Microstructure evolution on the surface of stainless steel by Nd:YAG pulsed laser irradiation

New structure phenomena with the grain sizes of 60 nm to 1 μm would be expected on the stainless steel surface by Nd:YAG pulsed laser irradiation. Nano-structures with various shapes and sizes were formed mainly during the solidification and most shapes of particles were diversiform according to different distances from the center of the spot. The morphologies were of equiaxed nano-particles and faceted hexagons. The surface re-solidification velocities have been estimated according to the numeral simulation of the thermal conditions. It was proved by the XRD that they were mainly consisted of γ-Fe and manganese oxides. The XPS results confirmed the EDS results that on the surface the alloy elemental composition in the outermost layer were rich in Mn and poor in Fe and in reverse in the center of the laser spot. Through observation of morphologies grown on the laser irradiated surfaces, direct evidence of growth mode transition from a continuous form to a lateral form was provided in one laser spot.     

40mm孔径Nd:YAG片状器件的激光特性研究

本文首次报道了40mm孔径Nd:YAG片状激光器的激光特性.理论分析表明这类器件可望获得千瓦级激光平均功率.     

Characteristics of ultrafine tungsten particles produced by Nd:YAG laser irradiation

Ultrafine particles of tungsten were synthesized by the synchronized irradiation of a substrate in low He gas pressure with two pulsed Nd:YAG lasers. The primary particles have diameters of several nm as measured by transmission electron microscopy (TEM). An agglomeration of the primary particles was generated under high pressure and high laser power conditions. An electron diffraction analysis of the particles indicates that there exist two types of material structure: crystalline and amorphous-like. The size distribution was measured by a low-pressure differential mobility analyzer (LP-DMA). The peak of the size distribution was shifted from several nm to the tens of nm level with increasing pressure.     

Subhertz-linewidth Nd:YAG laser

Light from a Nd:YAG laser at 1064 nm is independently stabilized to two Fabry-Perot etalons situated on separate vibration-isolation platforms. A heterodyne beat measurement shows their relative frequency stability to be at the part-in-10(15) level at 5 s and the relative linewidth to be less than 1 Hz.     

Autonomous swinging of a lipid tubule under stationary irradiation by a Nd3+:YAG laser

A micrometer-sized lipid tubule exhibits oscillatory swinging motion under stationary irradiation by a Nd(3+):YAG laser ( lambda = 1064 nm). By choosing an appropriate optical path through an objective lens, the laser can be split into dual beams focused on the same position. Using this splitting, a lipid tubule can be shown to exhibit bistability with regard to the orientation of trapping. Driven by a temperature gradient induced by local photon heating, the trapped lipid tubule shows oscillatory motion between two possible orientations. This oscillatory phenomenon of the lipid tubule is thought to represent the breaking of time-translational symmetry under thermodynamically open conditions.     

Formation of nano-crystalline and amorphous phases on the surface of stainless steel by Nd:YAG pulsed laser irradiation

Thin surface layers consisting of nano-crystalline and amorphous phases on the surface of stainless steel have been attained under the Nd:YAG pulsed laser irradiation. The phases and microstructures were investigated by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM). The phase compositions of the surface determined by XRD were α-Fe (ferrite) and γ-Fe (austenite) or only γ-Fe in the near surface region on the bases of the different laser power densities. The nano-crystalline grains with sizes of 4-100 nm could result from high cooling rate and crystallization in amorphous region by homogeneous and heterogeneous nucleation. The formation of the amorphous phase was attributed to the higher cooling rates.     

Morphological and structural characterizations of different oxides formed on the stainless steel by Nd:YAG pulsed laser irradiation

The effects of laser surface irradiation on microstructure of AISI 304 stainless steel were investigated. The stainless steel surface was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). XRD patterns indicated that different oxides, such as chromium oxides and manganese oxides were fabricated successfully on the surface of the stainless steel by Nd:YAG pulsed laser irradiation. The effects of the growth conditions such as the laser power density on the morphologies of the different oxides have been investigated. From the FESEM, EDS (energy-dispersive spectrum) and TEM observations, the oxides with triangle-like, quadrangular and hexagonal morphologies have been fabricated successfully. The XPS was used to verify the formed oxides which had been detected by the XRD patterns. It was considered that laser power density had a critical role in the formation of different oxides.     

Crystalline patterning in Sm-doped sodium borate glass by CW Nd:YAG laser irradiation

Laser irradiation of glass materials has drawn much attention because this technique can offer a new processing method for spatially selected structural modification and/or crystallization in glass. Crystallized line and dot patterns at the micrometer scale were fabricated on the surface of Sm-doped sodium borate (Na₂O-B₂O₃) glass by irradiation of a continuous-wave Nd:YAG laser at λ = 1064 nm. The pattern sizes could be controlled by adjusting such parameters as scan rate, exposure time, and laser power. Analyses by Raman spectroscopy and X-ray diffraction revealed that the crystalline phase is Na₃Sm₂(BO₃)₃.     

Nd：YAG激光器中的自锁模

本文报道在Nd:YAG激光器中首次获得的自锁模脉冲序列.自锁模是由于Nd:YAG棒中的自相位调制引起的.在主被动对撞锁模运转情况下,自锁模对脉冲波形有较大的影响.     

高功率四波长Nd:YAG激光实验

四波长Nd：YAG激光实验是利用非线性晶体BBO，通过倍频、混频和二次倍频等激光变频技术，分别获取了4个波段相干辐射光，本文介绍了各波长相干辐射光的获取方法及其时空特性的测量。     

Dual-polarization mode-locked Nd:YAG laser

A mode-locked solid-state laser containing a birefringent element is shown to emit synchronously two frequency combs associated to the two polarization eigenstates of the cavity. An analytical model predicts the polarization evolution of the pulse train, which is determined by the adjustable intracavity birefringence. Experiments realized with a Nd:YAG laser passively mode locked by a semiconductor saturable absorber mirror are in perfect agreement with the model. Locking between the two combs arises for particular values of their frequency difference, e.g., half the repetition rate, and the pulse train polarization sequence is then governed by the relative overall phase offset of the two combs.     

Solar pumped Nd:YAG laser

We report the high efficiency of solar pumped laser. The sunlight is concentrated by the concentrator system, which is composed by the Fresnel lens and the cone-channel condenser. The power density of sunlight concentrated by the concentrator system surpasses the lasing threshold for pumping laser. In the experiment, the sunlight concentrated is coupled into the conical chamber pumping Nd:YAG laser media. Laser output of 3.5 W has been achieved; the collect efficiency is 3.5 W/m². The conversion efficiency is 1.0% from solar power into laser, and the slope efficiency is achieved 1.86%.     

Crown-like structure development on titanium exposed to multipulse Nd:YAG laser irradiation

We report micrometre-sized crown-like structure growth on a Ti surface by multipulse Nd:YAG (λ=1.064 μm,τ=170 ns) laser irradiation in air at atmospheric pressure. The irradiation was performed at 8×10⁷ W/cm² laser-pulse intensity, below the ablation threshold. A ring-shape structure develops in the centre of the irradiation spot after the action of five laser pulses. The further increase of the laser-pulse number leads gradually to a crown-like structure, which has, for 150 pulses, a height of 120–140 μm above the non-irradiated Ti surface. The forming crater’s depth does not exceed the height of the grown structure. In the neighbouring zone, after the action of 25 laser pulses, microcracks of the oxide surface layer develop. With the next pulses this leads to the formation of a surface microrelief. The crown-like-structure growth is originated by molten material movement attributed to the laser-induced plasma-recoil pressure. Received: 6 June 2001 / Accepted: 6 January 2002 / Published online: 26 March 2002     

Surface treatment of titanium by Nd:YAG laser irradiation in the presence of nitrogen

This work presents the surface treatment of commercial titanium alloy by means of a Nd:YAG (1.064 7m) laser in the presence of nitrogen. The treated surface was characterised by using scanning electron microscopy, atomic force microscopy, X-ray diffraction, secondary ion mass spectrometry, UV-visible spectrophotometry and microindentation. Experimental results show the formation of a nitrogen-rich layer, 500 nm thick, with a surface morphology characterised by the presence of polygonal structures which suggest that melting occurred under the action of the laser. The ' phase of titanium nitride was identified, in addition to a nitrogen in !-titanium solid solution. The reflectance spectrum of the yellow-golden sample is similar to that of deposited titanium nitride thin films. The hardness of the treated surface was measured by microindentation and found to be 14 GPa, a value three times higher than that of the titanium alloy. In scratch tests the nitrided layer detached at a load of 0.9 N.     

Effect of XeCl laser irradiation on the defect structure of Nd:YAG crystals

This paper presents the effect of XeCl laser irradiation on Nd:YAG single crystal samples with various number of pulses at different repetition rates and laser fluences. Effects of the irradiation on the optical and structural properties of the crystal are analyzed by UV–vis-NIR spectroscopy. Annihilation of some point defects of the crystal structure is observed following laser irradiation at a fluence of 100 mJ cm⁻² with 100 and 500 pulses. Increasing the laser fluence and pulse numbers leads to saturation and new defects are found to be formed in the crystal. Additional absorption spectra of the irradiated samples show that oxygen vacancies in the Nd:YAG crystals are removed during the low-dose irradiation. The laser irradiation is compared to the thermal annealing process for Nd:YAG crystal modification. Additional absorption spectrum of an annealed sample reveals that induced negative absorption band at 236 nm is correlated with the annihilation of the oxygen vacancy center. Our results also demonstrate that XeCl laser treatment has several advantages upon annealing at high temperatures in the Nd:YAG crystal quality improvement. Thus, the present work can give a new approach to modify Nd:YAG crystals to be used in a wide variety of solid-state laser engineering.     

The effects of pulsed Nd:YAG laser irradiation on surface energy of copper

The effect of laser surface treatment on the surface energy of copper plate was investigated in terms of the surface microstructure analysis and theoretical computation in this paper. The surfaces of the copper plates were treated by Nd:YAG pulsed laser with different powers. The microstructures of the treated copper plates were analyzed by optical microscopy and X-ray diffraction (XRD), and the wetting experiment was performed to evaluate the variation of surface energy. The results showed that the surface microstructure and the corresponding surface energy of copper, changed with the variation of the laser power. The experimental results further explained by XRD results and theoretical calculation, demonstrated that the surface energy changed when the crystal structure in the surface layer was re-oriented in a preferred orientation after laser irradiation.     

Analysis of laser drilled deep holes in stainless steel by superposed pulsed Nd:YAG laser radiation

Deep drilling of through holes in stainless steel (1.4301, sample thicknesses 5, 8 and 10 mm) has been performed with the superposed radiation of two pulsed Nd:YAG lasers with pulse duration of 0.5 ms superposed by 17 ns pulses. The drilling efficiency is improved by the spatially and temporally superposed radiation of the two lasers. The enhanced drilling speed and the larger reproducibility of the drilling time are explained by a modified formation of closures in the hole during percussion drilling which are recorded by high-speed photography. The metallographic hole analysis exhibits high-temperature oxidation marks. The development of these marks is described by a ray tracing of the incident beam within the hole and the resulting intensity distribution at the hole wall.     

Damage on HfO2/SiO2 high-reflecting coatings under single and multiple Nd:YAG laser pulse irradiation

The single- and multi-shot damage behaviors of HfO2/SiO2 high-reflecting (HR) coatings under Nd:YAG laser exposure were investigated. Fundamental aspects of multi-shot laser damage, such as the instability due to pulse-to-pulse accumulation of absorption defect and structural defect effect, and the mechanism of laser induced defect generation, are considered. It was found in multi-shot damage, the main factors influencing laser-induced damage threshold (LIDT) are accumulation of irreversible changes of structural defects and thermal stress that induced by thermal density fluctuations.     

Frequency-tripled Nd:YAG laser ablation in laser structuring process

With the increasing demand for finer lines/spaces on PCB boards, a new technology—laser structuring—has emerged in recent years. In this research, the frequency-tripled Nd:YAG laser is selected as the laser source in laser structuring; this laser is often used in miniaturization machining. This paper describes in detail the processing parameters’ influences, such as laser power, numbers of repetition, repetition rate and bite size, on laser structuring results. From the research results, it can be concluded that the line width and depth are increased with increases in the laser power and numbers of repetition. Repetition rate, bite size and velocity are related to one another. When the bite size is fixed, the velocity increases with the repetition rate and the depth of the line is decreased at the same time. When the repetition rate is fixed, velocity increases with the bite size.     

大功率Nd∶YAG固体激光器

介绍了一台单级输出灯泵浦大功率脉冲Nd∶YAG激光器。该激光器脉宽0.1-10ms可调,频率1-1000hz可调,总注入电功率12kw。试验得到激光器参数脉冲宽度和频率协调改变,可使激光器在整个脉宽范围内都能稳定500w输出;最大单脉冲能量56J;总体电光效率4.2%;光束质量为25mm.mrad;功率稳定性±2%。