基于双声光移频器的外差式激光多普勒测振计

分析了单声光移频器构成的外差式激光多普勒测振计中声光移频器驱动信号的频率稳定性和信号功率对待测振动信号的影响.为了降低声光移频器驱动信号频率漂移的影响,提出双声光移频器构成的外差式激光多普勒测振计,并基于直接数字频率合成技术,以相位噪音低、初始相位可控的芯片AD9912为核心器件,完成了声光移频器驱动信号生成及处理模块的设计.开展了双声光移频器组成的外差式激光多普勒测振计的振动测量实验,结果表明,驱动信号生成装置可以驱动声光移频器正常工作,且测振计的本底噪音在0~10kHz频带范围内呈现平坦分布,0~1kHz频段内噪音得到明显抑制,较单声光移频器构成的外差式激光多普勒测振计有显著改善.     

基于双声光移频器的外差式激光多普勒测振计

分析了单声光移频器构成的外差式激光多普勒测振计中声光移频器驱动信号的频率稳定性和信号功率对待测振动信号的影响.为了降低声光移频器驱动信号频率漂移的影响,提出双声光移频器构成的外差式激光多普勒测振计,并基于直接数字频率合成技术,以相位噪音低、初始相位可控的芯片AD9912为核心器件,完成了声光移频器驱动信号生成及处理模块的设计.开展了双声光移频器组成的外差式激光多普勒测振计的振动测量实验,结果表明,驱动信号生成装置可以驱动声光移频器正常工作,且测振计的本底噪音在0～10kHz频带范围内呈现平坦分布,0～1kHz频段内噪音得到明显抑制,较单声光移频器构成的外差式激光多普勒测振计有显著改善.     

环境温度宽范围变化对光纤布里渊频移的影响

搭建了光纤布里渊频移测量系统,实现了色散位移光纤20 ℃到820 ℃布里渊频移的测量,并对测量数据进行拟合. 在环境温度大范围变化时,目前采用的布里渊频移-温度一阶线性关系式对测量数据分析误差较大,针对这个问题,本文从纯石英光纤的结构特点和材料的物性系数出发,在分析光纤的热膨胀系数、光纤密度、折射率、弹性模量和泊松比与宽范围温度关系的基础上,根据布里渊频移与各物性参数的关系式理论推导了宽范围温度变化与布里渊频移之间的二次项关系式. 理论推导结果与实验数据基本符合,验证了理论分析的正确性,从而为光纤宽范围布 关键词： 光纤 高温传感 布里渊散射 布里渊频移     

利用啁啾激光调制分子谐波信号

数值研究了啁啾激光驱动H_2~+辐射谐波的特点.结果表明,(1)在低强度和高强度激光驱动下,谐波光谱分别呈现红移和蓝移现象.引入正负向啁啾参数后,谐波频移和谐波辐射强度都可以得到调控.(2)谐波光谱在高强度激光驱动下呈现非奇次谐波.理论分析表明,非奇次谐波产生的原因是双H核频移不一致所导致的不对称相消干涉引起的.     

用于面形测量的光纤投影器相移和频移特性

提出了一种光纤投影器产生相移和频移的方法,给出了光纤投影器相移和频移特性的理论与实验相一致的结果。光纤投影器利用双光束干涉产生正弦调制的结构光场,通过在一路光中引入压电陶瓷PZT,调节PZT的驱动电压来改变双光纤中光波的光程差,从而使干涉条纹产生相移,得到相移随驱动电压的变化曲线;频移是采用移动光纤投影器到接收屏距离的方法来改变干涉光场的空间频率,给出了变频条纹的傅里叶频谱,得到干涉光场的相对空间频率,将其与理论值相比较,给出二者之间的线性关系曲线,从而证明了干涉光场相对空间频率与投影器到接收屏距离成反比的关系。     

基于级联型光纤的孤子自频移增强特性

设计了一种10m掺铥光纤级联于3m大模场光子晶体光纤末端的结构,利用400fs、1 550nm脉冲光产生孤子自频移,在入射光功率相同的情况下,掺铥光纤末端的孤子频移量比大模场光纤末端多100~150nm,平均多30%左右.孤子与泵浦光在掺铥光纤末端的输出光谱表明,残留泵浦光作用于Tm3+,在1.8~2.1μm范围产生受激辐射,从而增强了拉曼效应,导致孤子自频移增强.实验结果揭示了一种增强孤子自频移效应的方法,对于了解孤子在光纤中频移特性和提高基于孤子自频移的可调谐光源的调谐范围等具有参考意义.     

掺杂和结构对光纤中去极化型声波导布里渊散射频移与散射效率的影响

利用全矢量有限元法研究了单模光纤及光子晶体光纤中掺杂材料及浓度、光纤结构对去极化型声波导布里渊散射频移和散射效率的影响.结果表明增大包层掺氟浓度或纤芯掺锗浓度均会减小光纤布里渊频移,也会增大单模光纤散射效率.光子晶体光纤中整体掺氟浓度不变时,空气孔层数的增加会减小布里渊频移;而纤芯掺锗浓度不变时,随空气孔层数的增加TR2,3模式的布里渊频移增大,而TR2,7模式的布里渊频移减小.     

一种利用布里渊散射的光纤应变传感应方法

根光纤史的布里渊散射附加频移与光纤所受的拉伸应奕有关的特性,推导了附加频移与应变间的线性关系。在此基础上上提出了利用光外差原理探测附加频移,从而实现应变探测的传感新方案,并分析了该方案能降低对激光源的线宽及频率稳定要求之原因,给出了实验系统及实验结果。     

一种利用布里渊散射的光纤应变传感新方法

根据光纤中的布里渊散射附加频移与光纤所受的拉伸应变有关的特性,推导了附加频移与应变间的线性关系。在此基础上提出了利用光外差原理探测附加频移,从而实现应变探测的传感新方案,并分析了该方案能降低对激光源的线宽及频率稳定度要求之原因,给出了实验系统及实验结果。     

孤子光纤中拉曼自频移效应的研究

首次报道孤子光纤中拉曼自频移效庆的研究结果。对满足孤子光纤色散关系条件时含损耗，拉曼延迟效应的广义非线性薛定谔方程进行了微扰分析。求得了拉曼自频移关系表达式。发现改变光纤几何参数可以有效地控制孤子拉曼自频移。     

Metal catalyst-assisted growth of GaN nanowires on graphene films for flexible photocatalyst applications

We report the growth of high-areal-density GaN nanowires on large-size graphene films using a nickel (Ni) catalyst-assisted vapor-liquid-solid (VLS) method. Before the nanowire growth, the graphene films were prepared on copper foils using hot-wall chemical vapor deposition and transferred onto SiO₂/Si substrates. Then, for catalyst-assisted VLS growth, Ni catalyst layers with thickness of a few nanometers were deposited on the graphene-coated substrates using a thermal evaporator. We investigated the effect of the Ni catalyst thickness on the formation of GaN nanowires. Furthermore, the structural and optical characteristics of GaN nanowires were investigated using X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The GaN nanowires grown on graphene films were transferred onto polymer substrates using a simple lift-off method for applications as flexible photocatalysts. Photocatalysis activities of the GaN nanowires prepared on the flexible polymer substrates were investigated under bending conditions.     

Preliminary study on rotary ultrasonic machining of CFRP/Ti stacks

Reported drilling methods for CFRP/Ti stacks include twist drilling, end milling, core grinding, and their derived methods. The literature does not have any report on drilling of CFRP/Ti stacks using rotary ultrasonic machining (RUM). This paper, for the first time, reports a study on drilling of CFRP/Ti stacks using RUM. It also compares results on drilling of CFRP/Ti stacks using RUM with reported results on drilling of CFRP/Ti stacks using other methods. When drilling CFRP/Ti stacks using RUM, cutting force, torque, and CFRP surface roughness were lower, hole size variation was smaller, CFRP groove depth was smaller, tool life was longer, and there was no obvious Ti exit burr and CFRP entrance delamination. Ti surface roughness when drilling of CFRP/Ti stacks using RUM was about the same as those when using other methods.     

利用激光微束力学效应操纵生物体的实验研究

用光线光学方法对光束作用于微粒的力学问题进行分析,着重介绍了利用激光微束力学效应对多种生活活性细胞进行操纵的实验研究。     

Membrane device for holding biomolecule samples for terahertz spectroscopy

A device for holding biomolecule samples on a membrane allows scanning using terahertz frequency waves. Such scanning has previously been difficult due to the strong attenuation of terahertz frequency waves by water. Several types of biomolecules were scanned using terahertz time domain spectroscopy (TDS), and the data showed clear differences in transmittance among the samples. This membrane device is a promising aid for research on biomolecules using terahertz waves.     

Generation of squeezed vacuum on cesium D2 line down to kilohertz range

We report the experimental generation of a squeezed vacuum at frequencies ranging from 2.5 kHz to 200 kHz that is resonant on the cesium D2 line by using a below-threshold optical parametric oscillator(OPO). The OPO is based on a periodically-poled KTiOPO_4(PPKTP) crystal that is pumped using a bow-tie four-mirror ring frequency doubler. The phase of the squeezed light is controlled using a quantum noise locking technique. At a pump power of 115 mW, maximum quadrature phase squeezing of 3.5 d B and anti-squeezing of 7.5 d B are detected using a home-made balanced homodyne detector. This squeezed vacuum at an atomic transition in the kilohertz range is an ideal quantum source for quantum metrology of enhancing measurement precision, especially for ultra-sensitive measurement of weak magnetic fields when using a Cs atomic magnetometer in the audio frequency range.     

Freestanding graphene writing on a silicon carbide wafer

Freestanding graphene on a trench has been fabricated extensively using a transfer process of chemical vapor deposition grown graphene. Here, we demonstrate that freestanding graphene can be grown directly on a trench without a transfer process. A shallow trench was made on a 6H–SiC(0001) wafer using a focused ion beam lithography. The shallow trench was heated to a high temperature under Ar atmosphere. The heat treatment made the shallow trench become deeper and wider. Subsequently, epitaxial graphene was floating on the trench, resulting in freestanding graphene, where underlying bulk SiC was self-etched after the growth of epitaxial graphene. The freestanding graphene on a trench was characterized using Raman spectroscopy and atomic force microscopy. Such freestanding graphene writing can be applied to semiconductor fabrication process of freestanding graphene devices without a transfer process.     

An infrared spectroscopic investigation of thin alumina films: measurement of acid sites and surface reactivity

The surface chemical activity of an alumina films grown on Mo(100) by oxidation of aluminum evaporated onto the surface and oxidized using water is examined using Auger, X-ray photoelectron and reflection/absorption infrared spectroscopies. The formation of alumina is confirmed using Auger and X-ray photoelectron spectroscopy from the positions and intensities of the aluminum features and using reflection-absorption infrared spectroscopy from the longitudinal optical modes of the Al–O bonds measured at 935 cm⁻¹. The presence of surface hydroxyls is monitored by forming films using D₂O which are evidenced by a feature at 2700 cm⁻¹. Ammonia adsorption on a dehydroxylated surface yields a single peak at 1260 cm⁻¹ due to ammonia adsorbed at a surface Lewis site where the principle symmetry axis of ammonia is oriented perpendicularly to the surface plane. Ammonia also appears to adsorb at Lewis sites on a hydroxylated surface with a slightly different adsorption geometry from that on a dehydroxylated surface. Finally, the chemistry of trimethyl aluminum adsorbed on the planar hydroxylated alumina surface is compared with that found on high-surface-area γ-alumina where the spectra and the chemistry found in both régimes is exactly identical except that the low-frequency methyl bending modes (at 769 and 718 cm⁻¹) are not obscured on the thin film by the intense substrate whereas they are on the high-surface-area support.     

滴状冷凝中液滴的内外压差及临界半径

用热力学方法证明了壁面上球冠形液滴的内外压差同样遵循经典的Laplace方程,并用力学方法给予了验证.液滴的内外压差与固液接触角无关,只取决于液体的表面张力和液滴半径;液滴的临界半径也与接触角无关,其值可用经典的Kalvin公式计算 关键词： 滴状冷凝 液滴 压差 临界半径     

Immobilization of protein molecules on step-controlled sapphire surfaces

We have studied effects of surface morphology on immobilization of protein molecules using step-controlled sapphire surfaces. Preferential adsorption of avidin molecules on the step edges was observed on the single-stepped sapphire surface. A randomly-stepped sapphire surface was found to be suitable for high-density immobilization of protein molecules. These results indicate atomic scale structures of the substrate surface influence the adsorption efficiency of the proteins. By using an atomic force microscopy (AFM) equipped with a biotin-modified cantilever, we have confirmed that the immobilized avidin molecules on the substrates keep their biological activity. This means that the ligand-receptor interaction can be detected using the phase image mode of a standard AFM.