varies from 0.1 to 1.5 mW. The spectral distribution of the power of the newly developed source in different operating regimes of the supercontinuum laser is presented.

Terahertz Scanning Reflectometer for Structure Visualization of Polymer Constructions in Additive Manufacturing

The results of the development and practical application of a quasi-optical system for reflectometry of objects in the terahertz frequency range for analyzing the structure in additive manufacturing of objects are presented. A backward-wave oscillator is used for continuous generation of electromagnetic radiation; an acousto-optic converter (Golay cell) is applied as a detector. The reflectometer is controlled by personal computer through the L-card E 154 input-output module and the standard digital-to-analog converter of the STD-21 spectrometer. The system is tested at the frequency of 874 GHz on the 3D-printed composite structure sample. Our paper is terahertz reflectometer with a source of continuous monochromatic electromagnetic radiation based on a backward wave oscillator is presented. The purpose of this work in creating a scanning THz reflectometer is considered to have been achieved. At the same time, the following tasks are solved: a quasi-optical scheme of the reflectometer is selected and assembled; the hardware part of the system (all mechanisms and components) is implemented; a program for controlling the radiation intensity registration system is adapted for this task; the test sample is manufactured using 3D printing technology, the THz reflectometer is tested. The obtained practical results of registration of the two-dimensional distribution of the reflection coefficient show that the use of THz radiation is promising for visualizing the structure of structures obtained by additive technology. Further development of the project is planned by changing the construction of the positioning mechanism, which will provide micrometric calibration of the sample holder relative to the diaphragm. The use of the quasi-optical scheme of the two-beam interferometer for recording the phase distribution and amplitude of reflected THz radiation will allow obtaining information about the spatial location of defects (inhomogeneities) of products obtained by additive technology.

Biological Risks of Using Non-Thermal Non-Ionizing Electromagnetic Fields

Electromagnetic pollution of the environment has become a significant environmental factor. The intensity of technogenic electromagnetic fields far exceeds the background indicators to which organisms have adapted in the course of evolution, in particular by their biorhythms. Much data on the biological effects of low-intensity (non-thermal) extremely high-frequency electromagnetic fields (EHF-EMF) at different levels of the organization has been accumulated. There are many possible explanations for these impacts, but the mechanism of action is not established. The purpose of this work is to analyze the negative effects of the use of non-thermal coherent electromagnetic radiation of extremely high frequencies. In particular, the use of microwave therapy is considered. A review of reports on the harmful effects of non-ionizing electromagnetic and magnetic fields among the population and professional groups has been made; the presence of the problem of hypersensitivity to such fields was shown. Information on the development of the direction of study of the resonant biological influence of EHF-EMF by Ukrainian specialists was provided. Particular attention is paid to the use of non-thermal microwaves for physiotherapy procedures, pain relief, correction of psycho-emotional disorders, ulcer healing, in particular stomach and duodenum, etc. It is noted that the so-called therapeutic frequencies of EHF-EMF, even if controlled, can cause negative effects, although they are not perceived as damaging. Changes in objective vital signs in the case of targeted exposure by low-intensity millimeter-wave radiation, namely, hemodynamics, temperature increase in the exposure zone, muscle activity, and the speed of the passage of a nerve impulse, an encephalogram were established. Precautionary recommendations based on the scientific and practical experience of using microwave acupuncture methods in the conditions of medical institutions are formulated. The synergistic effect of various influences, in particular electromagnetic fields, may not be a direct trigger of the disease, but a factor of not compensated stress. Therefore, clinical studies conducted many years ago cannot simply be dismissed on the grounds that the millimeter radiation penetrates only the outer layer of the skin. Skin cells can also secrete mediators that cause changes in ionic calcium channels and the level of calcium in the cells. The interest in these works is justified by the fact that currently the sources of monochromatic millimeter radiation will be spread with new communication systems. The risks of their biological action should be taken into account when emitters are installed.

PinkIndexer - a universal indexer for pink-beam X-ray and electron diffraction snapshots.

A crystallographic indexing algorithm, pinkIndexer, is presented for the analysis of snapshot diffraction patterns. It can be used in a variety of contexts including measurements made with a monochromatic radiation source, a polychromatic source or with radiation of very short wavelength. As such, the algorithm is particularly suited to automated data processing for two emerging measurement techniques for macromolecular structure determination: serial pink-beam X-ray crystallography and serial electron crystallography, which until now lacked reliable programs for analyzing many individual diffraction patterns from crystals of uncorrelated orientation. The algorithm requires approximate knowledge of the unit-cell parameters of the crystal, but not the wavelengths associated with each Bragg spot. The use of pinkIndexer is demonstrated by obtaining 1005 lattices from a published pink-beam serial crystallography data set that had previously yielded 140 indexed lattices. Additionally, in tests on experimental serial crystallography diffraction data recorded with quasi-monochromatic X-rays and with electrons the algorithm indexed more patterns than other programs tested.

Suppressed Auger scattering and tunable light emission of Landau-quantized massless Kane electrons

The Landau level laser has been proposed a long time ago as a unique source of monochromatic radiation, widely tunable in the THz and infrared spectral ranges using an externally applied magnetic field. In spite of decades of efforts, this appealing concept never resulted in the design of a reliable device. This is due to efficient Auger scattering of Landau-quantized electrons, which is an intrinsic non-radiative recombination channel that eventually gains over cyclotron emission in all materials studied so far: in conventional semiconductors with parabolic bands, but also in graphene with massless electrons. The Auger processes are favored in these systems by Landau levels (or their subsets) equally spaced in energy. Here we show that this scheme does not apply to massless Kane electrons in gapless HgCdTe alloy, in which undesirable Auger scattering is strongly suppressed and the sizeable cyclotron emission observed, for the first time in the case of massless particles. The gapless HgCdTe thus appears as a material of choice for future technology of Landau level lasers.

A combined experimental and numerical approach for radiation heat transfer in semi-crystalline thermoplastics

This paper proposes a novel experimental-numerical approach for radiation heat transfer in semi-crystalline thermoplastics. The proposed experimental and numerical approaches were analyzed here for the case of IR heating of linear polyethylene (PE). The challenges for radiation transport in semi-crystalline polymers may be categorized into the two main aspects: optical heterogeneity in polymer medium due to semi-crystalline nature and, semi-transparency in certain type of such polymers, like PE. In this study, we address the temperature dependence in the thermo-optical properties of semi-crystalline thermoplastics concerning its effect as a thermal radiation parameter for radiation heat transfer modeling of such type of polymers. The temperature dependence in the optical properties of PE, namely transmittance and reflectance characteristics, were experimentally analyzed under heating condition and, the temperature-dependent thermo-optical properties of PE was determined. The experimental analyses showed that the change in the thermo-optical properties under heating is related to change in the optical scattering behavior in PE medium since it is strongly affected by its crystalline structure. The radiation heat transfer model was built based on optically homogeneous medium assumption at which the change in the amount of radiative energy absorbed by the PE medium under heating was introduced without modeling how the light scatters inside of the medium. Thus, the effect of optical scattering on the absorption characteristics of PE under varying temperature was taken into account without modeling the spatial distribution of the scattered light intensity at microscopic level, which offers computationally cost-effective numerical solutions. The accuracy of the numerical model was analyzed performing IR heating experiments where IR thermography and thermocouples were employed for the surface temperature measurements. Due to the semi-transparent nature of PE, an experimental method was developed for IR thermography of PE and its accuracy was analyzed. The experimental-numerical comparisons showed that the temperature field on PE can be closely predicted using its temperature-dependent thermo-optical properties. Thanks to the adopted comparative case study, it was demonstrated how the temperature field predictions may deviate from the experimental thermal measurements due to the ignorance of this temperature dependence. Considering any type of monochromatic or polychromatic radiation source, the combined experimental-numerical approach proposed here may be adopted for temperature field predictions and non-invasive surface temperature measurements on the radiatively heated semi-crystalline thermoplastics.-

Optically self-photopumped x-ray laser at 13.4 nm in Ni-like tin (Sn22+)

A model of the source of monochromatic radiation with λ ~ 13.4 nm with a high conversion factor, intended for industrial nanolithography, is presented. The source is based on an x-ray laser (XRL) on the transition 4f5/2 [J = 1] − 4d3/2[J = 1] of Ni-like tin ions (Sn22+) in plasma formed during the interaction of a nanostructured tin target with an intense ultrashort pump laser (Ipump ~ 8·1017 W cm−2). The inversion mechanism of the optically self-pumped laser is caused by photon reabsorption in optically dense plasma. Calculations of gains and quantum efficiencies of the XRL in Sn22+ with λ ~ 13.4 nm under optimal plasma conditions are discussed.

Smith-Purcell radiation from periodic beams.

Smith-Purcell effect is well known as a source of monochromatic electromagnetic radiation. In this paper we present the generalized theory of Smith-Purcell radiation from periodic beams. The form-factors describing both coherent and incoherent regimes of radiation are calculated. The radiation characteristics are investigated in two practically important frequency ranges, THz and X-ray, for two modulation profiles, most frequently used in practice - a train of microbunches and a Gaussian-shaped one, characterized by sinusoidal modulation with an arbitrary modulation depth. On the base of the theory developed we show that a modulated electron beam consisting of a set of bunches makes it possible to improve significantly the spectral line monochromaticity of the light emitted, reaching values better than 1% for short gratings. We demonstrate as well that Smith-Purcell radiation can be used for non-destructive diagnostics of the depth of modulation for partially modulated beams. These findings not only open up a new way to manipulate the light emission using Smith-Purcell effect but also promise a profound impact for other radiation sources based on charged particle beams, such as undulator radiation in FELs, next-generation X-ray radiation source based on inverse Compton scattering, in a wide range from THz to X-rays.

X-ray laser near 13.5 and 11.3 nm in Xe26+ driven by an intense pump laser interacting with xenon cluster jet as a promising radiation source for nanolithography

The model of highly efficient (yield ~0.1–1% of pumping energy) monochromatic radiation sources near λ = 13.5 and 11.3 nm, intended for commercial nanolithography is presented. The sources are based on x-ray lasers on four transitions: 3p53d104l–3p53d104l′ (λ near 13.5 nm) and self photo-pumped 3d 94f (J = 1)–3d 94d (J = 1) (λ ~ 11.3 nm) transition of Ni-like xenon (Xe26+). New inversion mechanisms are discussed. A sufficiently intensive pumping pulse interacting with xenon cluster jet forms plasma. Optimal plasma parameters and quantum yields are predicted for each x-ray laser line. At pump intensities ⩾1018 W cm−2, immediately after the interaction, plasma is formed in the state with dominating Xe26+ ions. This condition is absolutely necessary for the short-lived lasing at 11.3 nm and for the wavelengths of laser transition measurements.

Recovery and analysis of Raman spectra obtained using a static Fourier transform spectrometer

The recovery of Raman spectra in the 800-1050-nm spectral range from a prototype static Fourier-transform spectrometer is described. Distortion effects introduced by the optical system of the static Fourier-transform spectrometer are studied. A method of correcting optical distortion is suggested. The proposed algorithm is tested using a monochromatic radiation source. A two-dimensional map of period distribution in the distorted interference pattern is plotted. A mapping that enables optical distortions of the two-dimensional interferogram to be corrected is proposed. The correction results are demonstrated by plotting interference fringe profiles. A comparison of various well-known phase correction methods in order to identify an optimal algorithm is presented. A matching criterion for the obtained spectra is proposed. Raman spectrum of a stilbene crystal obtained by a diffraction spectrometer with a resolution of δν = 14 cm-1 is used as a reference.

Experimental K X-ray intensity ratios of some heavy elements

The K X-ray intensity ratios of some elements (Z&$2gt;70) were measured by using an Energy Dispersive X-Ray Fluorescence Spectrometer, which has an intense radioisotope source and an HPGe detector. The experimental results had uncertainties about 4% and were in good agreement with theoretical results of Scofield. In order to obtain more reliable results, the experiments should be carried out with synchrotron radiation having a more intense and monochromatic radiation source and detectors with better resolutions.

Molecular gas spectroscopy using radioacoustic detection and high-power coherent subterahertz radiation sources

We study the “power” approach to improve the sensitivity of the radioacoustic detection method by increasing the radiation power. A gyrotron is the source of high-power continuous monochromatic radiation in the spectrometer. As a result of analysis of experimental profiles of known lines of the rotational SO2 spectrum, it was demonstrated for the first time that an increase of radiation power by about three orders of magnitude leads to a proportional increase of the RAD spectrometer sensitivity. This permitted us, in particular, to observe the weak transitions predicted earlier in the SO2 molecule.

National Primary Standard for the Units of Absolute and Relative Spectral Sensitivity at Wavelengths from 0.25 TO 14.00 μm Get 213–2014

This is a discussion of the characteristics of a cryogenic radiometer and monochromatic radiation source that form part of the National primary standard GET 213–2014 for the units of absolute and relative spectral sensitivity at wavelengths from 0.25 to 14.00 μm and are intended for calibration of photodetectors with respect to spectral sensitivity.