Study of Nanocrystalline Diamond Film Deposited Rapidly by 500 W Excimer Laser

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脉冲光纤激光修锐青铜金刚石砂轮等离子体特性研究

采用光栅光谱仪 对脉冲光纤激光修锐青铜金刚石砂轮过程中产生的等离子体空间分辨发射光谱进行了测量. 研究了500–600 nm波段范围内的等离子体空间发射光谱强度随激光平均功率和脉冲重复频率的变化情况. 结果表明: 等离子体辐射光谱强度在其径向膨胀方向上距离砂轮表面约2.4 mm处达到最大值. 在局部热力学平衡假设条件下, 根据等离子体中六条铜原子谱线的相对强度, 利用Boltzmann 图法, 计算得到在不同激光功率和重复频 率条件下的等离子体电子温度沿砂轮径向方向的分布规律. 实验结果表明: 在激光修锐青铜金刚石砂轮过程中, 距离砂轮表面约3 mm处等离子体电子温度出现峰值, 其温度最高可达4380 K, 且等离子体电子温度随着激光参数和 空间位置的改变呈现出不同的演变规律. 关键词： 脉冲光纤激光 等离子体发射光谱 激光修锐 电子温度     

A study of a Q-switched double-clad ytterbium-doped fiber laser with amplifying effect

A high repetition rate ytterbium-doped double-clad (YDDC) fiber laser with amplifying effect is described by using acousto-optic modulator. The characteristic of Q-switched pulses are studied with accurate control of opening gate time of modulator. The stable Q-switched pulses with tens of nanoseconds width can be observed at high repetition rate varied from 50 kHz to 500 kHz using this laser. The stable operation area of the Q-switched fiber laser is discussed and the analysis results agree well with that of the experiment.     

High repetition rate laser ablation for vapor–liquid–solid nanowire growth

A high repetition rate (500 kHz) solid state laser was used for the ablation process in a Pulsed Laser Deposition (PLD)/Vapor–Liquid–Solid (VLS) growing. A ZnO target was ablated with laser powers between 0.6 W and 1.2 W, and a variable number of pulses per train and trains frequencies. ZnO structures were grown on gold patterned and unpatterned substrates surfaces. Enhanced growth of the nanostructures could be noticed on the catalyst patterned surfaces. Better nanowire morphologies were also observed for bigger number of laser pulses per train. The enhancements are more evident for low laser powers. Based on plume expansion investigations, by using a high speed camera and a Particle-In-Cell (PIC) Monte-Carlo based simulations, the nanostructure morphology variations could be understood on the basis of the plume particles diffusion process and thin film versus VLS growing competition.     

PLD方法制备的超硬非晶碳薄膜研究

 用脉冲激光沉积在不同条件下制备非晶碳超硬薄膜，研究了非晶碳超硬薄膜的表面形貌、结构、应力、硬度以及能谱等。原子力显微镜和扫描电镜图像显示，薄膜表面平整、致密且光滑,均方根粗糙度最大为0.877 nm。在高激光重复频率、高激光通量条件下，薄膜有很大的应力，致使膜层褶皱甚至破裂，小角X射线衍射表明薄膜为非晶态且最大残余应力达30 GPa以上,但300 ℃温度的原位退火可以有效降低残余应力；纳米压痕测试表明薄膜硬度大于20 GPa，弹性模量大于200 GPa；X射线光电子能谱表明薄膜中sp3的含量在39%~53%之间变化，并且与激光通量成正比。     

新型结构声光调Q激光器研究

为了提高声光调Q输出脉冲的重复率;通过分析影响脉冲输出特性的因素,提出了采用新颖的掠入射方式、线泵浦源侧面泵浦的特殊谐振腔结构,在泵浦功率50 W时,实现了重复频率500 kHz、脉冲宽度76.82 ns的高重复频率激光脉冲输出.结果表明,缩短脉冲建立时间,提高泵浦功率,可以有效地提高声光调Q激光器的重复频率.     

Ultrafast three-dimensional submicrometer-resolution readout of coherent optical-phonon oscillations with shaped unamplified laser pulses at 20 MHz

An ultrafast three-dimensional readout of coherent optical-phonon oscillations from a diamond film is demonstrated using temporally and spectrally shaped ultrashort laser pulses, delivered by a compact, oscillator-only laser system. This system integrates a long-cavity ytterbium-fiber-laser-pumped 30?fs Cr:forsterite oscillator with a photonic-crystal-fiber soliton frequency shifter and a periodically poled lithium niobate spectrum compressor, providing coherent Raman excitation and time-delayed interrogation of optical phonons in diamond at a 20?MHz repetition rate with a submicrometer spatial resolution.     

Film growth and mechanism of LICVD of chromium films from Cr(CO)6 at 248 nm

The probe-beam transmission method was used to study the chemical vapor deposition of chromium films due to photodecomposition of Cr(CO)₆ by pulsed excimer laser radiation at 248 nm in a reversed-substrate configuration, where the film forms on the quartz entrance window of the deposition cell. The dependence of the deposition rate and the film formation time on the laser pulse intensity and repetition rate as well as on the Ar buffer gas pressure was determined for different stages of the deposition process. The experiments were performed at room temperature, on a deposition area of about 0.15 cm², with laser fluences up to 100mJ cm^–2, pulse repetition rates between 5 and 80 pps and buffer gas pressures between 10 and 700 mbar. The results are discussed within the framework of a simple model for LICVD. They reveal the dominant role of gas-phase photodissociation and diffusion in chromium film deposition under the conditions employed. Some results concerning the morphology and the depth distribution of Cr, O, and C in films deposited in the reversed-substrate configuration are also presented.     

光溅射镀膜均匀性的优化模拟

为了改善脉冲激光溅射沉积大面积薄膜的均匀性,发展了基片离轴旋转的扫描技术.根据基片离轴旋转的基本原理和等离子体羽空间余弦分布规律,建立了径向膜厚分布公式.数值模拟了各种因素对基片离轴旋转扫描沉积薄膜均匀性的影响.分析表明,优化粒子束中心与基片中心偏置距离、溅射点与基片的距离是改善基片离轴旋转扫描镀膜均匀性的主要途径.同时也考虑了电机转速、镀膜时间和激光重频的影响.通过参量优化,当均匀度要求在95％时,计算得到薄膜的最大半径超过40 mm.     

金刚石窗口冷却Yb3+∶YAG DPSSL设计

针对高功率二极管重复率抽运的V型非稳腔Yb3+∶YAG激光头，提出了利用金刚石窗口冷却和直接水冷相结合的复合冷却设计.在YAG片的抽运面进行直接水冷，同时在激光提取面利用金刚石窗口冷却介质.金刚石优异的导热性能不仅能够有效地冷却激光介质，还能消除横向的温度梯度，解决了高功率激光器冷却和高功率抽运的矛盾.模拟结果表明对掺杂10 at %厚度为1.6 mm的Yb3+∶YAG片在抽运功率密度为20 kW/cm2，重复频率为10 Hz的条件下，要将最高温度控制在可接受的范围内（比如320 K），周围冷却水的对流换热系数约为4000 W/m2K.     

脉冲激光气相沉积法制备钴纳米薄膜实验研究

 采用脉冲激光沉积技术制备了钴纳米薄膜，分析和讨论了不同背景气压和脉冲频率对钴纳米薄膜表面形貌的影响及纳米微粒的形成机理。实验结果表明：在低背景气压下，等离子体羽辉自身粒子之间的碰撞占主导作用，容易形成液滴；在较高背景气压下，等离子体羽辉边缘粒子和背景气体粒子之间的碰撞占主导作用，容易形成小岛并凝聚成微颗粒；在4Hz的脉冲重复频率和5Pa背景气压下生长出单分散性良好的钴纳米颗粒。     

Multilayer growth of BaTiO3 thin films via pulsed laser deposition: An energy-dependent kinetic Monte Carlo simulation

An energy-dependent kinetic Monte Carlo approach was proposed to simulate the multilayer growth of BaTiO₃ thin films via pulsed laser deposition, in which the four steps, such as the deposition of atoms, the diffusion of adatoms, the bonding of adatoms, and the surface migration of adatoms, were considered. Distinguishing with the traditional solid-on-solid (SOS) model, the adatom bonding and the overhanging of atoms, according to the perovskite structure, were specially adopted to describe the ferroelectric thin film growth. The activation energy was considered from the interactions between the ions, which were calculated by Born-Mayer-Huggins (BMH) potential. From the simulation the relative curves of the each layer coverage and roughness vs total coverage were obtained by varying the parameter values of the incident kinetic energy, laser repetition rate and mean deposition rate. The relationship between growth modes and the different parameters was also acquired.     

基于少数层石墨烯可饱和吸收的锁模光纤激光器

本文利用化学气相沉积法高温分解甲烷在铜箔上制得单层石墨烯薄膜, 测量了石墨烯的拉曼光谱. 将石墨烯薄膜逐层转移到光纤跳线的氧化锆插芯端面上做成可饱和吸收材料, 实验研究了环形腔掺铒光纤脉冲激光器的输出特性, 获得了峰值波长为1560.1 nm, 3 dB带宽为0.27 nm, 重复频率为7.69 MHz, 脉冲宽度为58.8 ps 的锁模脉冲序列. 时间带宽积为1.98, 表明脉冲出现了啁啾. 最后, 通过改变两个光纤活动接头之间的空气腔的长度, 激光波长实现了4 nm的调谐. 关键词： 光纤激光器 石墨烯 锁模     

High-peak-power optically pumped AlGaInAs eye-safe laser at 500-kHz repetition rate with an intracavity diamond heat spreader

We report on a compact efficient high-repetition-rate (>100?kHz) optically pumped AlGaInAs nanosecond eye-safe laser at 1525?nm. A?diamond heat spreader bonded to the gain chip is employed to improve the heat removal. At a pump power of 13.3?W, the average output power at a repetition rate 200?kHz is up to 3.12?W, corresponding to a peak output power of 560?W. At a repetition rate 500?kHz, the maximum average power and peak power are found to be 2.32?W and 170?W, respectively.     

Wear resistance of ZrC/TiN and ZrC/ZrN thin multilayers grown by pulsed laser deposition

ZrC/TiN and ZrC/ZrN multilayers thinner than 350 nm were grown on (100) Si substrates at a temperature of 300 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser (λ=248 nm, pulse duration τ=25 ns, 8.0 J/cm² fluence and 40 Hz repetition rate). Cross-sectional transmission electron microscopy, Auger electron spectroscopy depth profiling and simulations of X-ray reflectivity curves indicated that there was intermixing between the deposited layers at the interfaces as well as between the first layer and the substrate. Nanoindentation investigations found hardness values between 35 and 38 GPa for the deposited multilayers. Linear unidirectional sliding wear tests were conducted using a ball-on-plate tribometer under 1 N normal force. Wear tracks were produced in a Hysitron nanoindenter with 1 μm radius diamond tip under a 500 μN load. High-resolution cross-sectional transmission electron microscopy studies of the wear tracks showed that the multilayers withstood these tests without significant damage. The results could be explained by the use of a high laser fluence during deposition that resulted in very dense and strongly adherent nanocrystalline layers.     

基于人造金刚石晶体的拉曼激光器研究进展

受激拉曼散射是一种重要的非线性光学频率变换技术,在拓展激光波段方面有十分广泛的应用前景。因此,寻找具有优良光学性质的拉曼介质,提高拉曼激光器性能,具有重要的研究价值。相比于传统的固体拉曼晶体,人造金刚石晶体具有拉曼增益系数大、拉曼频移大、导热率高和透过性好等显著优点,基于人造金刚石晶体的拉曼激光器能够获得更高的输出功率和转换效率。本文简要介绍了化学气相沉积法(CVD)制备的金刚石晶体的光学性质和热学特性,总结了基于人造金刚石晶体的拉曼激光器在紫外波段、可见光波段及红外波段的研究现状,并对其发展进行了展望。     

High fluence deposition of polyethylene glycol films at 1064 nm by matrix assisted pulsed laser evaporation (MAPLE)

Matrix assisted pulsed laser evaporation (MAPLE) has been applied for deposition of thin polyethylene glycol (PEG) films with infrared laser light at 1064 nm. We have irradiated frozen targets (of 1 wt.% PEG dissolved in water) and measured the deposition rate in situ with a quartz crystal microbalance. The laser fluence needed to produce PEG films turned out to be unexpectedly high with a threshold of 9 J/cm², and the deposition rate was much lower than that with laser light at 355 nm. Results from matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis demonstrate that the chemistry, molecular weight and polydispersity of the PEG films were identical to the starting material. Studies of the film surface with scanning electron microscopy (SEM) indicate that the Si-substrate is covered by a relatively homogenous PEG film with few bare spots.     

OES study of the gas phase during diamond films deposition in high power DC arc plasma jet CVD system

This paper used optical emission spectroscopy (OES) to study the gas phase in high power DC arc plasma jet chemical vapour deposition (CVD) during diamond films growth processes. The results show that all the deposition parameters (methane concentration, substrate temperature, gas flow rate and ratio of H₂/Ar) could strongly influence the gas phase. C₂ is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C₂ and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C₂ is presumed to be the main growth radical, and CH is also believed to contribute the diamond deposition.     

kHz激光器在武汉卫星观测站的测距实验

高重复频率激光器是kHz卫星激光测距系统的重要组成部分,提高激光发射频率可以有效地获得更多的观测数据,这是当今卫星激光测距领域的发展方向.针对武汉卫星观测站进行的kHz激光测距实验,介绍了kHz激光器的工作过程和原理,分析了影响高重复频率回波探测的因素.实验结果表明:对实验过程中所观测到的中低轨卫星,观测数据量提高了1...     

36.5 W high beam quality 532 nm green laser based on dual-rod AO Q-switched resonator

A high power, high beam quality, compact green laser based on dual-rod AO Q-switched resonator was designed, fabricated and tested. The laser provided a maximum 532 nm average power of 36.5 W at a repetition rate of 65 kHz with the beam quality factor of M² = 1.55 and the optical frequency conversion efficiency from NIR to green laser was as high as 51%. The pulse repetition rate was tunable from 50 kHz to 200 kHz and the overall dimension of the laser was within 500 × 300 × 150 mm³.