Detection of subsurface defects of fused silica optics by confocal scattering microscopy

<正>A non-destructive technique for subsurface measurements is proposed by combining light scattering method with laser confocal scanning tomography.The depth and distribution of subsurface defect layers are represented in term of scattered light intensity pattern,and three types of fused silica specimens are fabricated by different grinding and polishing processes to verify the validity and effectiveness.By using the direct measurement method with such technique,micron-scale cracks and scratches can be easily distinguished,and the instructional subsurface defect depths of 55,15,and 4μm are given in real time allowing for an in-process observation and detection.     

Off-Resonant Third-Order Optical Nonlinearity of Au Nanoparticle Array by Femtosecond Z-scan Measurement

A periodic triangular-shaped Au nanoparticle array is fabricated on a quartz substrate using nanosphere lithography and pulsed laser deposition, and the linear and nonlinear optical properties of metal particles are studied. The morphology of the polystyrene nanosphere mask （D = 820 nm） and the Au nanoparticle array are investigated by scanning electron microscopy. The surface plasmon resonance absorption peak is observed at 606 nm, which is in good agreement with the calculated result using the discrete dipole approximation method. By performing the Z-scan method with femtosecond laser （800 nm, 50 fs）, the optical nonlinearities of A u nanoparticle array are determined. The results show that the Au particles exhibit negative nonlinear absorption and positive nonlinear refractive index with the effective third-order optical nonlinear susceptibility Xeff^（3） can be up to （8.8 ± 1.0）× 10^-10 esu under non-resonant femtosecond laser excitation.     

Quantum phases of Bose gases on a lattice with pair-tunneling

We investigate the strongly interacting lattice Bose gases on a lattice with two-body interaction of nearest neighbors characterized by pair tunneling.The excitation spectrum and the depletion of the condensate of lattice Bose gases are investigated using the Bogoliubov transformation method and the results show that there is a pair condensate as well as a single particle condensate.The various possible quantum phases,such as the Mott-insulator phase(MI),the superfluid phase(SF) of an individual atom,the charge density wave phase(CDW),the supersolid phase(SS),the pair-superfluid(PSF) phase,and the pair-supersolid phase(PSS) are discussed in different parametric regions within our extended Bose-Hubbard model using perturbation theory.     

Direct manufacturing of Cu-based alloy parts by selective laser melting

The frequent defects of the metal parts, such as non-fully melting, thermal strain, and balling, which are produced by selective laser melting (SLM) that is a novel method of one-step manufacturing, are analyzed theoretically and experimentally. The processing parameters significantly affect the quality of the final parts, and simultaneously, the appropriate laser mode and the special scanning strategy assure a satisfying quality of the final parts. The SLM experiment is carried out using Cu-based powder. The metal part is divided into several scanned regions, each of which is scanned twice at the cross direction with different scanning speeds. The microstructure is analyzed on microscope. The results show that the part is metallurgically bonded entity with a relative density of 95%, and the microstructure is composed of equiaxial crystal and dendritic crystal whose distributions are mainly decided by the scanning strategy.     

Convenient method for calibrating system constant of scanning water vapor Raman lidar

<正>Lower tropospheric water vapor measurements are performed at nighttime using the mobile atmosphere monitoring lidar-2(AML-2) which is operated by the Anhui Institute of Optics and Fine Mechanics.In this lidar system,a 354.7-nm light from a Nd:YAG laser is used as stimulating source,whose Raman shifted center wavelengths are at 386.7 and 407.5 nm for nitrogen and water vapor,respectively.We present a novel and convenient method for determining the Raman lidar calibration constant according to the scanning performance of this lidar.We are likewise able to realize the measurement of water vapor profile in the low troposphere.The error induced by the uncertainty of calibrated constants is within 7% for the Raman lidar system.Experimental results from two months of study indicate that the method of calibrating the lidar system constant is feasible,and the Raman lidar performance is stable and reliable.     

Fluorescence molecular tomography system for in vivo tumor imaging in small animals

A fluorescence molecular tomography system for in vivo tumor imaging is developed using a 748-nm continuous wave diode laser as an excitation source.A high sensitivity cooled charge-coupled device (CCD) camera with excitation and emission filters is utilized to obtain the excitation and fluorescence images.The laser beam performs fast raster scanning using a dual-axis galvanometric scanner.The accuracy of the laser spot position at the source window is within ±200 μm.Based on the phantom experimental results,the spatial resolution is less than 1.7 mm,and the relative quantitation error is about 10%.In vivo imaging of a tumor-bearing nude mouse tagged with near-infrared dye demonstrates the feasibility of the system.     

Narrow-linewidth single-polarization frequency-modulated Er-doped fiber ring laser

We demonstrate a 1550-nm narrow-linewidth fiber ring laser with stable single polarization by using single-mode Er-doped fiber as active fiber and saturable absorber. A polarization-maintaining circulator is used to acquire single-polarization laser light with the degree of polarization of 99.8%--99.9%. The linewidth measured using a delayed self-heterodyne method is less than 0.5 kHz. Frequency of the fiber laser can be modulated by driving the waveguide phase modulator with proper voltage. A Mach-Zehnder interferometer with the optical path difference between two arms of about 36 km is used to study the long-distance coherent detection of the fiber laser for frequency-modulated continuous-wave application.     

Spectral filtering of dual lasers with a high-finesse length-tunable cavity for rubidium atom Rydberg excitation

We propose and demonstrate an alternative method for spectral filtering and frequency stabilization of both 780-nm and 960-nm lasers using a high-finesse length-tunable cavity(HFLTC). Firstly, the length of HFLTC is stabilized to a commercial frequency reference. Then, the two lasers are locked to this HFLTC using the Pound–Drever–Hall(PDH) method which can narrow the linewidths and stabilize the frequencies of both lasers simultaneously. Finally, the transmitted lasers of HFLTC with each power up to about 100 μW, which act as seed lasers, are amplified using the injection locking method for single-atom Rydberg excitation. The linewidths of obtained lasers are narrowed to be less than 1 k Hz, meanwhile the obtained lasers' phase noise around 750 k Hz are suppressed about 30 d B. With the spectrally filtered lasers, we demonstrate a Rabi oscillation between the ground state and Rydberg state of single-atoms in an optical trap tweezer with a decay time of(67 ± 37) μs, which is almost not affected by laser phase noise. We found that the maximum short-term laser frequency fluctuation of a single excitation lasers is at ～ 3.3 k Hz and the maximum long-term laser frequency drift of a single laser is ～ 46 k Hz during one month. Our work develops a stable and repeatable method to provide multiple laser sources of ultra-low phase noise, narrow linewidth, and excellent frequency stability, which is essential for high precision atomic experiments, such as neutral atom quantum computing, quantum simulation, quantum metrology, and so on.     

Villain Transformation for Ferrimagnetic Spin Chain

By using the Villain transformation, the Heisenberg ferrimagnetic spin chain is calculated. Two branches of the low-lying excitation in both the absence and presence of magnetic field are obtained. The thermodynamic quantities （such as free energy, magnetization, specific heat and static magnetic susceptibility） are also evaluated at finite temperature. This ＆ the first time to calculate the Ferrimagnetic spin chain by using Villain＇s method, and we find that the results at a low temperature are quite similar to the previous calculation. The results of free energy and magnetization in zero temperature suggest that the Villain transformation has a good efficiency.     

Baecklund Transformations for the Initial Problems of Nizhnich and Nizhnich－Novikov－Veselov Equations

The homogeneous balance method is a method for solving genera/partial differential equations (PDEs). In this paper we solve a kind of initial problems of the PDEs by using the special Baecklund transformations of the initial problem. The basic Fourier transformation method and some variable-separation skill are used as auxiliaries. Two initial problems of Nizlmich and the Nizlanich-Novikov-Veselov equations are solved by using this approach.     

Laser-based linear and nonlinear guided elastic waves at surfaces (2D) and wedges (1D)

The characteristic features and applications of linear and nonlinear guided elastic waves propagating along surfaces (2D) and wedges (1D) are discussed. Laser-based excitation, detection, or contact-free analysis of these guided waves with pump–probe methods are reviewed. Determination of material parameters by broadband surface acoustic waves (SAWs) and other applications in nondestructive evaluation (NDE) are considered. The realization of nonlinear SAWs in the form of solitary waves and as shock waves, used for the determination of the fracture strength, is described. The unique properties of dispersion-free wedge waves (WWs) propagating along homogeneous wedges and of dispersive wedge waves observed in the presence of wedge modifications such as tip truncation or coatings are outlined. Theoretical and experimental results on nonlinear wedge waves in isotropic and anisotropic solids are presented.     

Ultrafast magneto-optics in nickel: magnetism or optics?

Several magnetic and optical processes contribute to the magneto-optical response of nickel thin films after excitation by a femtosecond laser pulse. We achieved a first complete identification by explicitly measuring the time-resolved Kerr ellipticity and rotation, as well as its temperature and magnetic field dependence in epitaxially grown (111) and (001) oriented Cu/Ni/Cu wedges. The first hundreds of femtoseconds the response is dominated by state filling effects. The true demagnetization takes approximately 0.5-1 ps. At the longer (sub-ns) time scales the spins are found to precess in their anisotropy field. Simple and transparent models are introduced to substantiate our interpretation.     

一种用多色光作为激发源产生拉曼光谱的新算法

探讨用多色光代替激光作为拉曼光源的新型拉曼光谱仪的可能性.根据拉曼光谱原理,并通过数学分析,发现当用多色光照射在样品上时,所得到的散射光经散射频率校正后在不同频率上的强度分布可以写成样品的Raman-Rayleigh联合散射谱和激发光光源的功率谱的卷积.利用傅里叶变换算法,有可能从多色光照射样品所得到的散射光谱中导出样品的拉曼光谱.基于上述原理,可能发展出不用激光的新一代拉曼光谱仪.     

线激光束均匀化整形方法研究

为解决核物理工程、表面热处理、激光加工、激光通信中传输激光束的均匀性问题,提出采用三角楔柱透镜改善线激光均匀性的新方法,并在ZEMAX开发环境下建立了整形光路系统的理论模型。利用所建立的模型,分析了整形柱透镜在不同半径、斜面夹角、透镜介质折射率等参数下光束的均匀性。研究表明：在远场条件下,通过改变整形柱透镜的参数,能够得到能量分布均匀的线激光。在实际应用中,可以采用1个半圆柱和2个相同三角楔胶合成型的简单工艺。进一步模拟发现,两种整形系统所得到的均匀度和线宽一致。     

多光子激发荧光与毛细管电泳联用的实验研究

将多光子激发荧光探测与毛细管电泳技术相结合,研制了多光子激发荧光 毛细管电泳联用装置。这种方法可以高效快速的分离检测复杂样品中多种不同的荧光分子。作者对5HT ,FAD ,NADH这三种重要的生物分子,不用染料标记,分别用双光子激发和三光子激发,进行了直接的分离、识别和检测。得到的检测限分别是5HT 1. 0×10 -6mol·L-1,FAD 7. 4×10 -7mol·L-1,NADH 9. 8×10 -7mol·L-1。5HT的检测限比紫外吸收低2个数量级;FAD和NADH的检测限比紫外吸收低1个数量级。     

Selecting molecules embedded in nanodroplets (clusters) of superfluid helium

A method of selecting molecules embedded in nanodroplets (clusters) of superfluid helium is proposed, which is based on the selective vibrational excitation of embedded molecules by intense IR laser radiation. This action leads to a significant decrease in size of the excited clusters, after which these clusters are separated with respect to size via scattering of the cluster beam on a crossing atomic beam. The method is described in detail and the possibility of selecting SF₆ molecules in liquid helium nanodroplets using the excitation by CO₂ laser radiation and the angular separation via scattering on a xenon atomic beam is demonstrated. The results show that, by using this technique, it is possible to separate molecules with respect to isotope (element) composition. Advantages and drawbacks of the method are analyzed.     

Vibration testing based on impulse response excited by laser ablation

This paper proposes an innovative vibration testing method based on impulse response excited by laser ablation. In conventional vibration testing using an impulse hammer, high-frequency elements of over tens of kilohertz are barely present in the excitation force. A pulsed high-power YAG laser is used in this study for producing an ideal impulse force on a structural surface. Illuminating a point on a metal with the well-focused YAG laser, laser ablation is caused by generation of plasma on the metal. As a result, an ideal impulse excitation force generated by laser ablation is applied to the point on the structure. Therefore, it is possible to measure high-frequency FRFs due to the laser excitation. A water droplet overlay on the metal is used to adjust the force magnitude of laser excitation. An aluminum block that has nine natural frequencies below 40 kHz is employed as a test piece. The validity of the proposed method is verified by comparing the FRFs of the block obtained by the laser excitation, impulse hammer, and finite element analysis. Furthermore, the relationship between accuracy of FRF measurements and sensitivity of sensors is investigated.     

激光激励下镝离子掺杂氟硼酸盐玻璃荧光体的辐照参数

采用高温熔融法制备了镝离子掺杂氟硼酸盐玻璃荧光体，利用积分球绝对光谱测试系统，在453 nm蓝色激光二极管激发下，对玻璃荧光体的荧光光谱进行表征，解析出玻璃荧光体的相关绝对荧光参量。测试与计算结果表明，1.0 Wt% Dy₂O₃掺杂玻璃荧光体在功率15.81 mW的蓝色激光激发下，净发射光谱功率是286.91 μW，发射光子数为17.17×1014 cps，其荧光量子产率达到25.86%。为提高玻璃荧光体对泵浦激光的利用率，减少残余激光成分，进而改善组合光品质，制备了大体积的1.5 Wt% Dy₂O₃掺杂玻璃荧光体，在高功率的蓝色激光激发下获得白色照明效果，该玻璃荧光体在激发功率分别为56.0和252.7 mW的激光激发下，组合荧光对应的色坐标分别是(0.316, 0.287)和(0.303，0.268)。激光激励下的高效白色发光表明Dy3+掺杂氟硼酸盐玻璃荧光体在激光照明领域具有良好的应用前景。     

Single-beam thermowave analysis of semiconductors

The paper describes a new single-beam thermowave technique based on a two-frequency modulation of the laser beam used for both excitation and detection of the photothermal response in a sample. This technique provides frequency transformation to the low-frequency region and, to a certain degree, phase sensitivity without applying the lock-in detection method. This single-beam technique is proved to yield substantial evidence in the field of laser annealing of semiconductors such as the annealing threshold, the defects generated by the ultrafast solidification and the homogeneity of the laser beam applied for irradiation.