The influence of pulse duration on the stress levels in ablation of ceramics: A finite element study

We present a finite element model to investigate the dynamic thermal and mechanical response of ceramic materials to pulsed infrared radiation. The model was applied to the specific problem of determining the influence of the pulse duration on the stress levels reached in human dental enamel irradiated by a CO₂ laser at 10.6 μm with pulse durations between 0.1 and 100 μs and sub-ablative fluence. Our results indicate that short pulses with durations much larger than the characteristic acoustic relaxation time of the material can still cause high stress transients at the irradiated site, and indicate that pulse durations of the order of 10 μs may be more adequate both for enamel surface modification and for ablation than pulse durations up to 1 μs. The model presented here can easily be modified to investigate the dynamic response of ceramic materials to mid-infrared radiation and help determine optimal pulse durations for specific procedures.     

Laser ablation lithography on thermoelectric semiconductor

In this paper, experimental results of the investigation of the periodic structure on thermoelectric semiconductor Cu₂Se are presented. Periodic structures were formed on surfaces of semiconductors due to multi-beam interaction of Q-switched Nd:YAG laser, which was operated in the lowest order of Gaussian mode and pulse duration 7 ns. Surface temperature evolution and transient reflectivity are studied during laser treatment. Creation of Cu islands in the maximal intensity of interference pattern was found.     

Matrix assisted pulsed laser evaporation processing of triacetate-pullulan polysaccharide thin films for drug delivery systems

We report the first successful deposition of triacetate-pullulan polysaccharide thin films by matrix assisted pulsed laser evaporation. We used a KrF* excimer laser source (λ = 248 nm, τ ≈ 20 ns) operated at a repetition rate of 10 Hz. We demonstrated by FTIR that our thin films are composed of triacetate-pullulan maintaining its chemical structure and functionality. The dependence on incident laser fluence of the induced surface morphology is analysed.     

Quantum states in fabricating poly-Si films

The quantum states are presented in these processions of fabricating poly-Si films. Amorphous silicon films prepared by PECVD has been crystallized by conventional furnace annealing (FA) and rapid thermal annealing (RTA), respectively. It is found that the thin films grain size present quantum states with the increasing of the gas flow ratios of SiH₄, H₂ mixture, substrate temperatures, frequency power, annealing temperature and time.     

Measurements of NH3 in the ν2 = 1 state by a solid-state, photomixing, THz spectrometer, and a simultaneous analysis of the microwave, terahertz, and infrared transitions between the ground and ν2 inversion-rotation levels

In this paper, we report 30 THz measurements of ammonia in its excited, ν₂ = 1, inversion state. These measurements include transition frequencies and pressure shifts (where significant enough to be observed). Included in the data are two forbidden and three ro-inversion transitions, as well as 18 transitions never directly measured before. The measurements were made with an all-solid-state, diode-laser, difference-frequency spectrometer. Using an innovative laser-frequency locking scheme, this spectrometer provided accurately determined and continuously tuned THz-frequencies without requiring accurate knowledge of the absolute laser frequencies. The details of the spectrometer’s frequency calibration is discussed. A global analysis of NH₃ based on the available ground state, ν₂ = 1 state, and ν₂-band transitions was carried out, and the resulting set of recommended molecular effective-Hamiltonian parameters for ammonia is presented. In addition, calculated center frequencies and intensities for all possible transitions up to J = 20 between rotation, inversion, and vibration levels in the ground and ν₂ = 1 states are included as supplementary material.     

液相基质中重金属元素激光诱导击穿光谱实验参数的优化

针对混合溶液中重金属元素的激光诱导击穿光谱(LIBS)测量系统,为提高测量系统的检测灵敏度,以提高混合溶液中Ca和Cr金属元素LIBS光谱线强度的信噪比为目标,对LIBS测量系统中的激光脉冲能量、液相样品流速、ICCD门宽、延时等实验参数进行了优化,得到最优化参数激光脉冲能量、样品流速、ICCD门宽、延时分别为35 m J、30 ml/min、1400 ns和2400 ns,为降低LIBS技术应用于混合溶液中痕量重金属元素的检出限提供了实验参数支撑.     

高温氧气热处理对TiO_2晶体结构和铁磁性的影响

金红石TiO_2晶体先在真空中进行退火处理,随后在1173 K的氧气中进行不同时间(2 h、5 h、8 h)的热处理.理论上,通过Doppler程序计算了晶体中存在单空位、双空位和间隙O原子时的正电子湮没寿命.实验上,利用正电子湮没寿命谱仪、符合多普勒能谱仪和超导量子干涉仪分别表征了氧气退火后晶体内部的缺陷结构和常温铁磁性.分析结果得出:真空退火晶体的常温铁磁性主要与O空位的存在相关联;而经过氧气退火后,虽然极大地减少了氧空位,但晶体中却产生了大量的Ti双空位,这使得晶体的常温铁磁性有所增加.     

真空退火对L1_0-CoPt薄膜结构、磁性及表面形貌的影响

本文利用磁控溅射的方法制备了L1_0-CoPt薄膜,研究了不同退火条件对薄膜结构、磁性以及表面形貌的影响.通过优化退火温度、保温时间以及升温速率,制备出了具有大矫顽力、高矩形比、粗糙度小的垂直各向异性L1_0-CoPt薄膜.实验发现,较高的退火温度有利于克服CoPt薄膜有序化转变所需要的能量,同时适当延长退火时间可以提高CoPt薄膜的扩散系数,从而促使无序相fcc转化为L1_0有序相fct结构.此外,退火过程中减缓升温速率可以有效减小薄膜粗糙度,从而形成平整连续膜.     

模拟退火遗传算法在多声源定位中的应用

利用声源定位技术测量弹丸落点坐标时,针对多发炮弹短间隔连续射击试验中,传感器接收信号的时序关系复杂,严重影响声源定位结果准确性的问题,提出了采用模拟退火遗传算法实现短间隔连续多声源目标的精确定位。试验测试了发射间隔为0.15 s的7发炮弹在600 m×600 m区域内的定位情况,结果表明:文章的算法能快速有效的对短间隔连续多声源目标进行定位解算,定位精度小于5 m。     

Ion implantation induced by Cu ablation at high laser fluence

High energy laser plasma-produced Cu ions have been implanted in silicon substrates placed at different distances and angles with respect to the normal to the surface of the ablated target. The implanted samples have been produced using the iodine high power Prague Asterix Laser System (PALS) using 438 nm wavelength irradiating in vacuum a Cu target. The high laser pulse energy (up to 230 J) and the short pulse duration (400 ps) produced a non-equilibrium plasma expanding mainly along the normal to the Cu target surface. Time-of-flight (TOF) technique was employed, through an electrostatic ion energy analyzer (IEA) placed along the target normal, in order to measure the ion energy, the ion charge state, the energy distribution and the charge state distribution. Ions had a Boltzmann energy distributions with an energy increasing with the charge state. At a laser fluence of the order of 6 × 10⁶ J/cm², the maximum ion energy was about 600 keV and the maximum charge state was about 27+.In order to investigate the implantation processes, Cu depth profiles have been performed with Rutherford backscattering spectrometry (RBS) of 1.5 MeV helium ions, Auger electron spectroscopy (AES) with 3 keV electron beam and 1 keV Ar sputtering ions in combination with scanning electron microscopy (SEM). Surface analysis results indicate that Cu ions are implanted within the first surface layers and that the ion penetration ranges are in agreement with the ion energy measured with IEA analysis.