High-quality and high-efficiency machining of glass materials by laser-induced plasma-assisted ablation using conventional nanosecond UV, visible, and infrared lasers

This paper reports the micromachining of fused quartz and Pyrex glass by laser-induced plasma-assisted ablation (LIPAA) using a conventional nanosecond laser at wavelengths 266 nm, 532 nm, and 1064 nm, respectively. High-quality surface structuring can be achieved at each of these wavelengths. The micrograting formed has periods of 14 7m at 266 nm, 20 7m at 532 nm, and 30 7m at 1064 nm, respectively. The ablation rate using a 266 nm laser is much larger than that at longer wavelengths. The ablation thresholds of laser fluence are 0.7 J/cm² for 266 nm, 1.5 J/cm² for 532 nm and 3.7 J/cm² for 1064 nm, respectively. The 532 nm and 1064 nm lasers enable hole drilling in 0.5 and 2.0-mm thick fused quartz and Pyrex glass substrates of about 0.7-0.8 mm in diameter. However, the less destructive through channel can be only formed in Pyrex glass by using a 532 nm laser.     

Laser Induced Breakdown Spectroscopy for Comparative Quantitative Analysis of Betel Leaves from Pakistan

Laser induced breakdown Spectroscopy (LIBS) was applied for the elemental analysis and exposure of the heavy metals in betel leaves in air. Pulsed Nd∶YAG (1064 nm) in conjunction with a suitable detector (LIBS 2000+, Ocean Optics, Inc) having the optical resolution of 0.06 nm was used to record the emission spectra from 220 to 720 nm. Elements like Al, Ba, Ca, Cr, Cu, P, Fe, K, Mg, Mn, Na, P, S, Sr, and Zn were found to present in the samples. The relative abundances of the observed elements were calculated through standard calibration curve method, integrated intensity ratio method, and weight percentage LIBS approach. LIBS findings were validated by comparing its results with the results obtained using a typical analytical technique of Inductively Coupled plasma-optical emission spectroscopy (ICP-OES). Limit of detection (LOD) of the LIBS system was also estimated for heavy metals. The experience gain through this work implies that LIBS could be highly applicable for testing the quality and purity of food products.     

Determination of the ratio of soot refractive index function E(m) at the two wavelengths 532 and 1064 nm by laser induced incandescence

A new method is proposed to measure the ratio of the refractive index function of soot particles E(m) at the two fixed wavelengths: 532 and 1064 nm. Using a non-intrusive, in-situ laser based technique, the ratio E(m,1064 nm)/E(m,532 nm) can be determined by comparing laser induced incandescence (LII) intensities at 532 and 1064 nm excitation wavelengths. The method consists of selecting laser energies that insure the equality of the LII signals in the low fluence regime under given conditions. Such equality is consistent with the fact that the soot particle will have reached the same temperature independently of the laser wavelength, i.e. the soot particle has absorbed the same energy. As the absorbed energy is proportional to the laser irradiance times E(m), the measurement of the laser energies required to insure perfect concordance of the LII intensities (spatially and temporally) serves to deduce the ratio E(m,1064 nm)/E(m,532 nm). The method is demonstrated in an acetylene/air flame, validated against extinction measurements performed by cavity ring-down spectroscopy (CRDS) by using laser radiations at 532 nm and 1064 nm and finally applied to different flame conditions. PACS 78.20.Ci; 78.90.+t; 81.05.Uw; 42.62.-b     

Optical studies on the deposition of carbon nitride films by laser ablation

2 radicals when the 355 and 1064 nm outputs of a Nd:YAG laser were applied. While for the 532 nm ablation, a relatively higher concentration of excited atomic carbon was obtained. Different Raman and FTIR spectral features were observed from the deposited films with different ablation wavelengths. The 532 nm laser ablation is proposed for the synthesis of high quality carbon nitride films. Received: 16 October 1996 / Accepted: 11 April 1997     

Two-dimensional measurements of laser-induced breakdown in air by high-speed two-frame shadowgraphy

We present two-dimensional measurements of the laser-induced plasma development and shock wave evolution in air. The breakdown is induced by a Q-switched Nd:YAG laser (λ=1064 nm) with a pulse duration of 4 ns. To study these fast laser-induced phenomena, we have developed a high-speed, two frame shadowgraph method. It enables 2D visualization of a laser-induced event in two time instances, which are delayed by an arbitrary time interval in the range from 300 ps to 30 ns. The established method is based on 30 ps, green (λ=532 nm), and linearly polarized laser pulse, which is split into two orthogonally polarized illumination pulses for direct and delayed illumination of the breakdown area. Exploiting polarization of the probe pulses, we capture two temporally and spatially separated frames with two CCD cameras. Special attention is given to the subsequent data processing, especially to the minimization of the systematic error due to alignment of both images, and to the determination of 2D velocity distribution from the captured image pairs.     

土壤中重金属元素的双脉冲激光诱导击穿光谱研究

基于正交预烧蚀双脉冲激光诱导击穿光谱(DP-LIBS) 技术对长春市四个地点地表土壤样品中的重金属元素进行了研究, 根据光谱线强度定性分析了重金属元素Mn, Cr, Cu, Pb含量.实验结果发现, 在532和1064 nm激光脉冲能量分别为70和100 mJ的条件下光谱增强随延时的变化出现双峰结构. 脉冲间延时20 μs时, Mn I 406.4 nm光谱增强幅度达到2.75倍, 延时为30 μs时出现第二个尖峰, 增强幅度为2.4倍.最后对正交预烧蚀DP-LIBS光谱增强机理进行了讨论. 关键词： 预烧蚀 双脉冲激光诱导击穿光谱 光谱增强 土壤污染     

Enhanced optical limiting effect in fluorine-functionalized graphene oxide

Nonlinear optical absorption of fluorine-functionalized graphene oxide (F-GO) solution was researched by the open-aperture Z-scan method using 1064 and 532 nm lasers as the excitation sources. The F-GO dispersion exhibited strong optical limiting property and the fitted results demonstrated that the optical limiting behavior was the result of a two-photon absorption process. For F-GO nanosheets, the two-photon absorption coefficients at 1064 nm excitation are 20% larger than the values at 532 nm excitation and four times larger than that of pure GO nanosheets. It indicates that the doping of fluorine can effectively improve the nonlinear optical property of GO especially in infrared waveband, and fluorine-functionalized graphene oxide is an excellent nonlinear absorption material in infrared waveband.     

Surface modifications of AISI 1045 steel created by high intensity 1064 and 532 nm picosecond Nd:YAG laser pulses

Interaction of Nd:YAG laser, operating at 1064 or 532 nm wavelength and a pulse duration of 40 ps, with AISI 1045 steel was studied. Surface damage thresholds were estimated to be 0.30 and 0.16 J/cm² at the wavelengths of 1064 and 532 nm, respectively. The steel surface modification was studied at the laser energy density of 10.3 J/cm² (at 1064 nm) and 5.4 J/cm² (at 532 nm). The energy absorbed from Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following AISI 1045 steel surface morphological changes and processes were observed: (i) both laser wavelengths cause damage of the steel in the central zone of irradiated area; (ii) appearance of a hydrodynamic feature in the form of resolidified droplets of the material in the surrounding outer zone with 1064 nm laser wavelength; (iii) appearance of periodic surface structures, at micro- and nano-level, with the 532 nm wavelength and, (iv) development of plasma in front of the target. Generally, interaction of laser beam with the AISI 1045 steel (at 1064 and 532 nm) results in a near-instantaneous creation of damage, meaning that large steel surfaces can be processed in short time.     

可溶性碳纳米管光限幅特性的实验研究

利用实验的方法研究了可溶性碳纳米管对波长为1064和532nm激光的光限幅效应.分析了在 不同的样品浓度、不同的样品厚度情况下可溶性碳纳米管的光限幅特性，并对溶剂也进行了 光限幅实验.实验结果表明，在各种情况下可溶性碳纳米管对1064和532nm激光具有较强的 光限幅特性. 关键词： 可溶性碳纳米管 光限幅效应 强激光防护     

Processing of Diamond for Integrated Optic Devices Using Q-Switched Nd:YAG Laser at Different Wavelengths

In the present investigation, a Q-switched Nd:YAG laser is used to study the various aspects of diamond processing for fabricating integrated optic and UV optoelectronic devices. Diamond is a better choice of substrate compared to silicon and gallium arsenide for the fabrication of waveguides to perform operations such as modulation, switching, multiplexing, and filtering, particularly in the ultraviolet spectrum. The experimental setup of the present investigation consists of two Q-Switched Nd:YAG lasers capable of operating at wavelengths of 1064 nm and 532 nm. The diamond cutting is performed using these two wavelengths by making the “V”-shaped groove with various opening angle. The variation of material loss of diamond during cutting is noted for the two wavelengths. The cut surface morphology and elemental and structural analysis of graphite formed during processing in both cases are compared using scanning electron microscopy (SEM) and laser Raman spectroscopy. Both the Q-Switched Nd:YAG laser systems (at 1064 nm and 532 nm) show very good performance in terms of peak-to-peak output stability, minimal spot diameter, smaller divergence angle, higher peak power in Q-switched mode, and good fundamental TEM₀₀ mode quality for processing natural diamond stones. Less material loss and minimal micro cracks are achieved with wavelength 532 nm whereas a better diamond cut surface is achieved with processing at 1064 nm with minimum roughness.     

Laser induced incandescence determination of the ratio of the soot absorption functions at 532 nm and 1064 nm in the nucleation zone of a low pressure premixed sooting flame

In this work, the two-excitation wavelength laser induced incandescence (LII) method has been applied in a low-pressure premixed methane/oxygen/nitrogen flame (equivalence ratio 2.32) to determine the variation of the ratio of the soot absorption functions at 532 nm and 1064 nm E(m,532 nm)/E(m,1064 nm) along the flame. This method relies on the comparison of LII signals measured upon two different excitation wavelengths (here 532 nm and 1064 nm) and with laser fluences selected in such a way that the soot particles are equally laser-heated. The comparison of the laser fluences at 532 nm and 1064 nm leads to an easy determination of E(m,532 nm)/E(m,1064 nm). The reliability of the method is demonstrated for the first time in a low pressure flame in which the soot nucleation zone can be spatially resolved and which contains soot particles acting differently with the laser fluence according to their residence time in the flame. The method is then applied to determine the profile of E(m,532 nm)/E(m,1064 nm) along the flame. A very important decrease of this ratio is observed in the region of nascent soot, while the ratio remains constant at high distance above the burner. Implication on temperature determination from spectrally resolved measurement of flame emission is studied.     

水溶液中金属元素的激光诱导击穿光谱的检测分析

文章对竖直流动的CuSO₄和Pb(NO₃)₂水溶液样品表面的激光诱导击穿光谱的（简称LIBS）特性进行了观测分析。实验中采用的烧蚀激光波长为532 nm,脉冲宽度为10 ns,重复频率为10 Hz;LIBS信号的探测通过一色散相加型双光栅单色仪、Boxcar和PMT的组合来完成。通过对水溶液中金属元素的LIBS信号随时间和能量演化规律的分析,初步确定了系统 的最佳烧蚀能量和最佳探测延时。受样品表面附近空气击穿时氧元素信号的影响,实验对Cu和Pb各自的击穿位置进行了优化。在分析影响LIBS光谱探测因素的基础上,进一步优化了系统的工作条件和探测 参数。通过对不同浓度下LIBS信号的探测分析,初步确定了系统对Cu与Pb的最低检测浓度,分别约为31,50 ppm(μg·mL-1)。文章还对将LIBS技术运用到海水中重金属的实时在线检测的可 行性进行了讨论。     

Surface modifications of a titanium implant by a picosecond Nd:YAG laser operating at 1064 and 532 nm

Interaction of an Nd:YAG laser, operating at 1064 or 532 nm wavelength and pulse duration of 40 ps, with titanium implant was studied. Surface damage thresholds were estimated to 0.9 and 0.6 J/cm² at wavelengths 1064 and 532 nm, respectively. The titanium implant surface modification was studied by the laser beam of energy density of 4.0 and 23.8 J/cm² (at 1064 nm) and 13.6 J/cm² (at 532 nm). The energy absorbed from the Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following titanium/implant surface morphological changes were observed: (i) both laser wavelengths cause damage of the titanium in the central zone of the irradiated area, (ii) appearance of a hydrodynamic feature in the form of resolidified droplets of the material in the surrounding outer zone with the 1064 nm laser wavelength and (iii) appearance of wave-like microstructures with the 532 nm wavelength. Generally, both laser wavelengths and the corresponding laser energy densities can efficiently enhance the titanium/implant roughness. This implant roughness is expected to improve its bio-integration. The process of the laser interaction with titanium implant was accompanied by formation of plasma.     

Accumulation morphology on the surface of stainless steel irradiated by a nanosecond Nd:YAG pulsed laser

In this study, results in the irradiation of stainless steel AISI 304 in air with nanosecond laser pulses at laser irradiation power density 4×10⁷ W/cm² are reported. Laser processing parameters, such as wavelengths 532 and 1064 nm, pulse duration 20 ns and repetition rate 10 Hz were used. It is shown that the surface morphology of the stainless steel is related to the number of pulses applied to the same spot. The following surface morphological changes were observed: (i) occurrence of the micro-grains microstructures at wavelengths 532 and 1064 nm after 10 000 pulses irradiation and (ii) occurrence of vermiform-like microstructures at wavelength 1064 nm after 1000 pulses irradiation. Generally, it is concluded that irradiation due to several consecutive pulses caused significant damage and enhanced the stainless steel surface roughness.     

降雨对532nm和1064nm激光传输的衰减特性研究

降雨会对激光信号产生严重的衰减,从而给激光目标探测的应用带来一定影响.激光在降雨中的传输衰减已在红外波段做了大量的实验研究,而可见光波段激光在雨中的传输衰减特性还未见报道.基于夫琅禾费衍射和几何光学散射理论,建立雨滴对532 nm绿激光和1064 nm近红外激光光束的传输衰减模型,对比分析两波长激光在不同降雨量下的衰减...     

激光诱导击穿光谱检测水溶液中的Cr

利用激光诱导击穿光谱(LIBS)对溶液中的重金属元素Cr进行分析,开发一种快速、实时、在线的原位检测技术。采用1064nm的Nd∶YAG脉冲激光发生器作为光源,在相同的实验条件下,对配制的5种浓度的K2Cr2O7溶液进行击穿以产生等离子体,选取Cr的425.43nm线作为特征谱线,利用光谱仪自带的CCD探测器对谱线的LIBS信号进行收集,获得了5种浓度下Cr元素的光谱强度,建立了Cr元素谱线强度与其浓度拟合曲线。结果表明,溶液中Cr元素的浓度与其LIBS谱线强度有很好的线性关系,线性拟合决定系数达到0.9822。实验所得的结果为LIBS技术探测水质中的微量有毒金属元素提供了可行性,同时也为LIBS技术检测水质中金属元素含量提供了依据。     

Silver nanoparticles produced by PLD in vacuum: role of the laser wavelength used

In this work we report the results of investigation of silver (Ag) nanoparticles prepared on a silica substrate by laser ablation. Our attention was focused on the mean diameter, size distribution and optical absorption properties of nanoparticles prepared in vacuum by using different laser wavelengths. The fundamental wavelength and the second, third, and fourth harmonics of a nanosecond Nd:YAG laser were used for nanoparticles fabrication. The corresponding values of the laser fluence for each wavelength were: 0.6 J/cm² at 266 nm, 0.8 J/cm² at 355 nm, 2.8 J/cm² at 532 nm, and 2 J/cm² at 1064 nm. The Ag nanoparticles produced have mean diameters in the range from 2 nm to 12 nm as the nanoparticles’ size decreases with the decrease of the wavelength used. The presence of the Ag nanoparticles was also evidenced by the appearance of a strong optical absorption band in the measured UV-VIS spectra associated with surface plasmon resonance (SPR). A redshift and widening of the absorption peak were observed as the laser wavelength was increased. Some additional investigations were performed in order to clarify the structure of the Ag nanoparticles.     

Laser scribing of gallium doped zinc oxide thin films using picosecond laser

We report on a comprehensive study of picosecond laser scribing of gallium doped zinc oxide (GZO) thin films deposited on glass substrates using 355 nm, 532 nm and 1064 nm radiation, respectively. In this study, we investigated the influence of front side and rear side irradiation and determined single pulse ablation thresholds for all three wavelengths. Good ablation quality with full electrical isolation, steep groove walls and a smooth groove bottom was achieved by 355 nm rear side processing with a scanning speed of 224 mm/s. Ridges at the groove rims were found to be between 15 nm and 45 nm high. At similar scanning speed, laser scribing using 532 nm and 1064 nm radiation resulted in a lower ablation quality due to a higher roughness of the groove bottoms or higher ridges at the groove rims.     

Dual-wavelength investigation of laser-induced damage in multilayer mirrors at 532 and 1064 nm

Thin film beam splitters with high reflectivity at 532 nm and high transmittance at 1064 nm were deposited via reactive electron-beam evaporation with optimized parameters. The damage performance of the samples was investigated under irradiations of 532 nm laser only, 1064 nm laser only, and various combined laser fluences. The damages induced by the 1064 nm laser were primarily attributed to the initiators at the interface between the coatings and substrate. Under 532 nm laser irradiation only, two distinctive damage pits initiated by the submicron absorptive defects located at different coating depths and correlated to interfaces were observed. The damage effect under simultaneous irradiation in multilayer films was also investigated. The respective sensitive defects of the two lasers remained the precursors for causing damage. However, the dominant damage factors in simultaneous irradiation changed with the 1064 nm laser fluence, which also determined the coupling effect between the two lasers in terms of causing damage. Finally, correlative analysis methods were used to discuss the different coupling effects.     

Biocompatible film deposition by using Nd:YAG pulsed laser

A Nd:YAG laser operating at the fundamental wavelength (1064 nm) and at the second harmonic (532 nm), with 9 ns pulse duration, 100–900 mJ pulse energy, and 30 Hz repetition rate mode, was employed to ablate in vacuum (10^?6 mbar) biomaterial targets and to deposit thin films on substrate backings. Titanium target was ablated at the fundamental frequency and deposited on near-Si substrates. The ablation yield increases with the laser fluence and at 40 J/cm ² the ablation yield for titanium is 1.2×10¹⁶ atoms/pulse. Thin film of titanium was deposited on silicon substrates placed at different distance and angles with respect to the target and analysed with different surface techniques (optical microscopy, scanning electron spectrosopy (SEM), and surface profile).

Hydroxyapatite (HA) target was ablated to the second harmonic and thin films were deposited on Ti and Si substrates. The ablation yield at a laser fluence of 10 J/cm ² is about 5×10¹⁴ HA molecules/pulse. Thin film of HA, deposited on silicon substrates placed at different distance and angles with respect to the target, was analysed with different surface techniques (optical microscopy, SEM, and Raman spectroscopy).

Metallic films show high uniformity and absence of grains, whereas the bio-ceramic film shows a large grain size distribution. Both films found special application in the field of biomaterial coverage.