Development and research of a laser photo-acoustic SF<Subscript>6</Subscript> gas analyzer

An analysis of various optical schemes for the development of a laser SF₆ gas analyzer based on a CO₂ laser operating in free-running mode and a resonant photo-acoustic detector (PAD) is presented. The use of a sealed gas-filled cell to normalize PAD signals on the absorbed power in the cell is suggested. Compensation for the influence of the tuning of the CO₂ laser wavelength near 10.6 μm on measured SF₆ concentration is possible. The results of experimental studies of a laser photo-acoustic SF₆ gas analyzer at various concentrations, including in the air flow, are presented. It is shown experimentally that the relative measurement error of the SF₆ concentration due to the instability of the laser radiation wavelength does not exceed 5% in the range from ~80 ppb to 40 ppm. The limit of the sensitivity of the developed gas analyzer was ~1 ppb SF₆.     

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.     

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.     

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.     

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.     

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。     

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 TEA CO2 laser with a peak radiation power of 100 MW

A high-power pulse-periodic TEA CO₂ laser is used as a component of a long-range mobile differential absorption lidar. In order to reach the ultimate peak generation power, a system for laser excitation with a supply voltage of ±40 kV and efficient preionization was developed, allowing the laser to operate at high pressures of gas mixtures of various compositions. Energy, time, and spatial characteristics of laser radiation were studied. Laser pulses with an energy of >10 J and FWHM duration of ≈30 ns were obtained. The ultimate peak laser radiation power is 100 MW, and the maximum efficiency with respect to the discharge-consumed energy is 12.6%.     

In-process monitoring of the cutting front of CO2 laser cutting with off-axis optical fibre

A new method is presented in this study to test a way that can effectively provide detailed information on the surface morphology during CO₂ laser cutting by directly measuring the emitted light from the cutting front. The system consists of a copper tube, glass fibre, polymer fibre and photodiode sensor. In this study, the laser power was modulated from 50 Hz to 300 Hz to disturb the natural burning cycle during gas assisted CO₂ laser cutting. The optical fibre was set at 75° to the cutting direction. The wave frequency of the detected signal was very close to the striation frequency of the cut surface, which shows that the sensing system designed and developed in this research can effectively in-process monitor the CO₂ laser cutting process.     

Gap-free lap welding of zinc-coated steel using pulsed CO2 laser

CO₂ laser welding of zinc-coated steel sheets in the lap configuration has been a major research effort for the automotive industry for many years. The introduction of a gap between the sheets is one way of solving the zinc gas explosion problem. However, this requires sophisticated clamping devices and spacer materials. A homogeneous gap is therefore difficult to realise in high volume production. This paper describes a simple but useful approach for CO₂ laser welding of zinc-coated steel sheets in the lap configuration. By using a gated pulse mode, a seam welding process is developed that allows zinc-coated materials to be welded in a gap-free, overlap configuration. Laser seam welds in the lap configuration were produced in 0.7 mm-thick steel sheet with 7 μm zinc coating on both sides. A number of pulsed CO₂ laser welding parameters, including peak power, duty cycle, travel speed, pulse repetition rate, and pulse energy, were identified. Furthermore, the effects of pulsed CO₂ laser welding parameters on weldability were also investigated. The study shows that through the proper selection of welding parameters, it is possible to produce visually sound welds where porosity is still unavoidably formed. It was observed that decreasing the welding speed could reduce the porosity within the visually sound welds.     

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.     

POWER RADIO FREQUENCY CIRCUIT DESIGN FOR A SMALL CO2 SLAB WAVEGUIDE LASER

The design, construction, and test of a radio frequency oscillator-amplifier is presented in this paper. The RF circuit is inserted as part of the electrodes of an in-house-built compact CO₂ waveguide laser. Our circuit was designed to have a frequency at 81 MHz and its signal output between 90 W and 150 W. Capacitive discharge is evaluated over a period of time and, after a correct positioning of several inductors parallel-distributed along the laser electrodes, a steady and uniform plasma discharge was created. The overall RF circuit-laser test is done with a typical gas mixture of CO₂-N₂-He with proportion of 1:1:3, correspondingly, and at a final pressure of 40 Torr. Under these conditions, a maximum optical output power greater than 10.7 W was obtained for an input feed RF power of 147 W.     

A Dispersion Interferometer Based on a CO<Subscript>2</Subscript> Laser

A double-pass dispersion interferometer based on a 9.6-μm CO₂ laser with a sensitivity of 〈 n _e l〉_min ∼ 1 × 10¹³ cm⁻² and a temporal resolution of ∼50 μ s, designed to measure linear plasma density, is described. A ZnGeP₂ nonlinear crystal is used as the frequency doubler. The main advantages of the interferometer are its compactness and a low sensitivity to vibrations of optical elements. The interferometer requires no special vibration isolation. Its main components are arranged compactly on an optical bench outside the apparatus, except for a window for radiation injection and a retroreflector; these are mounted on the wall of the experimental facility's vacuum chamber. The advantages of the dispersion interferometer have been demonstrated in an experiment with a gas-dynamic trap. __________ Translated from Pribory i Tekhnika Eksperimenta, No. 5, 2005, pp. 96–106. Original Russian Text Copyright ? 2005 by Solomakhin, Bagryanskii, Voskoboinikov, Zubarev, Kvashnin, Lizunov, Maksimov, Khil'chenko.     

Energy dependence of the relative light output of YAlO<Subscript>3</Subscript>:Ce,Y<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Ce,and YPO<Subscript>4</Subscript>:Ce scintillators

The nonlinear dependence of the relative light output on the energy deposited in single-crystal scintillation materials YAlO₃:Ce (YAP:Ce), Y₂SiO₅:Ce (YSO:Ce), and YPO₄:Ce (YPO:Ce) has been studied. The investigations have been conducted under quasi-monochromatic X-ray excitation in the energy range of 9.5–100 keV. In addition to the standard technique for measuring the nonproportional scintillator response based on the dependence of the full-energy peak position on the energy of incident radiation, a method is proposed for measuring the light output by X-ray fluorescence peaks. Using this method for YAP:Ce, it is possible to investigate the nonlinear dependence of the light output on the photon energy in the energy range of 2–40 keV. Along with this method, the K-dip spectroscopy method has been proposed and tested by measuring the dependence of the relative light output on the electron energy in the range of 0.1–80.0 keV. The processes resulting in the loss of the scintillation material efficiency at a high ionization density are considered.     

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.     

CO2 Laser Processing On Ceramic Substrates Of Light Emitting Diode Assisted By Compressed Gas

The use of ceramic substrates in high power LEDs is becoming increasingly common. However, the brittleness of ceramics makes them difficult to process and susceptible to cracking. This study used a CO₂ laser with auxiliary gas to drill and cut Al₂O₃ and AlN ceramic substrates. The authors investigated the influences of parameters such as auxiliary gas pressure, laser power, repetition rate, and working speed on processing quality, in terms of pattern size, surface roughness, hole taper angle, and fracturing. The experiment results show that Al₂O₃ low-cost processing can be achieved with low laser power and high auxiliary gas pressure. In contrast, AlN has a high melting point and high thermal conductivity, for which lower auxiliary gas pressure is required to ensure high-quality processing.     

CO2 absorption characteristics of nanoparticle suspensions in methanol

Recently there have been growing concerns that anthropogenic carbon dioxide (CO₂) emissions cause the global warming problem. Therefore, the cutting-edge technologies for the reduction, separation and collection of the CO₂ are very important to alleviate this problem. The best methods for reducing the CO₂ emission are to increase the energy efficiency and to remove it from the power plant. The CO₂ absorption from the syngas in the integrated gasification combined cycle (IGCC) might increase the energy efficiency of the power generation systems, which also contribute to mitigate the global warming. In this study, the suspensions of nanoparticles in methanol (called the nanofluid) are developed and estimated to apply it to absorb CO₂ gas in the IGCC systems. The nanofluids are prepared by the ultrasonic treatment and show the good stability. It is found that the CO₂ absorption rate by the nanofluid is enhanced up to ??8.3% compared to the pure methanol.     

A high-voltage power supply of the diagnostic neutral beam injector of the Alcator-Cmod tokamak

A diagnostic neutral beam injector for ensuring the active spectroscopic diagnostics of plasma parameters in the Alcator-Cmod tokamak (Massachusetts Institute of Technology (MIT), Boston, United States) is designed and manufactured at the Institute of Nuclear Physics (Novosibirsk). The energy of fast atoms of the diagnostic injector is determined by the output voltage level of the high-voltage power supply and can vary from 20 to 55 keV. The ion source of the diagnostic neutral beam injector generates proton beams with an equivalent current of up to 7 A. The accelerated protons after the neutralization on a gas target produce streams of neutral particles—fast atoms with an equivalent current of up to 4 A. The diagnostic neutral beam injector is capable of producing 100% energy-modulated fast hydrogen atomic beams, and this is ensured by operation of the high-voltage power supply under the corresponding law. The high-voltage power supply is based on modules consisting of high-frequency transformers and diode rectifiers placed in a sealed tank filled with insulating gas SF₆. The output voltage is smoothly regulated from 20 to 55 kV by IGBT inverters with a pulse-width control energizing the primary windings of the step-up high-frequency transformers. The high-voltage power supply allows the multiple-breakdown operation mode of the load with voltage recovering as the specified time passes after the breakdown. The rated power of the high-voltage power supply is 450 kW. A functional diagram and design of the high-voltage power supply are given.     

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.