Continuous scanning, laser imaging velocimetry

Careful exploitation of the anisotropy native to late time stratified and rotating flows permits the use of a laser scanning measurement technique to simultaneously resolve the 2D velocity field in O(100) slices. The technique relies on getting the Reynolds number from the length scale while keeping the velocity small, this provides a characteristic time scale that is sufficiently large to permit full 3D scanning through the measurement volume in a relatively short time. As the vertical velocity component of these late time stratified flows is effectively zero, all components of the deformation tensor are resolved. 3D, time resolved measurements of the vorticity and enstrophy fields associated with stratified rotating flows such as vortex dipoles, monopoles and wakes are presented.     

Near-field optical microscope with a multiheight scanning imaging mode

A near-field scanning optical microscope has been developed to yield optical images with various gap distances between the probe and the sample surface. The microscope uses an apertureless metallic probe, the position of which is controlled by regulation of the tunneling-electron current from the probe to the sample and by computer-generated bias voltage. Experimental results of near-field optical imaging with the developed microscope at different gap distances are shown. Thirteen images at gap distances of 0 to 500nm demonstrate that the near-field image depends strongly on the gap distance. The imaging characteristics of a near-field imaging system are shown with the spatial-frequency spectra of images. Future investigation of the developed microscope is also discussed.     

Automatic vibration mode tracking using a scanning laser Doppler vibrometer

Optical measurement techniques are being used more and more for quality control in the production process. An important problem when trying to implement optical measurement systems, and in particular the scanning laser Doppler vibrometer (SLDV) which is considered in this paper, is that user interaction is always required. The need for user interaction implies an increase in testing time and cost and also brings an additional source of variability of the test results. In this article, a completely autonomous test procedure is developed to track the vibration behavior of a product during the production process (this includes automatic laser focussing, position calibration, object recognition, grid generation and mode estimation). The proposed procedure typically requires a few minutes only to automatically determine a high-resolution model of the vibration behavior. The method will be validated on measurements of an electronic circuit board.     

Synthetic aperture laser optical feedback imaging using galvanometric scanning

We describe a new one-dimensional synthetic aperture imaging laser radar (ladar) using the resonant sensitivity of a microchip laser to frequency-shifted optical feedback and galvanometric scanning of the target under investigation. In our experiment, the laser is both the source and the detector, providing optical amplification with self-aligned heterodyne detection. By using galvanometric scanning, we achieve an along-track spatial resolution better than the diffraction limit.     

Second harmonic imaging of chloroplasts using the two-photon laser scanning microscope

BackgroundSecond harmonic information reveals information about the structure of spatially oriented structures with an asymmetry. We study the second harmonic images of the grana and intergranal parts of chloroplasts in the leaves of the shade moss Plagiomnium affine.ResultsA two-photon microscope with blocking filters to suppress fluorescence generated both forward and backward second harmonic illumination to be captured. In the starch free chloroplasts of the single cell layered laminae strong second harmonic generation (SHG) from the granal regions was emitted. Upon illumination the chloroplasts changed their orientation affecting the SHG signal. Chloroplast is reoriented upon illumination.ConclusionsSHG signals were successfully obtained from the grana without any possible confusion from SHG starch grains due to their absence.     

Effect of the modulation waveform on the S/N ratio of laser scanning imaging systems

In a laser scanning imaging system, the modulation of light output is directly achieved by modulating the drive current of a laser diode input signal. So far, what kind of modulation waveform is the best remains undetermined. People usually choose sine modulation for convenience. Through our theoretical analysis and experiment, we have reached the conclusion that for the same receiver, substituting low duty (a duty of is small enough) rectangular modulation for conventional sine modulation will offer at least a 5 dB improvement in S/N ratio with the average incident optical power unchanged.     

Standard artifact for the geometric verification of terrestrial laser scanning systems

Terrestrial laser scanners are geodetic instruments with applications in areas such as architecture, civil engineering or environment. Although it is common to receive the technical specifications of the systems from their manufacturers, there are not any solutions for data verification in the market available for the users. This work proposes a standard artifact and a methodology to perform, in a simple way, the metrology verification of laser scanners.The artifact is manufactured using aluminium and delrin, materials that make the artifact robust and portable. The system consists of a set of five spheres situated at equal distances to one another, and a set of seven cubes of different sizes. A coordinate measuring machine with sub-millimetre precision is used for calibration purposes under controlled environmental conditions. After its calibration, the artifact can be used for the verification of metrology specifications given by manufacturers of laser scanners.The elements of the artifact are destinated to test different metrological characteristics, such as accuracy, precision and resolution. The distance between centres of the spheres is used to obtain the accuracy data, the standard deviation of the top face of the largest cube is used to establish the precision (repeatability) and the error in the measurement of the cubes provides the resolution value in axes X, Y and Z. Methodology for the evaluation is mainly supported by least squares fitting algorithms developed using Matlab programming.The artifact and methodology proposed were tested using a terrestrial laser scanner Riegl LMSZ-390i at three different ranges (10, 30 and 50 m) and four stepwidths (0.002°, 0.005°, 0.010° and 0.020°), both for horizontal and vertical displacements. Results obtained are in agreement with the accuracy and precision data given by the manufacturer, 6 and 4 mm, respectively. On the other hand, important influences between resolution and range and between resolution and stepwidth are observed. For example, the two smaller cubes cannot be well detected in any case and, as must be expected, the increase in range and stepwidth produces a decrease in the quality of the detection for the larger ones.     

Dual mode near-field scanning optical microscopy for near-field imaging of surface plasmon polariton

In this paper, we theoretically and experimentally demonstrate that metal coated apertured probes are efficient near-field probes on surfaces with high reflectivity for the scattering as well as for the collection mode near-field scanning optical microscopy (NSOM). We show that a blunt apertured metal coated tip is very effective in suppressing image dipoles which affect strongly the signals scattered from frequently used sharp metal tips or gold nanoparticle attached probes. By using a simultaneous collection and scattering mode (dual mode) NSOM we measure the near-field images of surface plasmon polariton (SPP) launched from a slit. The collection mode measures propagating SPP along lateral distance in a long scan range with high signal-to-noise ratio, and the scattering mode measures the polarization resolved near-field of SPP. Comparisons of the measured data obtained in the dual mode enable to easily characterize SPP and to separate the measured near-field into the propagating SPP and the directly transmitted light.     

Large field of view MEMS-based confocal laser scanning microscope for fluorescence imaging

Although confocal fluorescence microscopes are widely used in biology and have been proven to be promising diagnostic tools in dermatologic diagnostics, they are at present uncommon in medical practice. This is mainly due to high costs of acquisition and their large and complex outline. With the integration of a MEMS scanner we present a demonstration system of a confocal fluorescence laser scanning microscope which is affordable and portable. It has a field of view of 500 μm × 500 μm and is mainly composed of off-the-shelf components.     

Simultaneous imaging of human cone mosaic with adaptive optics enhanced scanning laser ophthalmoscopy and high-speed transversal scanning optical coherence tomography

We describe a novel instrument capable of acquiring, simultaneously, adaptive optics enhanced scanning laser ophthalmoscopy and optical coherence tomography (OCT) images of the human cone mosaic in vivo. The OCT system is based on transversal scanning of the sample with a line scan rate of 14 kHz, approximately 20 times faster than a previously reported instrument. We demonstrate the capability of this instrument with the measurement of the human cone spacing in perifoveal retina.     

Interferometric scanning of laser beams

A new beam deflection technique is based on modulating the optical transmission characteristics of a modified Fabry-Perot interferometer. Electro-optically changing the interferometer length leads to fast high resolution scanning of the transmission fringe. Experiments have been conducted using the 4880 Å argon laser line with an interferometer containing a LiNbO₃ crystal.     

Bimorph deformable mirror based adaptive optics scanning laser ophthalmoscope for retina imaging in vivo

A bimorph deformable mirror(DM) with a large stroke of more than 30 μm using 35 actuators is presented and characterized for an adaptive optics(AO) confocal scanning laser ophthalmoscope application. Facilitated with a Shack–Hartmann wavefront sensor, the bimorph DM-based AO operates closed-loop AO corrections for human eyes and reduces wavefront aberrations in most eyes to below 0.1 μm rms. Results from living eyes, including one exhibiting ～5D of myopia and ～2D of astigmatism along with notable high-order aberrations, reveal a practical efficient aberration correction and demonstrate a great benefit for retina imaging, including improving resolution, increasing brightness, and enhancing the contrast of images.     

Developing a contact probe for rodent fundus imaging in a confocal scanning laser ophthalmoscope

Since significant ocular differences in both anatomical structure and optical properties exist between rodents and humans, clinical imaging devices for human use are not suitable for use on rodents. In this study, we develop a contact probe with a flexible surface that can closely fit the rodent cornea for fundus imaging with a confocal scanning laser ophthalmoscope. Both Zemax simulation and in vivo fundus imaging demonstrate that this contact probe can significantly improve both the imaging quality and the operational convenience.     

Grating imaging scanning lithography

We present a grating imaging scanning lithography system for the fabrication of large-sized gratings. In this technology, ±1-order diffractive beams are generated by a phase grating and selected by a spatial filter. Meanwhile, a 4f system enables the ±1-order diffractive beams to form a grating image with a clear jagged-edge boundary on the substrate. A high-precision two-dimensional （2D） mobile stage is used for complementary cyclical scanning, thereby effectively eliminating image stitching errors. The absence of such errors results in a seamless and uniform large-sized grating. Characterized by a simple structure, high energy use, and good stability, this lithography system is highly relevant to the high-speed and cost- effective production of large-sized gratings.     

Fast-scanning two-photon fluorescence imaging based on a microelectromechanical systems two- dimensional scanning mirror

Towards overcoming the size limitations of conventional two-photon fluorescence microscopy, we introduce two-photon imaging based on microelectromechanical systems (MEMS) scanners. Single crystalline silicon scanning mirrors that are 0.75 mm x 0.75 mm in size and driven in two dimensions by microfabricated vertical comb electrostatic actuators can provide optical deflection angles through a range of approximately16 degrees . Using such scanners we demonstrated two-photon microscopy and microendoscopy with fast-axis acquisition rates up to 3.52 kHz.     

Enhancing the resolution of the forward second harmonic imaging using the two-photon laser scanning microscope

The effect of increasing the numerical aperture and changing the immersion imaging medium of the objective in the forward second harmonic imaging of the grana and intergranal parts of chloroplasts in the leaves of shade moss Plagiomnium affine plant were demonstrated. Also the enhancement of the forward second harmonic generation images and simultaneously records the forward and backward second harmonic signals were demonstrated. The second harmonic signals in the forward and backward directions are generated by a tightly focused linearly polarized femtosecond pulses laser.

Conclusions

Forward second harmonic signals were successfully enhanced by capturing higher order of diffraction rays from the samples using high numerical aperture water immersion objective.     

基于线扫方式的静压气浮激光点云数据扫描误差修正方法研究

为了修正静压气浮激光点云数据扫描误差,提出了一种基于不同扫描速度下所采集的点云数据,通过最小二乘法分区间建立误差预测模型实现对相应误差修正的新方法。实验结果表明,静压气浮三维测量仪的测量精度随气浮导轨扫描速度变化在特定范围内基本呈二次曲线变化关系,该误差修正方法能够快速、准确地实现静压气浮激光点云数据扫描误差的修正,具有较大的适用性和实际参考价值。     

Collection mode near-field scanning microwave microscopy

Collection mode near-field microscopy is demonstrated using a 10.56 GHz (X-band) frequency illumination. Imaging of a standing evanescent microwave was experimentally used to evaluate the capabilities of the microscope. The microscope functionality was validated by imaging near field interactions of different systems of dipole-like resonances. We prove that those microscope images contain near-field information by presenting numerical modeling of dipole-like resonant interactions. The model makes use of an analytic Dyadic Green's which is based in the near-field electrostatic approximation. We propose that this microscopy technique can be used, with certain limitations, as a check for 2D mapping of designed (spoof) surface plasmon at microwave frequencies.     

新型自扫描激光干涉系统

本文介绍了一种新型自扫描激光干涉系统的原理和结构。该系统采用自扫描光电二极管列阵（以下简称ＳＳＰＤＡ）接收器件，实现对干涉仪信号的调制，使测量信号转换成交流信号，避免了直流放大器零点漂移，消除了低频干扰。实验证明，该系统在采用普通器件的情况下，其分辨率优于０．０２μｍ。