Metasurfaces provide great feasibilities for tailoring both propagation waves and surface plasmon polaritons (SPPs). Manipulation of SPPs with arbitrary complex field distribution is an important issue in integrated nanophotonics due to their capability of guiding waves with subwavelength footprint. Here, with metasurface composed of nano aperture arrays, a novel approach is proposed and experimentally demonstrated which can effectively manipulate complex amplitude of SPPs in the near-field regime. Positioning the azimuthal angles of nano aperture arrays and simultaneously tuning their geometric parameters, the phase and amplitude are controlled based on Pancharatnam-Berry phases and their individual transmission coefficients. For the verification of the proposed design, Airy plasmons and axisymmetric Airy beams are generated. The results of numerical simulations and near-field imaging are well consistent with each other. Besides, 2D dipole analysis is also applied for efficient simulations. This strategy of complex amplitude manipulation with metasurface can be used for potential applications in plasmonic beam shaping, integrated optoelectronic systems and surface wave holography.
A nanometric bow-tie aperture has a resonant wavelength where its power throughput is maximal. The incident wavelength should coincide with the resonant wavelength in order to improve the power throughput. However, sometimes it is impossible to tune the incident wavelength, so the resonant wavelength should be tuned alternatively. In order to implement this goal, the relative permittivity of the dielectric substrate of the bow-tie aperture was altered. Finite-difference time-domain (FDTD) simulation results demonstrated that the resonant wavelength is tuned from 569.7 nm to 694.1 nm when the relative permittivity is altered from 1.0 to 3.5. The advantage of this method is that the resonant wavelength can be tuned continuously if the relative permittivity can be altered continuously.
KEYWORDS: Particles, Silver, Finite-difference time-domain method, Near field, Near field optics, Multiple scattering, Super resolution, Metals, Laser ablation, Near field scanning optical microscopy
Random Ag-SiN films consisting of random small Ag particles embedded in a SiN thin film were deposited by radiant-frequency magnetron sputtering. Specimens orderly comprising a random Ag-SiN film and an optical phase change recording layer were exposed to a focused laser beam. It showed that, with a random Ag-SiN layer deposited above the recording layer, the ablation of the recording layer occurred much faster and under much lower power than that of a single recording layer, which verified the local field enhancement of multiple scattering effects of the Ag particles. Finite Difference Time Domain (FDTD) calculation of a sandwiched structure consisting of ZnS-SiO2(130nm)/AgOx(20nm)/ZnS-SiO2(40nm) under a Gaussian beam irradiation has been carried out to simulate the near-field distribution in the structure. Near-field optical data storage adopting a Super-Resolution Near-field Structure (Super-RENS) usually utilizes similar films structure mentioned above to achieve super resolution storage density while getting a high Carrier to Noise Ratio (CNR) at the same time. Many recent works have reported that small Ag particles were formed in the AgOx film after converging laser irradiation onto the sandwiched structure. Here, another FDTD calculation was done to simulate the same model except for that small Ag particles were modeled in the AgOx film in the center region of the incident laser spot. The results showed a huge local near-field enhancement, which indicates that, if the structure full of such small Ag particles are formed in a tiny region beyond the optical diffraction limit, the optical recording and readout out density would be improved as well as a high CNR level achieved due to the multiple scattering of the Ag particles.
KEYWORDS: Gold, Near field, Finite-difference time-domain method, Light sources, Near field optics, Optical storage, Optical imaging, Near field scanning optical microscopy, Numerical simulations, Super resolution
In this paper the near-field distributions of bow-tie apertures in visible range are characterized by the method of 3D finite-difference time-domain (FDTD). The numerical simulation results reveal theoretically the relation of field enhancement effect of bow-tie aperture and its several parameters including tip angle, aperture size and film thickness. For the bow-tie aperture with a certain tip angle, the metallic film's thickness can be firstly determined at its resonant peak, and then the aperture size can be determined at a tradeoff between the field enhancement and the field distribution. The calculation results of the transformed bow-tie apertures indicate that the transformation at tip angle will bring an obvious change to light field distribution. The bow-tie aperture can be directly used as an exit aperture of a very small aperture laser (VSAL) or as an unattached shield, to produce a sub-wavelength light source with high transmission. It is possible to be used in near field super-resolution imaging, high-density optical data storage, nano-photolithograhy and so on.
A near-field optical virtual probe based on the principle of near-field evanescent wave interference can be used in optical data storage, nano-lithography, near-field imaging and optical manipulation etc. The best choice of evanescent wave interference is evanescent Bessel beams that have the characteristics of both propagating Bessel beams and evanescent wave. It is concluded that evanescent Bessel beams is an evanescent wave with the characteristics of diffraction free and radial polarization. These characteristics lead to several advantages in near-field optics: the focus of radially polarized light can be quite smaller than the one of linear polarized light used commonly and diffraction free can bring in constant intensity distribution in a certain range. Meanwhile, based on the concept of conventional apodization, the idea of apodization of evanescent field is proposed to overcome some disadvantages of evanescent Bessel beams, such as the big side lobe and spread of transversal intensity. In this paper, Finite Difference Time Domain (FDTD) method is adopted to simulate the evanescent Bessel beams. Several parameters are considered as variants changeable to get the different simulation results. The better performance of the side lobe suppression and the narrow spot size are discussed. This work may be important to the application of near-field optical virtual probe in the future.
KEYWORDS: Raman spectroscopy, Near field scanning optical microscopy, Near field, Silicon, Spectroscopy, Reflection, Spatial resolution, Atomic force microscopy, Objectives, Microscopes
The combination of scanning near field optical microscopy (SNOM) and Raman spectroscopy provides specific spectra information with nanometer spatial resolution beyond the diffraction limit, which has a wide range of potential applications and can help to understand the interactions between light and matter in nanometer scale. In this paper, a near-field Raman spectroscopy experimental setup has been developed by using an apertureless SNOM system. An Ar+ laser (514nm ) is focused at an angle onto the sample surface. The metallized tip is an Au-layer-coated cantilever of an atomic force microscopy and working in the contact mode. The near field Raman spectra signal can be detected when the tip approached the sample surface. In addition, the apertureless SNOM appears to have greater potential resolution than aperture-type SNOM system. Furthermore, the reflection geometry employed in this experiment allows no need for specific sample preparation, making near field spectrum study a reality for any samples. The reflected near field Raman spectra signal is collected by a microscope objective. Finally, the near field Raman spectra of monocrystalline silicon are presented.
In conventional optical tweezers system a high numerical aperture (NA) objective is employed both to image and to generate a gradient force toward the focus on sample particles, so the system is complex and expensive especially for the multi-optical-tweezers system. We built a novel simple optical trapping system based on a lensed optical fiber probe. This new method offers several other advantages over the conventional optical tweezers. The trapping system we built includes a laser coupling unit, a multi-dimensional probe manipulating unit, a sample nano-positioning unit, and a microscopy imaging unit. Based on the system, a yeast cell is trapped and manipulated on the chamber bottom by the lensed fiber probe, and the optical trapping forces acting on the yeast cell as a function of the offset are measured and discussed in different directions by the static method and the dynamic one respectively with various powers. The results by the two measurement methods coincide with each other, and the detail experimental procedure and the data processing of the two methods are introduced in this paper.
KEYWORDS: Near field, Near field optics, Optical storage, Near field scanning optical microscopy, Solids, Optical recording, Prisms, Refractive index, Objectives, Virtual reality
Near-field optical recording based on solid immersion lens (SIL) system has attracted much attention in the high-density storage in recent years. The recording spot size can be decreased using the SIL effectively. The SIL near-field optical storage has advantages of high density, mass storage capacity and compatibility with many technologies well developed. We have set up a SIL near-field static recording system. The experimental result with recording spot size 200 nm is presented. The influence factors in SIL near-field recording system are also discussed in the paper. Near-field optical virtual probe (NFOVP) is a kind of virtual probe by the evanescence wave interference and aperture diffraction based on SIL. It has a great potential in near-field optical data storage. In this paper, the most important characteristics of the NFOVP has been revealed through numerical simulation. The FWHM of central peak, the size of near-field virtual probe is constant whatever the distance increases in a certain range so that the critical nano-separation control in the SIL near-field data storage system can be relaxed. A realization model of NFOVP based on SIL system for data storage has been proposed and the simulation result based on this model is presented.
We summarize some design tips and design procedures of nanoapertures with strong field enhancement, based on the theoretical calculations and analyses of near-field distributions of unconventional C apertures and bow-tie apertures by a finite-difference time-domain method. A novel L-shaped aperture is proposed and further validates the proposed design rule. As a result, a 15×15-nm full width half maximum spot forms in the light exit plane of the L aperture. Its intensity maximum enhancement reaches a factor of about 568 and the power throughput is bigger than unity. The mechanisms of electromagnetic field enhancement are preliminarily analyzed. This unconventional nanoaperture is likely to be directly used as an exit aperture of very small aperture lasers, or as an unattached shield, to produce a subwavelength light source with high transmission.
KEYWORDS: Near field, Near field optics, Optical storage, Diffraction, Interfaces, Data storage, Solids, Data modeling, Near field scanning optical microscopy, 3D modeling
Near-field optical virtual probe is a kind of virtual probe based on evanescence wave interference and aperture diffraction, which has great potential in near-field optical data storage.
The optical properties of random Sb-SiN films in which Sb nano-particles are randomly dispersed were studied. Results show that the random Sb-SiN films possess high transmittance and low optical absorption. Additionally, some optical nonlinear phenomena of the random Sb-SiN films have been observed. Based on the special optical properties of random Sb-SiN films, they can be applied in many fields, for example, optical storage and optical microscopy. When the random Sb-SiN film was prepared close to a phase-change-recording layer, it decreases the threshold of input power for recording and speeds up the phase transition of recording media, and also improves the resolving power of readout system. On the other hand, while the random Sb-SiN films were deposited on the slide glass used in far-field optical microscopy, it obviously improves the resolving power of optical microscope and reduces the value of resolution limit to less than half of the value calculated by the expression given by Lord Rayleigh.
The aberrations are introduced by a hemisphere solid immersion lens (SIL) with a thickness error or a lateral eccentricity in the SIL optical data-storage system. Numerical computation about these aberrations is presented. We have investigated the influence of these aberrations on the focus spot size, signal intensity, and signal contrast. The simulation results show that a tolerance of the SIL is about ± 20μm in the thickness or in lateral eccentricity.
KEYWORDS: Near field, Near field optics, Objectives, Solids, Optical recording, Optics manufacturing, Near field scanning optical microscopy, Control systems, Microscopes, CCD cameras
Near-field optical recording based on solid immersion lens (SIL) system has attracted great attention in the field of high-density data storage in recent years. The diffraction limited spot size in optical recording and lithography can be decreased by utilizing the SIL. The SIL near-field optical storage has advantages of high density, mass storage capacity and compatibility with many technologies well developed. We have set up a SIL near-field static recording system. The recording medium is placed on a 3-D scanning stage with the scanning range of 70×70×70μm and positioning accuracy of sub-nanometer, which will ensure the rigorous separation control in SIL system and the precision motion of the recording medium. The SIL is mounted on an inverted microscope. The focusing between long working distance objective and SIL can be monitored and observed by the CCD camera and eyes. Readout signal can be collected by a detector. Some experiments have been performed based on the SIL near-field recording system. The attempt of the near-field recording on photochromic medium has been made and the resolution improvement of the SIL has been presented. The influence factors in SIL near-field recording system are also discussed in the paper.
KEYWORDS: Near field scanning optical microscopy, Near field optics, Near field, Optical storage, Optical resolution, Objectives, Nonlinear optics, Diffraction, Solids, Optical properties
Based on theory and method of the near-field optics, optical resolution of near-field scanning optical microscopy (NSOM) is beyond the classical optical diffraction limit and down to tens of nanometer or even less. In this paper, a collection mode NSOM is built to detect and analyze local near-field distribution. The output optical field of a standard 1μm×1μm scale 2D grating has been detected. This NSOM system can also be used to study local near-field distribution of the focused spot of solid immerging lens (SIL) and the result can be directly used to evaluate SIL and compared with the calculation of its theoretical model and as a result, to improve the theoretical model.
KEYWORDS: Near field, Near field optics, Diffraction, Interfaces, Polarization, Optical storage, Finite-difference time-domain method, Near field scanning optical microscopy, Solids, Optical imaging
Near-field optical virtual probe (NFOVP) is a kind of immaterial tip based on evanescence wave interference and nano-aperture diffraction, which has great potential in near-field optical data storage, nano-lithography, near-field optical imaging and spectral detection, near-field optical manipulation and etc. . In this paper, the characteristics of NFOVP have been revealed through numerical simulation by the method of 3-D Finite-Difference Time-Domain (FDTD) and vector diffraction. The simulation results show that the transmission efficiency is higher than that of nanoaperture metal-coated fiber probe widely used in near-field optical systems. The FWHM of central peak, in other words, the size ofnear-field virtual probe is constant whatever the distance increases in a certain range so that the critical nanoseparation control in near-field optical system can be relaxed. A realization model of NFOVP in solid immersion lens system has been proposed. The influences of some factors of NFOVP, such as the shape and size of aperture, polarization and etc. have been analyzed. And the results also show that sidelobe suppression may depend on optimization ofaperture function and incident beams of NFOVP.
KEYWORDS: Near field optics, Optical fibers, Particles, Finite-difference time-domain method, 3D modeling, Near field, Optical spheres, Optical tweezers, Metals, Coating
The technique ofoptical fiber trapping has been successfully used to manipulate small particles, while near field optical tweezers based on the sub-wavelength size fiber tip has been proposed to trap nanometric particles. With some similar physical mechanism and properties they are investigated and analyzed respectively in this paper. Firstly the optical field distributions of uncoated fiber probe with different radii of tip, from several microns down to zero, are calculated and analyzed by 3D finite-difference time-domain (FDTD) method. Then the metal-coated fiber probe is also discussed in the same way. In conclusion, the light from the fiber probe with the radius larger than wavelength is converged at a cometic spot, whatever with or without metal coating. When the radius of metal-coated tip is smaller than halfofwavelength, the evanescent field occurs and decays rapidly. The local field enhancement dominates in the metal-coated probe ifthe radius is smaller.
KEYWORDS: Near field, Near field optics, Metals, Light sources, Optical storage, Finite-difference time-domain method, Semiconductor lasers, Polarization, Electromagnetism, Data storage
Nanometric light source is one ofthe most important elements in near-field optical system. In this paper the nearfield distribution of nano-aperture lasers (NAL) with square and asymmetrical C aperture are characterized by the method of 3D finite-difference time-domain (FDTD). The simulation results theoretically reveal that the output power peak from the asymmetrical NAL is three or four orders of magnitude higher than that from the normal square or round aperture with the comparable light spot size in the near-field region and power throughput is more than unity. The maximum ofthe field enhancement occurs at the C aperture size corresponding to one third ofwavelength. The effects of configuration, aperture dimension, electric field component, polarization and separation in local near field close to the aperture have been investigated theoretically and numerically. The mechanism of electromagnetic field enhancement is also discussed. The asymmetrical NAL with higher throughput may expand the range of applications possible in near-field optics.
KEYWORDS: Plasmons, Near field optics, Transmittance, Near field, Germanium antimony tellurium, Optical switching, Data storage, Thin films, Near field scanning optical microscopy, Scanning electron microscopy
Nonlinear optical transimittance in the Super-RENS (super-resolution near-field structure) [glass/SiN(20nm)/ Sb(15nm) /SiN(20nm)] was investigated using a static transmittance measuring system with a focused laser illumination. The result shows an optical switching property with a strong nonlinear effect. Some SEM(Sanning Electron Microscope) images ofrecording spots in a PC(Phase Change) GeSbTe layer with and without the Super-RENS layers covering on it are presented. The images demonstrate the field enhancement effect due to the Super-RENS layers. The cause of the enhancement is considered as the local plasmon excitation.
KEYWORDS: Near field, Near field optics, Radio propagation, Super resolution, Optical storage, Nonlinear optics, Numerical simulations, Diffraction, Computer simulations, Germanium antimony tellurium
High density optical data storage based on near-field optical super resolution is a new t4echnique that attracts great attention in recent years. Super-resolution near-field structure, glass/SiN/Sb/SiN, a promising structure for near field ultrahigh-density optical storage, has been proposed and investigated since 1998. The recording mark size is a few tens of nanometers, far beyond the diffraction limit of the traditional optics. The mechanism of this Super-RENS including the working principle of the non-linear optical layers and the size reduction of the recording marks has not been clearly understood. In this paper, the electromagnetic propagation in Super-RENS is numerically simulated. The results show that the recording mark size is reduced and the peak intensity increased by the Super-RENS. The mechanisms of the phenomenon is discussed.
Dynamic geometric parameter measurement plays an important role in most industries. Research and development on this technology have attracted great attention. We proposed a laser tracking system for measuring development of laser tracking technology, a laser tracking system consisting of three tracking and measuring stations is described in detail. The three stations track respectively three retro reflectors on the moving target, and measure the position and attitude. We built the mathematical model of measurement and developed the algorithm for processing data. According to the homogeneous coordinate transformation, we deduced the formulae for computing coordinates and attitude under different coordinate systems. Some key techniques of the measuring system are discussed at the end of the paper.
The spatial position of industrial object, such as robot end- effector, is an important geometric parameter whose accuracy determines whether robot can perform accurately. Therefore, we have established a laser tracking and coordinate measuring system with galvanometer scanner for high accuracy, large range, non- contact, and spatial dynamic measurement. In this paper, the laser tracking system and its setup are illuminated at first. Then, the formulae for calculating coordinates are deduced, and the calibration method of the initial distance from tracking mirror to target is presented. After that, two preliminary experiments in different distances are described. One is on CMM; the other is with grating ruler as reference. In the former, the maximum measurement error of coordinates is 70micrometers and the maximum error of length is 35micrometers in the 85x100x100mm3 measurement volume, and in the 1m initial distance. In the later, the maximum error of length is 140micrometers in the range of 480mm, and in the 5m initial distance. At the end of the paper, the error sources are analyzed and simulated.
KEYWORDS: Luminescence, Molecules, Near field scanning optical microscopy, Near field optics, Microscopes, Atomic force microscopy, Image resolution, Near field, Photon counting, Signal detection
The operation principle and configuration of the Scanning Near-field Optical/Atomic Force Microscope (SNOAM) is introduced in the paper. DNA molecules were imaged in AFM mode and in SNOM mode. The topography images and the fluorescence images of single DNA molecule were obtained. The topography image in SNOM mode is of high resolution. The near-field fluorescence image shows the fluorescence distribution of DNA molecules. (lambda) DNA Molecules, in which YOYO-1 was intercalated, were imaged and characterized. For (lambda) DNA with 5 (mu) M YOYO-1, there is variation in the fluorescence intensity of the DNA and ratios of the fluorescence intensity showed almost integers in each region. As the fluorescence intensity correlated with the area of cross section in the DNA topography, it was suggested that YOYO-1 intercalated in the DNA homogeneously. Contrary, the fluorescence intensity of (lambda) DNA with 500 (mu) M YOYO-1 was heterogeneous and did not correlate with the area of topographic cross section. This suggested that YOYO-1 was not intercalated to (lambda) DNA uniformly in the concentration and intercalated partially and cooperatively.
KEYWORDS: Near field scanning optical microscopy, Near field optics, Optical fibers, Fiber lasers, Transmittance, Near field, Photography, Wet etching, Holograms, Holography
As one of the key components in scanning near-field optical microscopes (SNOM), optical fiber probes can be fabricated by use of either laser-heated pulling or chemical etching. For high-resolution near-field imaging, the near-field optical signal is rapidly attenuated as the aperture of probes decreases. It is thus important to fabricate probes optimized for aperture size and optical transmission. We present a two step fabrication method of 50 - 70% reproducibility to obtain probes with high optical transmission efficiency as well as small tip diameters. First, optic fiber probes with the transitional taper in hyperbolic or parabolic shape are produced by use of the simple home-made device for heating- pulling. Then, a rapid chemical etching with 40% buffered hydrofluoric acid is used to sharpen the tip while keeping the taper shape and the conic angle unchanged. The method renders us to achieve probes with tip diameters in the range of 20 nm - 200 nm and the tape angle near the tip apex in the range of 20 degree(s) - 60 degree(s). Particularly, the length of the non- propagating evanescent wave modes region decreases greatly to tens of micrometers or even less. In order to test the achieved probes, we give the photon tunneling decay curve and scanning near-field optical image of holographic grating by use of PSTM mode and collection-mode SNOM, respectively. In addition, an approach curve of shear force with hyperbolic probe is shown to verify its applicability to sample-tip distance regulation on basis of the principle of shear-force.
KEYWORDS: Near field, Refractive index, Fiber optics, Near field scanning optical microscopy, Metals, Wave propagation, Polarization, Near field optics, Finite-difference time-domain method, Light wave propagation
In this paper near-field distributions of nanometric apertures, the uncoated and metal-coated fiber-optic probes used in near-field scanning optical microscope are characterized by the method of finite-difference time- domain. Moreover, to give a clear view of the influence of parameters, say, the taper angle ((alpha) ), the aperture diameter (d), the refractive index of the fiber-optic (n) and the sample (ns), the tip-sample separation (z), on the throughput of metal-coated fiber-optic probes, we investigated it in detail.
The main methods for measuring geometric parameters used to be static or quasi-static. At present, former static measurement methods with sliding guide have met with great difficulty when measuring the outline and profile of large-scale workpiece or coordinates of objects moving in large dimension. Thus we established the laser tracking system for high precision, large range, non-contact, dynamic measurement. Laser tracking system involves in interdisciplinary knowledge and it can be made up into a new type of computer integral system with both measuring and controlling capacity. With common static coordinate measurement system, such as CMM, the probe must move along the three orthogonal guides equipped with standard rulers, while the laser tracking system has no such objective reference coordinate system. So we put forward the notion of 'Virtual Coordinate System,' that means during the measurement, the coordinate frame is not fixed. On the primary stage of our research, we established practical system for 2D moving target measurement in real-time. In order to measure the coordinate of the target, three tracking stations are used, which only measure length changes between the target and stations each, with no angles are measured. By solving non- linear least-square equations, the target and the tracking stations' coordinate can be attained respectively. We also present the optical design and the tracking controlling system based on the PID controlling principle. At the end of this paper, we will give the experiment result of the system.
Laser tracking and measuring system is made for real-time measurement of dynamic target in industry field and it can be made up into computer integral system with both measuring and controlling capacity. The system has no objective reference coordinate system, during the measurement, its coordinate frame is not fixed, so we call this coordinate system as Virtual Coordinate System. Laser tracking system involves interdisciplinary knowledge, such as laser dynamic aiming technique, laser interferometry, optical system and precision mechanism design, motor controller design and modern numerical computation. This paper mainly focuses on the otpical system analysis and design. The system, which can track and measure the dynamic target, uses the dual- frequency laser interferometer as the light source and length-measured sensor simultaneously. The interferometer produces linear-polarized orthogonal beam with two different frequencies. When the beam passes through the optical system, its polarization and amplitude will be both changed. This paper presents vector analysis method for the optical tracking systems and analyzes the polarization effect of the optical system on the light beam incident in any direction by Jones matrix analysis. On the basis of analytical and experimental results, the optical scheme is optimized in order to improve the tracking and measuring performance of the whole system.
KEYWORDS: Near field scanning optical microscopy, Ferroelectric materials, Optical microscopy, Electrodes, Liquids, Near field optics, Signal detection, Metals, Ceramics, Diffraction
In this paper a novel method for tip-sample distance regulation based on shear-force is presented. A semicircular piezo-electric ceramic plate is used as the excitation as well as detection element, the electrode of which is divided into three segments. The first segment is excited by a generator and the second one is used to fix the fiber tip. The induced voltage on the third segment is used to detect the tip-sample distance. The approach curves show that it is very sensitive and the tip-sample distance can be regulated below 5 nm. Experimental results indicate that when the sample is covered with liquid the approach curve is different from that in the air. In addition, during experiments we found that at some resonant frequency the approach curve is different from the conventional shape. The phenomenon, if proved reliable, can be used to realize automatic and rapid tip-sample approach as well as small-scale distance regulation.
A four-segmented piezoelectric tube performs XYZ spatial scanning in a SPM system. The measurement of characteristics including scanning range, accuracy, linearity and the lowest resonant frequency are essential to obtain a reliable image and get information about the scanning velocity. An optical fiber laser interferometer capable of vibration measurement is used to characterize the scanning tube with the inner diameter of 6mm, thickness 1mm and length 25mm is measured. We find that the lowest resonant frequency is much lower than the calculated result. The low resonant frequency will limit the scanning velocity and influence the quality of the obtained image greatly. In addition, the non-linearity curve can be obtained by driving the scanning tube with a triangle wave slowly. The measurement is easy, quick and continuous. In addition, we measure the non-linearity statically by inductive micrometer as well. The two results are compared. The result shows that there is difference between them.
The main methods for measuring geometric parameters are used to be static or quasi-static measurement. Recently, however, dynamic geometric parameters measurement has been becoming increasingly important and turning into a new field in metrology. The laser tracking system for measuring dynamic geometric parameters of moving targets employs laser dynamic aiming technique, laser interferometry and control technique of precision instruments. The moving target is tracked and its geometric parameters are measured in real time. The measurement range is one to ten meters and the accuracy is fifty microns per meter. It is a novel computer integral system with both measuring and controlling capacity. This paper present the characteristic and concept of dynamic geometric parameters measurements and puts forward the cardinal measuring principles and methods of the laser tracking system. This paper also gives a more detailed discussion about the key techniques for this system, which are different from the static measurement, such as the self- calibration principle, the redundancy design principle, the fault-tolerant design principle, the virtual coordinate system establishment principle. We will also discuss the developing trend of laser tracking system for measuring dynamic geometric parameters at the end of the paper.
A four-segment scanning PZT tube is characterized using a laser vibration measurement system. Several periods of quasi-decay mechanical oscillation are observed in the experiments when the scanning tube is driven by series of step signals. The oscillation frequency is much lower than the lowest resonant frequency calculated base on the reported formula. The mechanism of the oscillation is analyzed. The possible reasons include mechanical inertial or damping, driving power supply impedance properties and the base vibration are discussed. The low resonant frequency of the scanning tube may be the result of its own complicated boundary conditions based on the experimental result of amplitude and frequency properties although there is a considerable difference between theoretical and experimental results. Some possible approaches to reduce or eliminate oscillation are proposed.
The micro- and nano-science and technology has been developing in recent years. Employing the state-of-the-art manufacturing technology the sizes of microstructures are generally in micrometer scale or even in nanometer scale. This paper describes several vibration measurements in microstructure investigations with a laser vibrometer. The microstructures are Si lever, cantilever and cantilever probe in the AFM. Dynamic characteristics of optical fiber building the distance regulation in the NSOM and of Si membrane excited with laser beam in single direction and double opposite direction in thermal sensors were investigated. The vibration curves and experimental results are given. Further possible vibration measurements in micromachine and nano-science and technology is discussed.
Some problems in a near-field scanning optical microscope (NSOM) system for observing biological living specimens is discussed. The NSOM system works based on the principle of nano-optics and near-field optics. Propagating characteristics of evanescent wave field, the effects of absorption, polarization changes, fluorescence, optical density, refractive index, luminescence and incident angle are analyzed. Methods eliminating pseudo-image in specimens are proposed. NSOM will be employed to conduct investigation of single molecule of living biological specimen and make precision metrology researches in nanometer scale.
A laser Doppler velocimeter (LDV) based on laser heterodyne interferometry is described in this paper and has been used to measure the dynamic characteristics of disks. The digital linear phase low pass filter and differential filter are designed and used in the data processing system. The measurement results on the dynamic characteristics, velocity, acceleration and runout in axial direction of the hard disk at 3600 rpm are given.
The paper discusses some optical methods of measuring the profile of disk non-contacting. Grazing incident interferometer, Color schieren, and Moire deflectometer. Especially in the paper a new measuring method and instrument is introduced which is a pointwise instrument with an optical probe. It can measure a global and local profile of a disk in tangential and radial direction at the same time, without sacrificing the measurement accuracy. The resolution of the probe is 0.3 nm, the instrument accuracy better than 0.04 micrometers , the dynamic range larger than 5 mm.
An optical heterodyne system for the measurement of profile and roughness has been developed. Several improved techniques are employed. The optical system was designed with entire common path. The effect of sample vibration and the thermal drift could be eliminated. A modified objective was used to perform respectively the measurement beam and the reference beam. The detected signals were processed with phase comparison technique to give a high accuracy. The optical system can be developed to an accessory of the Zeeman laser interferometers.
The paper introduces a new method to measure the flatness of the disk
with the laser heterodyne interferometer. Its most important advantage is
that it can measure the large and intermediate scale disk profile at the
same time, without sacrificing the measurement accuracy. The resolution
of the interferometer is 0.3 nm, the accuracy better than 0.04 jim, the
dynamic range larger than 5 mm. Otherwise the interferometer can nieasure
the disk global and local profile in tangential and radial direction.
A magnetic disk surface profilometer employing point to point scanning method is presented. The profilometer can be used to measure flatness, global and local profile in circumference, straightness and local fine profile in radius. The theoretical resolution is 0.3 urn, accuracy of the sensor is better than 0.04 ni, dynamic range is larger than 10 mm.
Measurement of temperature distributions in D,0 in the cold fusion device BUNCO with a holographic interferometer and with a thermocouple is presented in this paper.
A method for non-contact on-line measuring large shaft diaseter using laser beas scanning technique is presented in this paper. Diaaeter froa 500 to 2000 s can be Measured by the aethod over large seasuring range resolution is 0. 005 ii accuracy of variation over 700 0. 02 s. 1 .
Many Methods have been developed to .easure displace.ent with high accuracy, for
exap1e, with a dual frequency laser interferometer (AC interferometer) and an classic
interferoseter (DC interferoeter) which use a stabilized laser and fringe counter, and
an AC interfero.eter has ore advantage over the DC one.
An AC interfero.eter with a Zee.an laser can get a high resolution, in the order of
nanoMeters, but its resolution extension liRited by nonlinear relation between phase and
displace.ent which caused by the two-frequency coRponents in interferoaeter[1]. Because
the fundaaental length scale of the interferometer is the wavelength of the light source
in the air. The accuracy of an interferoeter is li.ited by the operating envireaent,
teRperature, husidity, pressure, etc. because the aiRs of interferoseters expose in the
air. A high resolution optical fiber heterodyne interfermeter is described in the paper.
An heterodyne interferoaeter is constructed with a sodulated laser diode (LD) in a Michelson interferoaeter. Phase drift of beat frequency with teiperature and its affection aechanis is discussed and a method elisinating the affection aentioned above is proposed. 1 . OPTICAL HETERODYNE INTERFEROMETER Optical frequency of laser diode can be linearly aodulated by an injection current. An optical heterodyne interferoseter is constructed with a modulated laser diode in a Michelson interferoseter. If a difference exists between two arms in the interferometer a optical beat frequency phenoaenon will be forRed. The beatfrequency signal can be detected with a photoelectric device. The output signal can be described by the following equation: 1g10[1+cos(2xfbt+t)J (1) and fb is given by fb 6f''8Lf. I C (2) Where f is the aaxiRua optical frequency variation value of wxiulated laser fb the beat frequency value fa the odulated signal frequency L the optical path difference between two aras in the interferoaeter C optical wave speed. 2. VARIATION OF BEAT FREQUENCY PHASE WITh TEMPERATURE It is well known that the optical frequency of a laser diode is affected by the tesperature (in the equation (1)) ay be changed with the variation of central wavelength of . odulated optical frequency. t aay be expressed in the for. : Li A242Ai t 2ir( ) (3) AiA2 The plus and ainus . arks in the equation above are corresponding to the upward
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