Laser removal of copper particles from silicon wafers using UV, visible and IR radiation

Laser removal of small copper particles from silicon wafer surfaces was carried out using Nd:YAG laser radiation from near-infrared (1064 nm) through visible (532 nm) to ultraviolet (266 nm). It has been found that both 266 nm and 532 nm are successful in removing the particles from the surface whereas 1064 nm was shown to be ineffective in the removal of particles. The damage-threshold laser fluence at 266 nm was much higher than other wavelengths which provides a much wider regime for safe cleaning of the surface without causing any substrate damage. The cleaning efficiency was increased with a shorter wavelength. The effect of laser wavelength in the removal process is discussed by considering the adhesion force of the particle on the surface and the laser-induced cleaning forces for the three wavelengths. Received: 31 May 2000 / Accepted: 14 July 2000 / Published online: 20 June 2001     

Intracavity optical parametric oscillator at 1572-nm wavelength pumped by passively Q-switched diode-pumped Nd:YAG laser

An intracavity optical parametric oscillator (IOPO) based on bulk KTP crystal was constructed with a Nd:YAG slab as an active medium pumped by a 300-W diode array and Cr:YAG as a passive Q-switch. A signal pulse of 1.9-mJ energy at 1572-nm wavelength was demonstrated. In the cavity, optimized with respect to single-pulse energy, a five-fold shortening of signal-pulse duration with respect to 1064-nm pump radiation was observed. A twice as large level of signal peak power of 650 kW, compared to the pump laser in the same cavity without the IOPO, was achieved. A conversion efficiency of 44% with respect to the 1064-nm pump beam and 3.8% with respect to diode pump energy was demonstrated. Received: 15 October 2002 / Revised version: 19 February 2003 / Published online: 16 April 2003 RID="*" ID="*"Corresponding author. Fax: +48-22/666-8950, E-mail: wzendzian@wat.edu.pl     

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     

1064 nm和532 nm纳秒激光同时辐照熔石英损伤规律的研究

利用Nd: YAG激光器研究基频(1064 nm)与倍频(532 nm)单独辐照和同时辐照下熔石英的损伤规律,对损伤几率进行了测试,获得损伤几率曲线与典型损伤形貌。研究结果表明:双波长同时辐照下的初始损伤阈值总是小于单波长辐照下的初始损伤阈值;基频光中加入定量倍频光后,熔石英对基频光的吸收效率提高;并且双波长同时辐照下,熔石英损伤密度增大;原因主要是熔石英表面缺陷对不同波长吸收机制的差异。     

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.     

Characterization of laser-ablated and chemically reduced silver colloids in aqueous solution by UV/VIS spectroscopy and STM/SEM microscopy

Silver colloids in aqueous solution were studied by different scanning microscopy techniques and UV/VIS spectroscopy. The silver colloids were produced either by chemical reduction or by nanosecond laser ablation from a solid silver foil in water. Variation of laser power and ablation time leads to solutions of metal clusters of different sizes in water. We characterized the electronic absorption of the clusters by UV/VIS spectroscopy. STM (scanning tunneling microscope) imaging of the metal colloids shows atomic resolution of rod- or tenon-like silver clusters up to 10-nm length formed by laser ablation. Our scanning electron microscope measurements, however, show that much larger silver colloids up to 5-μm length are also formed, which are not visible in the STM due to their roughness. We correlate them with the long-wavelength tail of the multimodal UV/VIS spectrum. The silver colloids obtained by chemical reduction are generally larger and their electronic spectra are red-shifted compared to the laser-ablated clusters. Irradiation of the colloid solution with nanosecond laser pulses of appropriate fluence at 532 nm and 355 nm initially reduced the colloid size. Longer irradiation at 355 nm, however, leads to the formation of larger colloids again. There seems to be a critical lower particle size, where silver clusters in aqueous solution become unstable and start to coagulate. Received: 24 June 2002 / Revised version: 25 July 2002 / Published online: 25 October 2002 RID="*" ID="*"This work is part of the thesis of H. M?ltgen RID="**" ID="**"Corresponding author. Fax: +49-211/811-5195, E-mail: kleinermanns@uni-duesseldorf.de     

Target-plane deposition of diamond-like carbon in pulsed laser ablation of graphite

In pulsed Nd:YAG laser ablation of highly oriented pyrolytic graphite (HOPG) at 10⁻⁶ Torr, diamond-like carbon (DLC) are deposited at laser wavelengths of 1064, 532, and 355 nm on substrates placed in the target-plane. These target-plane samples are found to contain varying sp³ content and composed of nanostructures of 40-200 nm in size depending on the laser wavelength and laser fluence. The material and origin of sp³ in the target-plane samples is closely correlated to that in the laser-modified HOPG surface layer, and hardly from the backward deposition of ablated carbon plume. The surface morphology of the target-plane samples shows the columnar growth and with a tendency for agglomeration between nanograins, in particular for long laser wavelength at 1064 nm. It is also proposed that DLC formation mechanism at the laser-ablated HOPG is possibly via the laser-induced subsurface melting and resolidification.     

Analysis of laser micro drilled holes through aluminium for micro-manufacturing applications

Conventional laser machining of aluminium with long wavelength lasers has its inherent problems due to the high reflectivity of aluminium to laser radiation (Handbook of Optics, vol 1, 2nd ed. New York: McGraw-Hill; 1995). Laser processing at shorter wavelengths reduces the reflectivity of the workpiece to the incident laser radiation and can also reduce the dimensions of the obtainable machining geometries. This paper reviews the limiting factors in the micro machining of aluminium using a diode pumped solid state (DPSS) Nd:YAG laser operated at 1064, 532, and 355 nm. The geometries of the laser-machined samples were investigated using interferometric, and optical methods to assess how the processing fluence and wavelength will affect the obtainable precision for successful integration of the laser in a micromachining CAD/CAM system.     

LD泵浦355nm准连续紫外激光器

报道了一台LD侧面泵浦Nd:YAG晶体的内腔三次谐波转换的全固态准连续紫外激光器。在谐振腔内,1064nm的基频波通过对Ⅱ类相位匹配KTP晶体进行二倍频来产生532nm波长激光,二者再通过对Ⅱ类相位匹配LBO晶体进行和频来获得355nm紫外激光输出。355nm全固态紫外激光器在声光调Q重复频率为2.8kHz下,当输入电流为18A时可得到503mW的激光输出。     

基于Nd∶YAG/Cr∶YAG复合晶体的全固态紫外激光器

被动调Q产生1064 nm脉冲激光在腔外聚焦后入射到KTP中,产生532 nm的倍频光,再通过LBO和频产生355 nm激光。当抽运功率为3.4 W时,基频光调Q输出平均功率为350 mW,峰值功率达3.5 kW。腔外二倍频532 nm绿光输出平均功率为110 mW,用Ⅰ类相位匹配LBO晶体和频获得36 mW的355 nm的紫外激光输出,三倍频效率(1064~355 nm)达到10.2%。由于Cr∶YAG晶体达到饱和吸收后,会呈现出各向异性的特征,对基频光的偏振状态有很大影响。实验中必须合理放置复合晶体,使基频光的偏振状态为近似线偏振以提高转换效率。     

铅原子非共振多光子电离过程的研究

在激光波长为1064nm、532nm和355nm下,研究了铅原子的非共振多光子过程.通过改变激光脉冲的线宽研究了铅原子非共振7-光子电离速率和激光统计性的依赖关系.     

Laser-assisted decontamination—A wavelength dependent study

We present here the experimental results on cleaning of radioactive dielectric particulates, loosely deposited on stainless steel, by coherent light of 1064 nm wavelength and its three harmonics occurring at 532 nm, 355 nm and 266 nm, derived from an Nd-YAG laser. For the initial few exposures, the decontamination factor has been found to be highest when exposed to 1064 nm radiation. With increasing number of exposures, however, the radiation with reducing wavelength assumes a more important role as a cleaning agent. The observation of almost no cleaning with 1064 nm and much reduced cleaning with its harmonics when the contamination is deposited on a transparent substrate confirms the dominant role played by metal substrate towards expelling the loose particulates from its surface.     

Photoluminescence of ZnO nanoparticles generated by laser ablation in deionized water

Zinc oxide (ZnO) nanoparticles were synthesized using pulsed laser ablation of a Zn metal plate in deionized water without using surfactant. The beam of a Q-switched Nd:YAG laser of 1064-nm and 532-nm wavelengths at 6-ns pulse width and different fluences is employed to irradiate the solid target in water. Transmission electron microscopy images revealed that the size of the ZnO nanoparticles formed by the 532-nm wavelength laser beam is smaller than that of the nanoparticles generated by the 1064-nm wavelength laser beam. The room-temperature photoluminescence spectra of the ZnO nanoparticles show intense violet emission along with emission in blue and green bands. The excellent ultraviolet emission indicates that the ZnO nanostructures have a low defect concentration.     

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.     

Generation of CdS clusters using laser ablation: the role of wavelength and fluence

The formation of cationic clusters in the laser ablation of CdS targets has been investigated as a function of wavelength and fluence by mass spectrometric analysis of the plume. Ablation was carried out at the laser wavelengths of 1064, 532, 355, and 266 nm in order to scan the interaction regimes below and above the energy band gap of the material. In all cases, the mass spectra showed stoichiometric Cd _n S _n ⁺ and nonstoichiometric Cd _n S _n−1⁺, Cd _n S _n+1⁺, and Cd _n S _n+2⁺ clusters up to 4900 amu. Cluster size distributions were well represented by a log-normal function, although larger relative abundance for clusters with n=13, 16, 19, 34 was observed (magic numbers). The laser threshold fluence for cluster observation was strongly dependent on wavelength, ranging from around 16 mJ/cm² at 266 nm to more than 300 mJ/cm² at 532 and 1064 nm. According to the behavior of the detected species as a function of fluence, two distinct families were identified: the “light” family containing S₂⁺ and Cd⁺ and the “heavy” clusterized family grouping Cd₂⁺ and Cd _n S _m ⁺. In terms of fluence, it has been determined that the best ratio for clusterization is achieved close to the threshold of appearance of clusters at all wavelengths. At 1064, 532, and 355 nm, the production of “heavy” cations as a function of fluence showed a maximum, indicating the participation of competitive effects, whereas saturation is observed at 266 nm. In terms of relative production, the contribution of the “heavy” family to the total cation signal was significantly lower for 266 nm than for the longer wavelengths. Irradiation at 355 nm in the fluence region of 200 mJ/cm² has been identified as the optimum for the generation of large clusters in CdS.     

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.     

A four-wavelength depolarization backscattering LIDAR for polar stratospheric cloud monitoring

A four wavelength backscattering depolarization LIDAR designed for polar stratospheric cloud and stratospheric aerosol measurement is described. The system uses the following wavelengths: 355 nm, 532 nm, 750 nm, and 850 nm. These wavelengths, obtained by means of the third- and second-harmonic of a Nd: YAG laser and by means of a tunable Ti: Sapphire laser, are chosen in a way to better characterize the particel size of such stratospheric aerosols. They are not emitted simultaneously as the LIDAR system is designed with only two detection channels permitting to detect, in the analog and in the photon counting mode, both the direct and the depolarized backscattered signal. The system has been operational in northern Finland since the end of November 1991.     

Synchronously pumped femtosecond optical parametric oscillator of congruent and stoichiometric MgO-doped periodically poled lithium niobate

A synchronously pumped femtosecond optical parametric oscillator based on congruent MgO-doped periodically poled lithium niobate (c-MgO:PPLN) is reported. The system, operating at room temperature, was pumped by a mode-locked Ti:sapphire laser. The wavelengths of the signal and idler waves were tuned from 870 nm to 1.54 μm and 1.58 to 5.67 μm, respectively, by changing the pump wavelength, the grating period or the cavity length. Pumped by 1.1 W of 755 nm laser radiation, the OPO generated 310 mW of 1080 nm radiation. This signal output corresponds to a total conversion efficiency of 50%. Without dispersion compensation the OPO generated phase-modulated signal pulses of 200 fs duration. Besides the OPO of c-MgO:PPLN, an OPO of stoichiometric (s) MgO:PPLN was investigated. Because of the reduced sensitivity to photorefractive damage, both crystals allowed efficient OPO operation at room temperature. Received: 19 August 2002 / Revised version: 11 December 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-631/205-3906, E-mail: andres@physik.uni-kl.de     

A compact frequency-doubled 10-kHz PRF copper-vapour-laser-pumped dye laser

A 10-kHz pulse-repetition-frequency dye-laser master-oscillator power amplifier, end-pumped by a copper vapour laser (CVL), is reported. This laser was based on recently available, lightweight and compact CVL and dye laser components. Dye laser tunability was achieved from 592 to 622 nm and, when the oscillator was etalon line-narrowed, up to 1.5 W of single-etalon-mode output was obtained from the amplifier at the 608-nm peak tuning wavelength. By frequency doubling this amplified output in a BBO crystal we obtained up to 225 mW of 5-GHz 308-nm output, which is suitable for the performance of tropospheric hydroxyl radical concentration measurements. Received: 16 July 2002 / Revised version: 6 November 2002 / Published online: 5 February 2003 RID="*" ID="*"Present address: Department of Geography, University of Cambridge, Cambridge, CB2 3EN, UK RID="**" ID="**"Corresponding author. Fax: +44-1865/272400, E-mail: d.coutts1@physics.ox.ac.uk     

The effect of laser wavelength on the ablation rate of carbon

The ablation of graphite is studied as a function of laser fluence for 355, 532 and 1,064 nm wavelength generated by a nanosecond Nd:YAG laser. It has been found that in the case of lower wavelengths, the transition from the thermal ablation to the phase explosion takes place at lower laser fluences. The change of crater shape due to the effect of deep drilling in the proximity of the phase explosion threshold was observed. The calculations of plasma radiation flux to the target surface were made, and the considerable increase of absorbed energy density was found in the case of 355 nm wavelength.