Evaluation of fracture toughness of ZrO2 and Si3N4 engineering ceramics following CO2 and fibre laser surface treatment

The fracture toughness property (K_1C) of Si₃N₄ and ZrO₂ engineering ceramics was investigated by means of CO₂ and a fibre laser surface treatment. Near surface modifications in the hardness were investigated by employing the Vickers indentation method. Crack lengths and the crack geometry were then measured by using the optical microscopy. A co-ordinate measuring machine was used to investigate the diamond indentations and to measure the lengths of the cracks. Thereafter, computational and analytical methods were employed to determine the K_1C. An increase in the K_1C of both ceramics was found by the CO₂ and the fibre laser surface treatment in comparison to the as-received surfaces. The K_1C of the CO₂ laser radiated surface of the Si₃N₄ was over 3% higher in comparison to that of the fibre laser treated surface. This was by softening of the near surface layer of the Si₃N₄ which comprised of lowering of hardness, which in turn increased the crack resistance. The effects were not similar in ZrO₂ ceramic to that of the Si₃N₄ as the fibre laser radiation in this case had produced an increase of 34% compared to that of the CO₂ laser radiation. This occurred due to propagation of lower crack resulting from the Vickers indentation test during the fibre laser surface treatment which inherently affected the end K_1C through an induced compressive stress layer. The K_1C modification of the two ceramics treated by the CO₂ and the fibre laser was also believed to be influenced by the different laser wavelength and its absorption co-efficient, the beam delivery system as well as the differences in the brightness of the two lasers used.     

Measurements and assignments of new large offset CD3OH FIR laser lines

By using an acoustooptic modulator we extend the 300 MHz tunability of a waveguide CO₂ laser to 480 MHz. The CD₃OH was optically pumped by the 10R(32), 10R(34), and 10R(36) CO₂ laser lines, and 17 new FIR laser lines were discovered. The Stark effect on previously known FIR laser lines was investigated, and some tentative FIR laser lines assignments are suggested.     

Laser surface remelting of plasma sprayed nanostructured Al2O3-13wt%TiO2 coatings on titanium alloy

Plasma sprayed nanostructured coatings were successfully fabricated on a titanium alloy (Ti-6Al-4V) substrate using the as-prepared nanostructured Al₂O₃-13wt%TiO₂ feedstock. A CO₂ laser was used to remelt the plasma sprayed coatings. The effects of laser remelting on the phase constituents, microstructure and properties of the ceramic coatings were investigated. The laser remelted coatings (LRmC) possessed a much denser and more homogenous structure and excellent metallurgical bonding to the substrate. The average porosity of the LRmC was reduced to 0.9%, compared with 6.2% of the as-sprayed coatings. The net-like structure in the as-prepared feedstock remained in the coatings before and after laser remelting. The metastable γ-Al₂O₃ phase in the as-sprayed coatings transformed to stable α-Al₂O₃ during laser remelting. The LRmC could remain nanostructure. The microhardness of the coatings was enhanced to 1000-1400 HV_0.3 after laser remelting, which was much higher than that of the plasma sprayed coatings and 2-3 times higher that of the substrate. Significant decreases in surface roughness were also found in the LRmC.     

Microstructure of laser melted Al18B4O33w/2024Al composite

The microstructure of a laser treated Al₁₈B₄O₃₃w/2024Al composite has been investigated using transmission electron microscope (TEM), low-angle (glancing angle) X-ray diffraction (XRD) techniques. Various surface microstructures were observed in the laser treated composite. The Al₁₈B₄O₃₃ whisker on the surface of the composite was decomposed during laser surface melting, various decomposition products were studied in the laser treated composite. Eutectic phases and the precipitation in the matrix of the composite with laser-treated were observed. The main phases detected in the molten zone were aluminum and decomposition products Al₂O₃. The effect of laser treatment on the hardness of the composite was also examined. A surface hardness of 400 Hv was noted.     

CO2 laser assisted removal of UO2 and ThO2 particulates from metal surface

Pulsed laser assisted removal of uranium dioxide and thorium dioxide particulates from stainless steel surface have been studied using a TEA CO₂ laser. Decontamination efficiency is measured as a function of laser fluence and number of pulses. Threshold fluence for the removal of UO₂ particulates has been found to be lower than that required for the removal ThO₂ particulates. Usage of a ZnSe substrate, that is transparent to the laser wavelength used here, enabled us to decouple the cleaning effect arising out of absorption in the particulates from that in the substrate and has contributed towards understanding the mechanism responsible for cleaning. The experimental observations are also corroborated by simple theoretical calculations.     

Investigation of cutting of engineering ceramics with Q-switched pulse CO2 laser

In this paper, the cutting of Si₃N₄ engineering ceramics with Q-switched pulse CO₂ laser is studied. Considering the influence of the cut front shape on the absorption of the laser beam, a simplified 2D mathematic model is developed based on a pulsed laser vaporization cut process. This model is based on the conservation of energy. The experimental results show that it would realize crack-free cutting by using high-speed and multi-pass feed cutting process.     

New Far-Infrared Laser Lines and Frequency Measurements of Acetaldehyde and Vinyl Fluoride

Eight far-infrared laser lines have been obtained by optically pumping acetaldehyde (CH₃CHO) and nine by pumping vinyl fluoride (CH₂CHF) with a cw CO₂ laser. The far-infrared laser structure used a metal-dielectric waveguide cavity. This is the first reported observation of four of the laser lines in acetaldehyde. In this work, we measure the frequency, optimum pressure of operation, relative intensity, relative polarization, and pump offset from CO₂ laser-line center.     

Optical characteristics of amorphous V2O5 thin films colored by an excimer laser

The V₂O₅ films were prepared by an RF sputtering method, and the amorphous films were colored by an UV excimer laser. The crystallinity of the as-grown V₂O₅ film was degenerated greatly by laser irradiation, as determined by X-ray diffraction (XRD) and Raman studies. The transmission and complex refractive index spectra of the V₂O₅ film were affected by variations in the microstructure, including the surface morphology, crystalline structure, and substoichiometry with an oxygen deficiency. Considerable emissions due to oxygen vacancies and band transition of photoluminescence (PL) peaks were observed, and the peaks were significantly changed after laser irradiation. The variations in the optical properties in both films may be attributed to oxygen deficiency induced by laser irradiation.     

非晶Fe73.5Cu1Nb3Si13.5B9合金激光纳米化的超精细结构研究

在CO₂激光功率为50—300W、扫描速度为20mm/s、激光散光斑为20mm照射条件下 ，诱导非 晶Fe_735Cu₁Nb₃Si_135B9带中发生结构重组，产生定量纳米α-F e(Si)晶相形成双相组织结构材料. 利用穆斯堡尔谱研究了非晶Fe_735C u₁Nb₃Si_135B₉合金激光纳米化的 超精细结构. 实验结果表明，激光诱导非晶 Fe_735Cu₁Nb₃Si_135B ₉纳米化后，其超精细磁场的分布随 着激光功率变 化由单峰向双峰变化，在高功率辐照时， 出现了双峰分布，并且峰位向高场移动. 高激光 功率辐照非晶Fe_735Cu₁Nb₃Si_{135B9合金纳米晶化相有四种超精细结 构，即2个超精细磁场较小的初晶相和2个超精细磁场较大的纳米晶化相. 其中超精细磁场较 大(17—25MA/m)的α-Fe(Si)相为DO3结构. 关键词： 激光 纳米晶α-Fe（Si) 735}Cu₁Nb< sub>3Si_135B₉')" href="#">非晶Fe_735Cu₁Nb< sub>3Si_135B₉ 超精细结构 超精细磁场     

Acoustooptic extension of the frequency tunability of CW CO2 lasers: New FIR lasers emissions from CH3OH and13CH3OH

We have increased the frequency tunability of our CW waveguide CO₂ lasers by means of an acoustooptic amplitude modulator, operating at the fixed frequency of 90 MHz. The up-shifted, or down-shifted, laser optical sideband can be generated independently by adjusting the orientation of the modulator. The efficiency is larger than 50%. The frequency tunability of the CO₂ laser around each laser line is thus increased by 180 MHz. To demonstrate the possibilities of this method, a source composed of the above modulator and of a CW, 300 MHz tunable waveguide CO₂ laser has been used for the search of new large offset FIR laser lines from optically pumped CH₃OH and¹³CH₃OH molecules. As a result 15 and 10 new large offset laser lines were discovered respectively. New assignments of some laser lines are also proposed. We have also measured the Stark effect, the offset, and the polarization of other already known lines. In particular a Stark effect frequency tuning of about 1 GHz is demonstrated for a laser line at 208.399 m.     

Surface evolution and laser damage resistance of CO2 laser irradiated area of fused silica

A 10.6 μm CO₂ laser has been reported to effectively mitigate the laser damage growth of fused silica. Two zones of the laser irradiated area are defined in this work: the distorted zone and the laser affected zone. The parameters of the two zones are studied at different CO₂ laser beam sizes, irradiation times, and powers by microscopy, profilometry, and photoelastic method. The results show that the diameter of laser affected zone is almost completely determined by the laser beam size and the distorted zone is associated with the mitigation range of CO₂ laser beam. The diameter and depth of the distorted zone increase as the laser power and irradiation time increase. The depth grows exponentially depending on the irradiation time. The maximum residual stress discrepancy is located near the boundary of the laser affected zone. The laser damage resistance test results show that the distorted zone and the laser affected zone have a better damage resistance than the original substrate.     

Effects of some synthesis parameters on the structure of titania nanoparticles obtained by laser pyrolysis

The preparation of TiO₂ nanoparticles by CO₂ laser pyrolysis of TiCl₄ (vapor)-based gas mixtures was investigated as a function of laser power and influence of the oxidizer. Increased crystallinity and crystallite dimensions as well as increase of the rutile fraction are observed at moderate flow increase in the flow rate of the oxidizing agent.     

Intracavity-frequency-doubled Q-switched and mode-locked Nd:Lu0.15Y0.85VO4/KTP green laser with AO modulator and central SESAM

By using mixed crystal Nd:Lu_0.15Y_0.85VO₄ as laser medium, KTP as frequency-doubling crystal, a diode-pumped intracavity-frequency-doubled Q-switched and mode-locked (QML) Nd:Lu_0.15Y_0.85VO₄/KTP green laser with acousto-optic (AO) modulator and central semiconductor saturable absorption mirror (C-SESAM) is realized by using a V-type cavity. The QML laser characteristics such as the pulse width, single-pulse energy, have been measured for different modulation frequencies of the AO modulator. In comparison with the singly passively QML green laser with central SESAM, the doubly QML green laser can generate more stable and shorter pulses with higher peak power. Based on the coupled rate equations for a diode-pumped doubly QML green laser with AO and C-SESAM, in which the saturated absorption mechanism of C-SESAM is considered, the recurrence relation of the relative amplitude of the mode-locking pulses is given and the related numerical simulations are in good agreement with the experimental results.     

New FIR laser lines from optically pumped C2H3F, C2H3Cl, C2H3Br, C2H3CN, C2H5F, CH2CF2, HCOOH and CH3Br

Twenty-seven new cw far infrared laser lines with wavelengths between 137 and 988m have been observed from optically pumping C₂H₃F, C₂H₃Cl, C₂H₃Br, C₂H₅F, C₂H₃CN, CH₂CF₂, HCOOH and CH₃Br with a CO₂ laser. The wavelengths of these FIR laser lines were determined together with their optimum pressures and relative intensities.     

Examination of temperature distribution and the thermal effects on Si3N4 engineering ceramics during fibre laser surface treatment

The thermal effects of fibre laser surface treatment on a Si₃N₄ engineering ceramic were studied using a computational finite element analysis (FEA). Temperature increases on the surface of the Si₃N₄ during fibre laser processing were measured using an infra-red thermometer; temperature distributions in the bulk were measured with specifically located thermocouples. A computational model by using FEA was then developed to model the flow and the distribution of the radiated heat resulting from the fibre laser treatment of the Si₃N₄ ceramic. By utilising data obtained from a TG-DSC analysis the FEA model predictions of the temperature distribution were used to map phase transformations and significant events occurring during the fibre laser surface treatment of the Si₃N₄. The TG-DSC analysis also indicated that the fibre laser surface treatment generally resulted in a phase transformation of the Si₃N₄ from α-phase to β-phase modification as elongated rod-like grains were found.     

Optimization of three gas compositions in a CO2 laser

Three pressures of gases (CO₂, N₂ and He) added into CO₂ laser tube are optimized for obtaining maximal laser output power by applying a genetic algorithm and solving the CO₂ laser kinetics equations. After the optimization, the laser power is increased by 96% as compared with a non-optimal case.     

Optically pumped submillimeter laser lines from CD2Cl2 using a large tunability CW CO2 laser

Twenty-five new laser lines have been obtained in the wavelength region from 155 to 830 μm by optically pumping the CD₂Cl₂ (deuterated dichloromethane) molecule with a CW CO₂ laser having a tunability range of 300 MHz. The wavelength, polarization relative to that of CO₂ pumping radiation, and offset relative to the CO₂ center frequency were determined for all of the new lines and some other already known laser emissions. For all of them we give also the relative intensity and the optimum pressure of operation. Permanent address: Depto de Física e Química da FEIS — UNESP 15.378-000 Ilha Solteira-SP, Brazil     

The thermal effect in diode-end-pumped continuous-wave 914-nm Nd:YVO4 laser

The thermal effect and the heat generation in diode-end-pumped continuous-wave 914-nm Nd:YVO₄ lasers are investigated in detail. A theoretical model of a diode end-pumped solid-state laser is constructed to analyse the influence of fractional thermal loading on the thermal effect in the Nd:YVO₄ laser based on finite element analysis. The thermal focal lengths and the end-surface deformations of laser rods in Nd:YVO₄ quasi-three-level and four-level lasers are measured and compared with the results obtained by ordinary interferometry for the demonstration of higher thermal loading in 914-nm laser. Finally the fractional thermal loading in the Nd:YVO₄ quasi-three-level laser is calculated by matching the experimental and the simulated end deformations.     

Laser synthesis of thin layers of In4Se3, In4Te3 and modification of their structure and characteristics

Trends of structural modifications and phase composition occurring in In₄Se₃ thin films and In₄Se₃-In₄Te₃ epitaxial heterojunctions under laser irradiations have been investigated. Dynamics of the layer structure modification, depending on laser modes, i.e. pulse duration τ = 2-4 ms, irradiation intensity I₀ = 10-50 kW/cm², number of pulses N = 5-50, was studied by electron microscopy. An increase in laser influence promotes enlargement of the layer grains and transformation of their polycrystalline structure towards higher degree of stoichiometry. As a result of laser solid restructuring heterojunctions of In₄Se₃-In₄Te₃, being photosensitive within 1.0-2.0 μm and showing fast time of response, have been obtained. Laser modification of structure enables one to optimize electrical and optical properties of functional elements on the base of thin films and layers of In₄Se₃, In₄Te₃, widely used as infrared detectors and filters.     

An injection-locked single-mode tea CO2 laser for SMM laser pumping

A D₂O laser has been developed for collective Thomson scattering measurements of ion temperature in high temperature plasmas. A pulse duration and a spectral width of a high power D₂O laser has been successfully controlled for this purpose, by using a TEA CO₂ laser injection-locked by an etalon-tuned TEA CO₂ laser as a pump source.