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We present our findings on the use of diode laser spectroscopy (DLS) for monitoring СО2, Н2О, СН4, C2H2, C2H4, NH3, and other gas impurities during low-temperature fractional distillation purification of gaseous hydrides. We demonstrate a lineup of instruments and techniques for continuously monitoring impurities during purification of hydrides: NH3, AsH3, РН3, and SiH4. The IR sources used are distributed feedback diode lasers (DLs) having a single mode output fiber pigtail and covering the near-IR spectral region, from 0.7 to 2.0 μm, where overtone and combination absorption bands of the impurities of interest are located. The systems offer high sensitivity and speed in impurity concentration measurements. Owing to their small size and low energy consumption, they can readily be integrated into a process equipment (components of fractionation columns) and enable prolonged continuous monitoring of the purity of hydrides. We describe gas concentration measurement techniques that use conventional high-resolution differential absorption spectroscopy and new, modulation correlation approaches for monitoring a weak molecular absorption by an impurity of interest against a strong selective absorption background of a matrix substance (hydride under study). We present results of technological experiments concerned with the low-temperature fractional distillation of hydrides and the degree of impurity removal from them as monitored by DLS.

Low-frequency (flicker) noises of the intensity and frequency of diode laser (DL) radiation have been studied. A model of DL flicker noise and a method for minimizing flicker noise at which the relative photocurrent noise can be registered at a level of 5 × 10–7 with an averaging time of 100 ms are proposed. The results obtained can be used in the development of DL-based gas-analytical equipment for measuring low gas concentrations.

A rationale for the concept and strategy of monitoring of the atmospheric chemical composition and water quality are provided for manned spacecraft to be used for long-term and interplanetary flights. The main risk factors are formulated for a change in atmospheric and water composition during interplanetary space flights. A promising version of the analytical system for operational control of air and water quality in manned spacecraft is described considering these risk factors. Several gas analysis methods are proposed to be used in this system to partially overlap the nomenclature of detected species with respect to particularly important (critical) species. The water quality in the system is monitored by two instruments: one for measuring the total carbon content and the other for analyzing the ionic composition of water.

In this paper, we present the most important principles of diode laser spectroscopy, which allow one to create fundamentally new measuring systems for diverse applications in biology and medicine. Using the diode laser spectroscopy method and its primary hardware implementation the emission of gas molecules from skin of the hand was registered and ammonia skin emission was found to be dominant. The properties of exhaled air from patients in different states were determined with another special measuring complex of diode laser spectroscopy. It was shown that when the functional state of the body changes, the gas composition of molecular substances that are present in the exhaled air is altered indirectly and their levels vary significantly depending on the health of the individual. Our findings suggest that it is possible to study the specific functional properties of the human body to facilitate assessment of the health of an individual to determine whether pathological processes occur in the body at various stages of their severity using diode laser spectroscopy. This paper presents clinical and experimental data on this issue.

A concept and strategy of the monitoring of chemical composition of the atmosphere in manned spacecrafts applicable during long-term and interplanetary flights are considered. The suggested concept and strategy are applicable for the life support system in spacecraft, which includes a system of gas composition support, a water supply system, a system of sanitary and hygienic support, a food supply system and a thermal control system. Major risk factors related with changes of the atmosphere composition during interplanetary space missions are evaluated. An advanced design of the analytical complex is described for the control of air quality in manned spacecraft's taking into account these risk factors. The simultaneous use of several methods of gas analysis is proposed together with partial overlapping of the set of substances to be detected with regard to the substances of particular (critical) importance. Application of such gas control system will provide a tool for the analyzing of a wide range of substances and will ensure the analysis of the atmosphere even in case of the failure of some of its parts.

The conceptual provisions and strategical aspects of the monitoring of the chemical composition of the atmosphere at manned spacecrafts and space stations which can be used in the execution of long-term and interplanetary space flights are proposed and substantiated. The major risk factors of the change in the composition of the atmosphere in the case of interplanetary space flights are formulated. Current advances in the field of monitoring are critically evaluated, which allows the choice of directions for new domestic designs to be substantiated. A promising version of an analytical complex for the operational control of the quality of the air in manned spacecrafts and space stations is described that takes into account the major risk factors. To provide the partial overlapping of the nomenclature of the detectable substances in terms of the most important (critical) compounds, it is proposed to simultaneously use several methods of gas analysis based on different physical principles. It is concluded that the implementation of such a monitoring system will make it possible to analyze a wide range of substances on a full scale and will provide an operational analysis of the quality of the air in manned spacecrafts and space stations, not only in usual operations but also in contingency (emergency) events.

Intracavity optics of e-beam-pumped high-energy KrF lasers should survive in a hostile environment of simultaneous irradiation by intensive UV laser light, scattered electrons, bremsstrahlung X-ray radiation, and permanent etching by a fluorine-containing working gas mixture. The present paper is focused on the research and development of high-optical-strength and fluorine-resistant AR coatings capable of protecting the fused silica windows and HR rare mirrors of these lasers against fluorine attack. The most promising coatings deposited by e-beam evaporation were N d F 3 -based compositions, which have low water content, good resistance to fluorine, and demonstrated the highest damage thresholds for AR coatings 29.8 J / c m 2 in a large irradiation spot. Outstanding “water-free” coatings of M g F 2 and A l 2 O 3 were deposited by C O 2 laser evaporation with preliminary laser treatment of substrates.

In this article, the results of investigation of processes occurring during the molecular-beam deposition of germanium layers on Si$_3$N$_4$ dielectric substrates within a wide range of the Ge film growth temperatures (30 to 600{\deg}C) are presented. The intensity of the IR absorption bands related to the vibrations of the N$-$H and Si$-$N bonds are established to decrease with the increase of the Ge deposition temperature. It appears that this phenomenon cannot be explained only as a thermally activated process. Simultaneously, the peak corresponding to the Ge$-$N vibration bonds emerges in the X-ray photoelectron spectra. We suppose that the deposition of germanium layers on Si3N4 dielectric substrates containing hydrogen atoms causes the diffusion of hydrogen atoms from the dielectric layer into the growing film. The experimental results may be interpreted in terms of a model, according to which the migration of hydrogen atoms from the Si$_3$N$_4$ layer into the growing germanium film is due to the difference in chemical potentials of hydrogen atoms in the dielectric layer and the germanium film. This process initiates the diffusion of germanium atoms in the opposite direction, into the Si$_3$N$_4$ layer, where they connect to free bonds of nitrogen atoms arising due to the escape of hydrogen atoms. The analogous processes occur during the deposition of silicon layers on Si$_3$N$_4$ substrates., Comment: 38 pages, 9 figures

Absorption spectra of the Q-branch of the ν1 + ν3 vibrational–rotational band of uranium hexafluoride (UF6) recorded in a range of 1290.0–1292.5 cm–1 using a laser spectrometer based on a quantum cascade laser have been studied. The spectra of samples with a natural isotopic composition (0.7% U235), an enriched sample (90% U235), and their gas mixtures (2, 5, and 20% U235) in a pressure range of 10–70 Torr at a temperature of T = 296 K have been analyzed. The experiments have revealed a highly reproducible fine structure of the recorded spectra. Periodic singularities in the fine-structure spectra have been interpreted as a manifestation of hot band transitions near the Q-branch. Anharmonicity constants X21, X31, and X32 and their combinations Xi1 + Xi3 (i = 4, 5, 6) have been determined. The characteristic features in the fine-structure spectra and the initial spectrum have been used to determine the isotopic composition of enriched UF6 samples.

The IR absorption spectra of the ICAO taggants, ethylene glycol dinitrate (EGDN), o-mononitrotoluene (2-NT), p-mononitrotoluene (4-NT) and 2,3-dimethyl-2,3-dinitrobutane (DMDNB) in the vapor phase, are studied at room temperature over a wide frequency range (500–4000 cm–1). The pre-assignment of the observed vibrational bands was performed. Modern quantum-chemical methods are applied to calculate the equilibrium geometries of these molecules and the frequencies of their fundamental vibrations. For the most intense bands of 2-NT and 4-NT, the absorption cross sections are estimated. Based on analysis of current laser technology, it has been concluded that their use in conjunction with the available spectroscopic data makes it possible to reliably perform local and remote detection and identification of ICAO taggants in an open atmosphere in real time.

The FTIR spectra of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and pentaerythritol tetranitrate (PETN) in the vapor phase over wide frequency (3500–500 cm−1) and temperature ranges (293–383 K) is experimentally studied and the assignment of the observed vibrational bands is performed. To clarify the nature of the physicochemical processes that occur during the heating and evaporation of RDX and PETN and to detect and identify their characteristic components, the mass spectra and sub-THz spectra of these explosives are studied. To obtain spectroscopic information, special experimental techniques for recording of IR, sub-THz, and mass spectra of vapors of explosives and for preparation of high-purity RDX and PETN samples (with a main substance content of >99.7%) are developed based on modern methods of synthesis and purification.

The transmittance spectra of epitaxial Pb1 − xEuxTe (0 ≤x ≤ 0.1) alloy layers are exploited to study the dispersion of their refractive index in the spectral range from 650 to 8000 cm−1 (below the absorption edge). The refractive index and the position of the absorption edge as functions of the composition parameter of the alloys are determined at two temperatures, 80 and 295 K. The refractive index is calculated in the context of the classic wave concepts of propagation of electromagnetic radiation. The experimentally determined dispersion dependences are described by the empiric Sellmeier expression of the second order. From analysis of the transmittance of the layers, it follows that the band gap of the epitaxial Pb1 − xEuxTe alloys increases with increasing temperature at x 0.5.

Using the TDLS method it has been found that ammonia (NH3) is the main impurity in arsine (AsH3) and phosphine (PH3), produced by hydrolysis of magnesium arsinide and phosphinide, respectively. NH3 behavior is abnormal in solutions of these hydrides: NH3 reveals the properties of a more volatile impurity in relation to arsine and phosphine, although its boiling temperature is higher than that of AsH3 and PH3. The observable anomaly is connected with the fact that in solutions of arsine and phosphine NH3 shows properties differing from the properties of pure ammonia. It was supposed that the influence of intermolecular interaction between ammonia molecules, when diluted by arsine or phosphine, decreases. During the purification of arsine or phosphine one must continuously monitor the NH3.concentration in the extraction of the light fraction in order to define the point at which to terminate the purification process.

As explosives are unstable, their decay products may be targeted for detection by means of tunable diode laser spectroscopy (TDLS). A model in which an explosive is placed inside an envelope with a hole in it has been studied. It has been shown that outside the envelope the concentration of the decay products may exceed that of the vapors of an explosive, by several orders.

The aim of this work was the development of an as-simple-as-possible instrument for trace moisture concentration measurements in high-purity ammonia. A near-infrared diode-laser-based instrument has been applied to measure the humidity in a process of on-line detection of water in ammonia during industrial purification. The results of water concentration measurements were compared with alternative techniques (primarily dew-point detection) and good agreement was achieved. The long-term sensitivity of such a diode-laser-based instrument was estimated to be 5 ppm. The calculation of the water concentration from measurements of the integrated volume of water contained in the heavy fraction, extracted during the purification process, yields an even lower detection limit of less than 0.1 ppm, depending on the initial ammonia purity.

Measurements of the content of various molecular impurities in the ambient air using helicopter- and aircraft-borne systems represent an extremely urgent challenge. In this respect, of special interest are the devices that that provide leakage monitoring in gas lines in order to prevent emergencies. In the paper results of the tunable diode laser-based instrument development and testing are presented.

Physics and technology of Krypton Fluoride (KrF) laser have been studied experimentally and theoretically to improve its efficiency and to increase a lifetime, and thus to verify the challenge of KrF laser for Inertial Fusion Energy (IFE). Experiments were performed with e-beam-pumped multistage 100-J output energy GARPUN KrF laser facility and 200-A/cm 2 current density EL-1 electron gun, both operating at P.N. Lebedev Physical Institute. They formed the database for verification of numerical codes capable to predict IFE-scale KrF drivers. Monte Carlo code was developed to calculate e-beam energy deposition inside GARPUN laser chamber while a quasistationary numerical KrF laser code based on generalized "forward-back" multi-direction approximation for radiation transfer equation was used to describe amplification of nanosecond pulses and amplified spontaneous emission (ASE). Long-lived absorption in UV optical materials induced by fast electrons and bremsstrahlung X-ray radiation was measured at EL-1 electron gun with total fluence of ionizing radiation up to 20.6 kJ/cm 2 . Using these data together with measurements and scaling of bremsstrahlung X-ray yield, we can predict that the most stable windows of IFE-scale KrF laser driver would be able to withstand no less than 2 × 10 6 shots. Fluorine-resistant coatings onto fused silica windows of KrF laser were developed and demonstrated damage thresholds as high as 29 J/cm 2 in test experiments with large 13 x 13-mm uniformly irradiated spot.

The results of experimental and theoretical investigations of the photodissociation XeF laser operating in the visible and UV regions and pumped by the radiation of an open discharge initiated by an electric explosion of thin metal wires are reported. A detailed description of the laser design and experimental techniques is given. The analysis of the energy balance in the XeF laser on the basis of measurements of energetic parameters of laser radiation and the pump source are performed. The results of optical investigations of the active medium aimed at the study of the interaction of high-power fluxes of pump radiation with the absorbing active medium are presented. This interaction forms free-running bleaching and inversion waves in the active medium. Spectral, spatial, time, and energy characteristics of laser radiation on theB-X(λ=353 nm) andC-A(λ=480 nm) transitions of XeF are investigated. The instantaneous laser efficiency with respect to the electrical power feeding the pump source is shown to be about 1%. The specific energy of laser radiation on theC-A transition in the blue-green region was 8.5 J/liter for a total laser energy of 14.5 J. The specific energy of radiation on theB-X transition in the UV region was 16.5 J/liter for a total energy of 28 J.

The present work reports on detection of explosives substances (NG, TNT, RDX) in subTHz and midIR, based on registration of certain marker-molecules evaporated from surfaces of samples. Experimental results of both methods are in good agreement and have demonstrated a presence of nitric oxides, ammonia, acetone, etc in explosives vapors.

Protective single-layer, AR double-layer, and HR multi-layer fluorine-resistant coatings with damage thresholds as high as 20 J/cm 2 were deposited for the intracavity optics of high-energy KrF lasers by using different deposition techniques. They were tested by the atomic-force microscopy and IR Fourier spectrometry in regard of microstructure, porosity, water content, and in prolonged etching by fluorine. The most promising were NdF 3 -based AR and HR coatings produced by e-beam evaporation, while outstandingly low water content was demonstrated for MgF 2 and Al 2 O 3 layers deposited by laser evaporation with a preliminary laser treatment of substrates.

The objective of this work was investigation of possibility of tunable diode laser spectroscopy (TDLS) technique application for gaseous uranium hexafluoride (UF6) isotope measurement. Spectra of uranium hexafluoride gas mixture were investigated using two different Fourier Transform Spectrometers Vector 22 and Bruker 66v. Observed spectral features were identified and model spectra of different gas mixture components were developed. Optimal spectral range for measurements was determined near maximum of UF6 combination band nu1+nu3. Laboratory prototype of multi-channel instrument under consideration based on tunable diode lasers was built and algorithms were developed to measure gaseous UF6 isotopic ratios. Diode laser used operated at the wavelengths near lambda=7.68 microm. It was placed in a liquid nitrogen cooled cryostat. Three instrument channels were used for laser frequency calibration and spectra recording. Instrument was tested in measurements of real UF6 gas mixtures. Measurement accuracy was analyzed and error sources were identified. The root-mean-square random error in the 235U isotopic content is characterized by a spread of about 0.27% for quick measurements (at times less than 1 min) and 1% for periods of more than an hour. It was estimated that the measurement accuracy could be improved by at least an order of magnitude by minimizing the error sources.

The operating principle of a photodissociation XeF laser (λ≅350 nm) is discussed. A laser operating on the gas mixture XeF2:N2(SF6):Ar pumped by radiation from an open high-current discharge is described. The maximum lasing duration is 5 μsec, the maximum output energy is 0.15 J. The vibrational structure of the XeF-molecule transition B2Σ1/2 + − X2Σ1/2 +, observed in absorption, luminescence, and stimulated emission, is investlgated. The vibrational quantum and the anharmonicity in the upper and lower states are measured: ωe ' = 308.7 cm-1, ωe 'xe ' = 1.44 cm-1, ωe '' = 225.7 cm-1, ωe ''xe '' = 11.0 cm-1. The difference between the equilibrium internuclear distances of the XeF molecule is determined for the excited (B) and ground (X) states, namely re ' - re '' = 0.33 +- 0.01 A.

An investigation was made of the photoluminescence spectrum and quantum efficiency of gaseous Xe at pressures of 0.5–20 atm. It was found that the gain of an optically pumped Xe2 laser could be ~10–2cm–1.

An experimental investigation was made of the optical strength of semitransparent metal-dielectric (Al+MgF2) resonator mirrors of a xenon laser. The highest optical strength was exhibited by coatings deposited on a substrate with a high thermal conductivity (Al2O3).