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.     

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.     

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.     

Investigation of Annealing Temperature on Structural and Morphological Properties of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticles for Humidity Sensor Application

Cr₂O₃ nanoparticles have been prepared for precipitation technique at reaction temperature 50 °C. The prepared samples were annealed different temperatures at 500,700 and 1000 °C. Synthesized powders were characterized as X-ray diffraction, optical, transmission electron microscope, SEM with EDAX, humidity sensor, FTIR. The annealing temperature has been found to be playing a crucial role in the controlling particle size. XRD study shows the rhombohedral crystal structure of highly preferential orientation along (1 0 4) direction. FTIR reveals that the presence Cr–O bonds in the structure. The TEM images show that the size of NPs of Cr₂O₃ varied from 26 to 60 nm with average crystalline size 43 nm. UV–visible spectrum shows the absorption band of Cr₂O₃ nanoparticles at 400 nm. The humidity sensor of the Cr₂O₃ nanoparticles was studied by two temperature method. 1000 °C annealed Cr₂O₃ nanoparticles show better sensing properties and exhibits good linearity in response than 500 °C. SEM images show the clusters and agglomeration of nanoparticles. EDAX spectrum confirms the presence of Cr₂O₃ nanoparticles. Each samples have been characterized as sensing materials to determine relative humidity in the range of 20–90%. The humidity sensing property increased with increasing of annealing temperature and the resistance was decreased.     

Effect of Atmosphere and Temperature on the Tribological Behavior of the Ti Containing MoS<Subscript>2</Subscript> Coatings Against Aluminum

MoS₂ coatings exhibit low coefficient of friction (COF) when sliding against aluminum; however, the magnitudes of their COF show high sensitivity to environmental conditions. Ti could reduce the sensitivity of the frictional behavior of MoS₂ coatings to moisture. This study examines the tribological properties of Ti containing MoS₂ coating (Ti–MoS₂) tested against an aluminum alloy (Al-6.5% Si) in ambient air (58% relative humidity, RH), dry oxygen, dry air and dry N₂ (< 4% RH) atmospheres. The Ti–MoS₂ coating exhibited similar COF values under an ambient (0.14), dry oxygen (0.15) and dry air (0.16) atmospheres. It was found that oxidation of MoS₂ to MoO₃ was responsible for high COF under these testing conditions as revealed by Energy-dispersive X-ray Spectroscopy (EDS) and micro-Raman spectroscopy. However, a low and stable COF of 0.07 was observed under a dry N₂ condition. This work further showed that the tests performed at elevated temperatures, up to 400 °C in a dry N₂ atmosphere sustained the low and stable COF of the Ti–MoS₂ coatings. The sliding tests performed under a dry N₂ atmosphere prevented the formation of MoO₃ and as a result, the Ti–MoS₂ coatings maintained low COF values. Low COF values were also attributed to the formation of MoS₂ transfer layers.     

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.     

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 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.     

A neutron semiconductor detector based on TIInSe<Subscript>2</Subscript>

A new semiconductor detector of neutron radiation based on a TIInSe₂ crystal has been investigated. The detector is produced from a homogeneous semiconductor sample with two electric contacts and operates in an integrating mode. It is shown that, owing to its high sensitivity (～10^?13 A/(neutron cm^?2 s^?1)) and small size (the volume of the sensitive crystal element is ～7 mm³), the detector is capable of monitoring spatial, time, and intensity distributions of γ rays and neutrons in pulse research reactors.     

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.     

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.     

Wear Behaviour of In Situ Al/TiB<Subscript>2</Subscript> Composite: Influence of the Microstructural Instability

In this present work, the in situ Al (A380)/5 wt%TiB₂ composites were fabricated through salt–melt reaction using halide salts such as potassium hexafluorotitanate (K₂TiF₆) and potassium tetra fluoroborate (KBF₄) salts as precursors. The composites were produced at four different melt temperatures (700, 750, 800, 850 °C). The formation of particle was confirmed from XRD results. The wear behaviour of Al/5 wt% TiB₂ composite was investigated by varying the wear test parameters such as sliding temperature (25, 100, 150, 200 °C), applied load (10, 20, 30, 40 N), sliding velocity (0.4, 0.7, 1, 1.3 m/s). The microstructure of Al/5 wt% TiB₂ composite was correlated with the wear characteristics of the composites. The wear resistance of Al/5 wt% TiB₂ composite was significantly improved due to the presence of TiB₂ particle in Al matrix material. The composite produced at melt temperature 800 °C showed a higher wear resistance at applied load: 10 N, sliding temperature: 25 °C and sliding velocity: 0.7 m/s. The wear mechanism for each of the tested condition was identified from the worn surfaces using scanning electron microscopy (SEM). ANOVA test was carried out to find out significant factor for the wear resistance of composite. The checking of adequacy of experimental value for the wear behaviour of composite for different testing condition was analysed by residual plots using statistical software.     

Tribological Property of Ni<Subscript>3</Subscript>Al Matrix Composites with Addition of BaMoO<Subscript>4</Subscript>

The Ni₃Al matrix composites with addition of 10, 15, and 20 wt% BaMoO₄ were fabricated by powder metallurgy technique, and the tribological behaviors were studied from room temperature to 800 °C. It was found that BaAl₂O₄ formed during the fabrication process. The Ni₃Al composites showed poor tribological property below 400 °C, with high friction coefficients (above 0.6) and wear rates (above 10⁻⁴ mm³/Nm). However, the composites exhibited excellent self-lubricating and anti-wear properties at higher temperatures, and the composite with addition of 15 wt% BaMoO₄ had the lowest wear rate (1.10 × 10⁻⁵ mm³/Nm) and friction coefficient (0.26). In addition, the results also indicated that BaAl₂O₄ for the Ni₃Al composites did not exhibit lubricating property from room temperature to 800 °C.     

Synergistic Effect of Nano-MoS<Subscript>2</Subscript> and Anatase Nano-TiO<Subscript>2</Subscript> on the Lubrication Properties of MoS<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> Nano-Clusters

A MoS₃ precursor deposited on anatase nano-TiO₂ is heated at 450 °C in an H₂ atmosphere to synthesize MoS₂/TiO₂ nano-clusters. The nano-clusters are then characterized, and their tribological properties are evaluated. MoS₂ is found to be composed of layered structures with 1–10 nm thicknesses, 10–30 nm lengths, and 0.63–0.66 nm layer distances. The MoS₂ sizes in the MoS₂/TiO₂ nano-clusters are smaller and their layer distances are larger than those of pure nano-MoS₂. The MoS₂/TiO₂ nano-clusters also present a lower average friction coefficient than pure nano-MoS₂, but the anti-wear properties of both the nano-clusters and pure nano-MoS₂ are similar. X-ray photoelectron spectroscopy indicates that nano-TiO₂ and the element Mo are transferred to the friction surface from the MoS₂/TiO₂ nano-clusters through a tribochemical reaction. This produces a lubrication film containing TiO₂, MoO₃, and other chemicals. The nano-MoS₂ changes in size and layer distance when combined with nano-TiO₂, producing a synergistic effect. This may further be explained using a micro-cooperation model between MoS₂ nano-platelets and TiO₂ solid nanoparticles.     

Effects of ZnO and MoS<Subscript>2</Subscript> Solid Lubricants on Mechanical and Tribological Properties of M50-Steel-Based Composites at High Temperatures: Experimental and Simulation Study

Prospective beneficial effects of mixtures of temperature-adaptive solid lubricants (ZnO–MoS₂) on mechanical and tribological properties of M50 alloy steel were investigated at temperatures from 25 to 800 °C. ZnO and MoS₂ were mixed with M50 (designated as M) to create composites MZ (M50 steel plus ZnO), MM (M50 steel plus MoS₂), and MZM (M50 steel plus both additives). Sliding friction and wear experiments were performed at different temperatures using a pin-on-disk at a sliding speed of 0.2 m s^?1 and a load of 12 N. Silicon nitride and M50 steel were used as the pin materials. In order to understand the friction and wear behavior of composites, analyses of their surfaces were done using XRD, EPMA, FESEM, EDS line/mapping, and XPS tests. A dynamic simulation model based on the finite element method was built to simulate the different stresses on the contact pairs. Results elucidated that MZM attained the least friction (0.17), compared to M (0.40), MZ (0.26), or MM (0.29) at 800 °C. The increase in surface roughness of MZM due to sliding was reduced by 37.3% compared to that of MZ (11.9%) or MM (22.7%). The good lubricating behaviors were referred to the synergetic effects of ZnO, MoS₂, and formed lubricating components on worn surfaces.     

Abrasive and Adhesive Wear Behavior of Arc-Evaporated Al<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N Hard Coatings

During the last decade, the usage of difficult-to-machine materials such as austenitic stainless steels has increased continuously in various industrial applications. Tools such as blind hole taps, punches, or deep drawing molds are often exposed to severe wear while machining/forming these materials, mainly due to excessive adhesion and material transfer. On combination with abrasive wear due to work-hardened wear debris, tool lifetime in these applications is often limited. In this study, ball-on-disc experiments were carried out with arc-evaporated AlCrN coatings with different Al/(Al + Cr) ratios against Al₂O₃ and austenitic stainless steel balls in ambient atmosphere. Test temperatures of 25, 500, and 700°C were chosen for the hard Al₂O₃ balls simulating severe abrasive loads, whereas 25, 150, and 250°C were used for the softer stainless steel material to evaluate the adhesive wear behavior. Characterization of the wear tracks was done by scanning electron microscopy in combination with energy-dispersive X-ray analysis and optical profilometry. The best abrasive wear resistance during testing against Al₂O₃ was observed for the coating with the highest Al content. In the case of the austenitic stainless steel balls, sticking of the ball material to the coating surface was the dominating wear mechanism. The influence of test temperature, chemical composition, and surface roughness was studied in detail.     

Growing HgTe/Cd<Subscript>0.735</Subscript>Hg<Subscript>0.265</Subscript>Te quantum wells by molecular beam epitaxy

HgTe/Cd_0.735Hg_0.265Te nanostructures with HgTe quantum wells 16.2 and 21.0 nm thick are grown without additional doping on (013)CdTe/ZnTe/GaAs substrates by the method of molecular beam epitaxy. The compositions and thicknesses of the wide-gap layer and quantum well in the course of growth are performed by means of ellipsometry. The accuracy is Δx ? ±0.002 mole fractions of cadmium telluride in determining the composition and Δd ? 0.5 nm in determining the thickness of the wide-gap layer and quantum well. The central fragments of the wide-gap layers ≈ 10 nm thick are additionally doped by indium for a ～ 10¹⁵ cm^?3 volume concentration of charge carriers to be reached. Galvanomagnetic research in a wide range of magnetic field intensities at liquid helium temperatures reveals dimensional quantization levels and the presence of a two-dimensional electron gas in grown nanostructures. High mobility of the two-dimensional electron gas μ _e is obtained: 2 · 10⁵ and 5 · 10⁵ cm²/V · s for electron densities N _s equal to 1.5 · 10¹¹ and 3.5 · 10¹¹ cm^?2, respectively.     

The Tribological Mechanism of MoS<Subscript>2</Subscript> Film under Different Humidity

Molybdenum disulfide (MoS₂) has been widely used in vacuum environment as an excellent solid lubricant. However, the application of MoS₂ is greatly limited in terrestrial atmosphere due to the sensitivity to humidity. Although the sensitivity of MoS₂ to water vapor has been widely recognized, the mechanism is not clear. To explore the tribological mechanism of MoS₂ in the presence of water vapor, a series of experiments were performed to investigate the effect of N₂ (inert gas), O₂ (active gas), air (a combination of both) and cyclic humidity change in air on the frictional response of MoS₂ to humidity. According to the results, a model that described water adsorption enhanced by active sites in MoS₂ and formed oxides, and an adsorption action change in water molecules with humidity was proposed. The model was applied to explain the recovery and instantaneous response of friction coefficient to humidity change.     

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.