Reducing the Energy Consumption of a Laser Photo-Acoustic SF<Subscript>6</Subscript> Gas Analyzer

Experimental studies of the operating modes of a laser photo-acoustic SF₆ gas analyzer that were aimed at reducing its energy consumption were carried out. It was shown in the experiments that an average power of CO₂ laser radiation of at least 100 mW is required for the assured detection of low SF₆ concentrations (less than 100 ppb). To reduce the energy consumption of the gas analyzer, it is proposed to decrease the repetition frequency of CO₂ laser pulses by several times and operate on subharmonics of the resonance frequency of the photo-acoustic detector. The experimental results made it possible to reduce the energy consumption of the gas analyzer to ~15 V A and use a Li-ion battery from a laptop to power it. The duration of the continuous operation of the gas analyzer on one battery charge was at least 6 h.     

A Laser Gas Analyzer

A high-sensitivity gas analyzer was developed to measure the concentration of individual gases in multicomponent gas mixtures. The gas analyzer consists of the following main elements: a waveguide CO₂ laser, a resonance optoacoustical cell, and a computer. The database of the computer contains information about absorption lines of 37 gases. The thresholds of the detection of individual gases by the gas analyzer are given. The ammonia detection threshold and error are 0.015 ppb and 15%, respectively.     

Single-Frequency TEA CO<Subscript>2</Subscript> Laser for Experiments on Non-Resonant Radiation Interaction with Matter

The design philosophy and output radiation parameters of single frequency TEA CO₂ laser with bleaching intracavity longitudinal modes selector (cell filled with SF₆) are described. At cavity tuning to 10P(16) line and choosing optimum SF₆ pressure in the cell the stable single frequency lasing is realized with scatter of radiation peak power in a series of “shots” less than ±7% of average value. The radiation energy density and intensity gradually tuned in the ranges 0.36–12.5 J/cm² and 2.9–100 MW/cm² correspondingly were realized in the focal plane of a lens with f = 127 mm.     

LASER PHOTOACOUSTIC TRACE GAS DETECTION,AN EXTREMELY SENSITIVE TECHNIQUE APPLIED IN BIOLOGICAL RESEARCH

Abstract

The use of infrared laser based photo-acoustic trace gas detection equipment in biological research is discussed on the basis of two examples. A CO₂ laser based photo-acoustic trace gas detection system is employed to follow the time-dependent pattern of the nitrogen fixation process by the cyanobacteria Nodularia Spumigena on a one-minute time scale. Due to the high sensitivity of the detection system for ethylene (detection limit 6 part per trillion; 6:10¹²), the fixation process can be followed on-line in a flow-through system. Following a 50 h dark incubation period, the bacteria show nitrogen fixation only after a certain illumination period, indicating lack of carbohydrates needed to start the nitrogen fixation.

Another, CO laser based, system allowed to monitor acetaldehyde emission (detection limit 0.1 part per billion) of Docks Rumex palustris during the change from anoxic environment to O₂ levels of air. An almost immediate emission is found, indicating that acetaldehyde plays an important role for post-anoxic injury in Rumex palustris.     

SF6气体检测技术的研究进展及发展趋势

针对高压设备SF_6气体泄漏检测问题,介绍了SF_6气体泄漏产生的危害。根据SF_6气体检漏技术的研究进展,可把SF_6气体泄漏检测技术分为非光学检测和光学检测两大类。对气体浓度监测技术、真空负离子捕获技术、紫外电离技术和负电晕放电技术等非光学检测技术进行简要的概述,同时对激光成像技术、红外吸收光谱技术和光声光谱技术等光学检测技术进行了重点阐述,并对比分析了各种技术的优缺点,提出了SF_6气体检漏仪的未来发展趋势。     

Characteristics of a pulse–periodic CO<Subscript>2</Subscript> laser for applications in the field of laser-produced plasma

The design of a pulse–periodic СО₂ laser oscillator that operates at a high level of the specific energy deposition into a self-sustained discharge is described. The laser is intended for generating pulses with a high-density radiation flux in a laser-plasma generator of multiply charged ions at the Institute of Theoretical and Experimental Physics (ITEP). The results of investigations of the spatiotemporal and energy characteristics of laser output radiation in a wide range of the discharge excitation level and the mixture composition are presented. The optimal conditions are determined under which the oscillator provides an output energy of >10 J in a pulse with a duration of ~28 ns and a record specific peak radiation power of 190 MW per liter of the active volume of a CO₂: N₂: He mixture. The high quality of the spatial characteristics was confirmed in measurements of the radial energy-density distribution in the far-field zone, whose characteristic size is close to the diffraction limit.     

A facility for studying the spatial and temporal characteristics of a plume produced by interaction of high-power CO<Subscript>2</Subscript> laser pulses with a solid-state target in various gas environments

An experimental facility for studying the kinetics of molecular association formation from atoms produced by evaporation of the target material by powerful CO₂ laser pulses is described. First experimental results are presented for the spectral and spatial-temporal characteristics of the spread of Al atoms produced in interactions of laser radiation with aluminum oxide Al₂O₃, followed by AlO formation in various low-pressure (0.1–0.3 Torr) atmospheres. Images of structurally similar forms condensed on a glass surface have been observed with an atomic-force microscope.     

Simultaneous measurement on gas concentration and particle mass concentration by tunable diode laser

The method of simultaneous measurement on gas concentration and particle mass concentration by tunable diode laser absorption spectroscopy is developed. The method is validated using a 1.58 μm diode laser with wavelength modulation spectroscopy. The experimental environment of particulated gas flow is imitated by adding uniform-sized quart sands into CO₂ gas. Calibrated second harmonic signals are proved to be independent of particle effects but only depend on gas concentration, and particle mass concentration can be calculated from the attenuation of laser power. This technique would be helpful to improve the quality and applicability of tunable diode laser absorption spectroscopy in emission monitoring.     

Registration of picosecond CO<Subscript>2</Subscript> laser pulses by means of two-stage parametric transformation in nonlinear crystals

A technique for registering the temporal structure of picosecond pulses of CO₂ laser radiation with an energy of 1.5–4.5 μJ at a wavelength of 10.27 μm using two-stage parametric transformation of IR radiation frequency into visible light under pumping of nonlinear crystals by Nd:YAG-laser radiation in a Q-switched mode is described. A GaSe nonlinear crystal was used at the first stage of transformation (10.27 μm + 1.064 μm → 0.964 μm). Radiation was further transformed (1.064 μm + 0.960 μm → 0.506 μm) by using the same pumping in an α-HIO₃ nonlinear crystal. For the first time, no additional optical elements were present between the stages of the frequency transformer in the proposed optical scheme. The transformed radiation was registered with a Hamamatsu Temporal Disperser C1587 streak camera in a region of the photocathode maximum spectral sensitivity of ～0.5 μm with a temporal resolution of up to 2 ps. The minimum recorded pulse duration of the CO₂ laser was ～45 ps.     

Development of fast-response portable NDIR analyzer using semiconductor devices

In this paper, a novel fast response NDIR analyzer (FRNDIR), which uses an electrically pulsed semiconductor emitter and dual type PbSe detector for the PPM-level detection of carbon dioxide (CO₂) at a wavelength of 4.28 μm, is described. Modulation of conventional NDIR energy typically occurs at 1 to 20 Hz. To achieve real time highspeed measurement, the new analyzer employs a semiconductor light emitter that can be modulated by electrical chopping. Updated measurements are obtained every one millisecond. The detector has two independent lead selenide (PbSe) with IR band pass filters. Both the emitter accuracy and the detector sensitivity are increased by thermoelectric cooling of up to —20 degrees C in all semiconductor devices. Here we report the use of semiconductor devices to achieve improved performance such that these devices have potential application to CO₂ gas measurement and, in particular, the measurement of fast response CO₂ concentration at millisecond level.     

Continuously wavelength tuned optical parametric oscillator based on fan-out periodically poled lithium niobate

A PC-controlled optical parametric oscillator (OPO) based on fan-out periodically poled lithium niobate (MgO : PPLN) structures was developed. Continuous wavelength tuning (2.40–3.85 μm) was realized via linear displacements of fan-out MgO : PPLN structures using a PC-controlled precision motorized translation stage. The total wavelength scanning time in the range of 2.40–3.85 μm was ≤1 min. The OPO was developed as a source of tunable radiation for use in a laser photo-acoustic gas analyzer. Studies of the methane absorption spectrum showed a good coincidence of the experimental and theoretical data.     

Analytical Standards

ABSTRACT

A simple system for recovering the helium (He) gas from the gas mixtures used in the CO₂ laser is discussed. Separation of the gases CO₂, N₂ and H₂ from He gas is accomplished by various chemical and physical processes. An example, including the dimension of the system and the quantity of the chemicals needed, is given for a Molectron Corporation model T250 CO₂ gas laser, based on an hour of operation. The cost and the efficiency of the system as well as the purity of the recovered He gas are analyzed.     

Determining the coefficient of transverse turbulent diffusion in a flow of the active medium of a CO<Subscript>2</Subscript> laser with fast axial gas circulation

A method for determining the coefficient of transverse turbulent diffusion in a flow of the active medium of a CO₂ laser with fast axial gas circulation is described. The method is based on the phase conjugation during degenerate intracavity four-wave mixing.__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 114–119.Original Russian Text Copyright © 2005 by Buyarov, Galushkin, Dubrov, Zavalov.     

A Raman Spectroscopic Study of MoS<Subscript>2</Subscript> and MoO<Subscript>3</Subscript>: Applications to Tribological Systems

Molybdenum disulfide (MoS₂) and molybdenum trioxide are investigated using Raman spectroscopy with emphasis on the application to tribological systems. The Raman vibrational modes were investigated for excitation wavelengths at 632.8 and 488 nm using both micro-crystalline MoS₂ powder and natural MoS₂ crystals. Differences are noted in the Raman spectra for these two different wavelengths, which are attributed to resonance effects due to overlap of the 632.8 nm source with electronic absorption bands. In addition, significant laser intensity effects are found that result in laser-induced transformation of MoS₂ to MoO₃. Finally, the transformation to molybdenum trioxide is explored as a function of temperature and atmosphere, revealing an apparent transformation at 375 K in the presence of oxygen. Overall, Raman spectroscopy is an useful tool for tribological study of MoS₂ coatings, including the role of molybdenum trioxide transformations, although careful attention must be given to the laser excitation parameters (both wavelength and intensity) when interpreting Raman spectra.     

Microstructure,chemical composition,wear, and corrosion resistance of FeB–Fe<Subscript>2</Subscript>B–Fe<Subscript>3</Subscript>B surface layers produced on Vanadis-6 steel using CO<Subscript>2</Subscript> laser

The paper presents the study results of laser modification of FeB–Fe₂B surface layers produced on Vanadis-6 steel using pack cementation method. Microstructure, x-ray phase analysis, chemical composition study using wave dispersive spectrometry method, microhardness, corrosion resistance as well as surface condition, roughness, and wear resistance were investigated. The diffusion boronizing processes were performed at 900 °C for 5 h in the EKabor® powder mixture. The boronized layers had a dual-phase microstructure composed of two types of iron borides, FeB and Fe₂B, and their microhardness ranged from 1800 to 1400 HV. The laser surface modification was carried out on specimens after diffusion boronizing process using CO₂ laser with a nominal power of 2600 W. Laser beam power used in this experiment was equal to 1040 W and was constant. While the three values of scanning speed were used: 19, 48, and 75 mm/s. During laser modification, the multiple tracks were made where distance between of axis tracks was equal to 0.5 mm. As a result of this process, microstructure consisted of remelted zone, heat-affected zone, and substrate was obtained. In remelted zone, the boron-martensite eutectic was observed. Boronized layers after laser modification were characterized by the mild gradient of microhardness from surface to the substrate and their value was dependent on the scanning speed used and was between 1700 and 1100 HV. Corrosion resistance tests revealed reducing the current of corrosion in case of laser modification process. Wear resistance of laser modified specimens was improved in comparison to diffusion boronized layers.     

A stabilized pulsed repetition-rate CO<Subscript>2</Subscript> laser for a laser-plasma generator of multiply charged ions

The design of a laser oscillator with a stabilized frequency composition and a stabilized intensity of output radiation is described. The oscillator’s basic component is a TEA CO₂ module pumped by a self-maintained discharge and operating in a repetition-rate mode at a frequency of up to 3 Hz. A circuit for the formation of a self-maintained homogeneous discharge in the working volume of a CO₂ + N₂ + He mixture at atmospheric pressure is the basic component of the gas-discharge module. This circuit is based on the generation of a high-voltage pulse with a special profile, which provides high-reliability excitation of a discharge and pulse-to-pulse reproducibility of the discharge characteristics. The use of a hybrid circuit in the optical oscillator allows selection of a single longitudinal mode in the output radiation spectrum, thus eliminating undesirable interference phenomena, which lead to instability of the instantaneous values of the radiation intensity. During the development of the oscillator, the optimal operating parameters of the hybrid circuit were obtained, which ensure the high quality and reproducibility of the spatiotemporal and energy parameters of laser radiation.     

氟化锂椭圆弯晶分析器的特性及应用

设计了测试能量范围为0.6~6 keV的椭圆弯晶谱仪。此谱仪利用椭圆自聚焦原理,晶体分析器采用氟化锂材料,椭圆焦距为1 350 mm,离心率为0.958 6,布拉格角范围为30~65°。在神光Ⅱ靶室进行了实验,入射激光波长为0.35 μm,激光功率约为1.6×10¹⁴ W/cm²,与厚度为100 μm的钛平面靶法线夹角约为45°。实验结果证实,弯曲的氟化锂晶体具有极佳探测效果,弯晶分析器对波长为0.2~0.35 nm的X射线的分辨率可达500~1 000,同时具有等光程而便于空间分辨测量的优点,在同样距离条件下比平晶分析器高一个数量级的收光效率,故适合于激光等离子体X射线的光谱学研究。     

A new equation of state to predict S-CO<Subscript>2</Subscript> flow with real gas effects

The accuracy of the thermodynamic properties prediction from the different Equation of state (EOS) varies upon the range of temperature and pressure. Despite the variety of EOS available, there is no de facto for selecting an EOS for particular computational modeling. The EOS model recently developed by Kumar and Kim (K-K EOS) determines more accurately the thermodynamic properties of CO₂ than earlier models. In this present study, K-K EOS is successfully implemented in the computational analysis of compressible supercritical CO₂ flow (S-CO₂) in the thermodynamic region near and away from the vapour-liquid critical point. Computational results of SCO₂ flow with the real gas properties predicted with the K-K EOS is compared with Span and Wagner (SW EOS) and ideal EOS.     

The influence of organobentonite clay on CO2 laser grooving of nylon 6 composites

The popular polycaprolactam (polyamide PA6), commonly referred to as nylon 6, widely used as a construction plastic, is not a typical material for micromachining by CO₂ laser vaporization. In this paper, we describe investigations of the pulsed CO₂ laser grooving of both the chemically pure and the organobentonite clay modified nylon 6. Our results indicate that doping of nylon 6 with nanoparticles of organophilized bentonite significantly improves the grooving ability, predictability of the process, and its quality. In order to determine the nature of the changes in the depth and width of the grooves as a function of the laser process parameters, theoretical modeling of the laser grooving of nylon was carried out. The basic parameters of the laser grooving process versus laser beam intensity, pulse repetition rate, scanning speed of the material and various compositions of the organophilized bentonite dopant are presented. Additionally, an example of a three-dimensional engraving/milling of tested materials as well as the impact of doping on the channel profile are examined. The modification of nylon 6 by appropriate doping with bentonite clay radically improves the quality of micromachining with a CO₂ laser.     

A compact frequency-stabilized pulse-periodic waveguide CO2 laser for calibration of wavelength meters

A compact pulse-periodic waveguide CO₂ laser with high-frequency excitation with automatic assignment of the 10P (14) line and stabilization of the emission frequency in the middle of this line using a sealed-off optoacoustic cell, which is filled with a mixture of C₂H₄ (0.1%) and nitrogen, was developed. It is shown that the laser-frequency instability is within 3 MHz, thus meeting the requirements that are imposed on the calibration tools for high-resolution wavelength meters that are similar to WS-6IR.