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Displacement measurement in real time using the attenuated total reflection technique
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A simple displacement measurement based on the attenuated total reflection technique is proposed and experimentally demonstrated. By analyzing the fringe shift of the reflective pattern recorded on a CCD camera, a slight displacement, which corresponds to a change in the waveguide thickness, can be determined in real time with adequate accuracy. The measurement range of this method is about 240 μm, and its accuracy can reach 0.05 μm. © 2004 American Institute of Physics.
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... 2 The methods can be classified into those based on autocollimators, 3-8 interferometers, [9][10][11][12][13][14][15] total-internal-reflection effect, [16][17][18][19][20] fringe analysis, 21 and some other special techniques. [22][23][24][25][26][27][28][29] For autocollimators and interferometers, they exert measurements by obtaining the phase difference of two interference signals. The bulky volume makes them unsuitable for applications in some space-limited areas. ...
Accurate rotation sensors are highly demanded in both industrial applications and academic research. We experimentally demonstrate an angle measurement method based on an alkali-metal vapor cell. In our experiment, the rotation signal is converted to the polarization of the laser beam passing through a quarter-wave plate coaxially mounted on a detected object. The polarization is then measured by monitoring the transmission of the laser beam through the vapor cell. Using this method, we demonstrate an angle measurement sensitivity of 2×10−5°/Hz without a magnetic shield. The results shown in this paper provide a prototype of the angle measurement with high accuracy, compactness, and low cost.
... For surface Plasmon resonance is sensitive to the physics quantities such as small change of angel [2]. Displacement [3], humidity [4], and temperature [5]. By measuring the refractive index(RI) by the sensor, we can monitor the concentration of the analyte of the solution, which reflect the process of chemical reaction. ...
A surface plasmon resonance (SPR) bio-sensing system has been developed. The system is based on polarization interferometry and angel modulation. In this paper, we apply it in the biological detection. We use the DNA fragment of Escherichia coli (Bacterial 16S rDNA universal primer) as bioprobe and . The process that analyte attach with the bioprobe, and coli DNA as analyte, get a resolution about 2.7× 10-6RI and 0.18nM/L in coli DNA detection.
This book provides a comprehensive description of various slab waveguide structures ranged from graded-index waveguide to symmetrical metal-cladding waveguide. In this book, the transfer Matrix method is developed and applied to analyze the simplest case and the complex generalizations. A novel symmetrical metal-cladding waveguide structure is proposed and systematically investigated for several issues of interest, such as biochemical sensing, Goos-Hänchen shift and the slow light effect, etc. Besides, this book summarizes the authors’ research works on waveguides over the last decade. The readers who are familiar with basic optics theory may find this book easy to read and rather inspiring.
This chapter introduces several basic optical devices based on the attenuated total reflection, including tunable filter, optical sensors, and electro-optical devices. We mainly focus on the description of optical sensors performance. It is found that the bigger the portion of power that propagates in the sample, the higher the sensitivity will be. Moreover, the sensors based on the GH shift are immune to the power fluctuation in the light source since the GH shift is position encoded. Finally, our experiments to explore the magneto-optical modulation and all-optical modulation in the ferrofluid-filled SMCW are given. The results are contributed to the competition between the optical trapping effect and the Soret effect.
The transfer matrix method used in thin-film optics is extremely useful when applied to analyze the propagation characteristics of electromagnetic waves in planar multilayer optical waveguides. This chapter aims to extend the transfer matrix method to treat the bound modes of the graded-index waveguide. Beginning with a brief introduction of the transfer matrix, we derived the eigenvalue equations and studied the multilayer optical waveguides. Different from the widely used WKB approximation, the transfer matrix obtained some important but different conclusions when applied to the graded-index waveguide, such as the exact phase shift at the classical turning points.
SiO2/TiO2/methylcellulose composite materials processed by the sol-gel technique were studied for optical waveguide applications. With the help of methylcellulose, an organic binder, SiO2/TiO2/methylcellulose hybrid thick films were prepared by a single spin-coating processes. After annealing at 70 Celsius degree for an hour, 2.5-?m crack-free and dense organic--inorganic hybrid optical films with a refractive index of 1.537 were achieved. Optical losses of plane waveguide made up of those films and ordinary slide glass substrate are around 0.3 dB/cm at 650 nm. Scanning electronmicroscopy (SEM) and UV-visible spectroscopy (UV-VIS), have been used to characterize the thick films.
The synthesis by pulsed laser deposition technique of zinc oxide thin films suitable for gas sensing applications is herein reported. The ZnO targets were irradiated by an UV KrF* (λ=248nm, τFWHM∼7ns) excimer laser source, operated at 2.8J/cm2 incident fluence value, whilst the substrates consisted of SiO2(001) wafers heated at 150°C during the thin films growth process. The experiments were performed in an oxygen dynamic pressure of 10Pa. Structural and optical properties of the thin films were investigated. The obtained results have demonstrated that the films are c-axis oriented. Their average transmission in the visible-infrared spectral region was found to be about 85%. The equivalent refractive indexes and extinction coefficients were very close to those of the tabulated reference values. Doping with 0.5% Au and coating with 100 pulses of Au clusters caused but a very slight decrease (with a few percent) of both transmission and refractive index values. The coatings with the most appropriate optical properties as waveguides have been selected and their behavior was tested for butane sensing.
Instead of analyzing the fringe shift that was recently developed by us to detect slight displacement, an alternative approach by monitoring changes in the intensity of the light reflected from a variable-air-gap optical waveguide is presented in this work. Owing to the sensitive feature of the ultrahigh-order modes, a 1.7 nm resolution of displacement measurement is demonstrated without any complicated optical interference system and servotechniques.
Mesoporous siliceous SBA-15 functionalized by γ-aminopropyltrimethoxysilane (APTMS) was used to immobilize Au and Au–In nanoparticles via the amino groups. The uniformly sized Au and Au–In spherical particles of around 2nm were homogeneously dispersed on the mesopore walls of SBA-15. In liquid phase hydrogenation of crotonaldehyde to crotyl alcohol, on the optimal Au5.0In0.75/APTMS-SBA-15 catalyst, the initial selectivity amounts to 78%, and the maximum yield reaches 71%. The high selectivity originates from the suppression of the hydrogenation of the CO bond being lower than that of the CC bond after the incorporation of In. Furthermore, the catalyst can be conveniently recovered for reuse without losing its selectivity. In light of a series of spectroscopic studies, the superior catalytic performance of the Au5.0In0.75/APTMS-SBA-15 catalyst is tentatively attributed to the electron-donating effects of APTMS and In alloying with Au, favoring more the binding and hydrogenation of the CO bond in crotonaldehyde.
We report on new features of nanostructured coatings used in trace gas detection applications based on the modification of
optical parameters. We review the general physical principles underlying the operation of optical detectors and introduce
the basic systems used in trace gas recognition. Pd-doped SnO2 thin films were pulsed laser deposited on Si (100) and quartz substrates in 10 Pa O2 at different substrate temperatures. Coatings on Si were investigated by scanning electron microscopy and atomic force microscopy
to determine their surface morphology and by grazing incidence X-ray diffraction for films structure. Twin films deposited
on quartz were investigated using the m-line technique to monitor the variation of optical properties when exposed to butane diluted in N2 down to 100 ppm concentration. The acquired expertise was used to design a miniaturized system which was tried in real conditions.
A new method of exciting nonradiative surface plasma waves (SPW) on smooth surfaces, causing also a new phenomena in total reflexion, is described. Since the phase velocity of the SPW at a metal-vacuum surface is smaller than the velocity of light in vacuum, these waves cannot be excited by light striking the surface, provided that this is perfectly smooth.However, if a prism is brought near to the metal vacuum-interface, the SPW can be excited optically by the evanescent wave present in total reflection. The excitation is seen as a strong decrease in reflection for the transverse magnetic light and for a special angle of incidence. The method allows of an accurate evaluation of the dispersion of these waves. The experimental results on a silver-vacuum surface are compared with the theory of metal optics and are found to agree within the errors of the optical constants.
A simple 3-D displacement measurement method using a photorefractive interferometer is proposed and experimentally demonstrated. A photorefractive crystal attached to the sample under test is used to record an original spherical wave that provides a shifted reconstructed wave after displacement. The shifted wave interferes with direct wave to form an interferogram. By analyzing the fringe pattern the in-place and out-of-place displacements can be determined at the same time. This method works in real-time and is easy to operate with adequate accuracy comparable with or even better than that of other techniques.
The purpose of this study is to develop a more efficient measuring method of 3D edge profile with high accuracy for free-form surface including die and mould model shapes. In this paper, we propose a new method of 3D edge profile measurement by means of optical ring image sensor. Optical ring image sensor has more advantages than the others because it detects as not a light spot but a ring image of the reflected light from a target point. We note that the intensity of optical ring image changes in the edge. The differences between the intensities of ring images in the plane and the edge are represented by cross correlation coefficient, which is used as measuring parameter to detect the 3D edge profile of a master model.We propose the two-step measurement for detecting the edge profile, first the edge area for re-measuring which may include the edges extracted by rough measurement, and second the measuring path of the sensor is decided by the shape of edge areas so that it may cross the edges certainly. Finally, we estimate the edge positions, namely the edge profile using the cross correlation coefficients is obtained by fine measurement along the measuring sensor paths.
A speckle correlation technique is proposed for the measurement of small object tilt. Theoretical analysis is formulated for a general case of object tilt. Simulation and experimental studies are performed to verify the outcome of theoretical predictions and accuracy in measurement. Sensitivity of tilt measurement is studied and quantified from observations made from object position in various longitudinal planes. (C) 1998 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(98)01811-X].
The surface plasma wave (SPW) technique for determining the frequency-dependent dielectric constant epsilon(omega) and the thickness d of a metal film without a present expression for epsilon(omega) is discussed. It is shown that two sets of solutions can be derived from the resonant excitation of the SPW at a given frequency. Solutions at another frequency are required to select the correct sets for epsilon(omega) and d (those with the same d for both frequencies).
For in situ measurements of local electrical conductivity of well-defined crystal surfaces in ultrahigh vacuum, we have developed two kinds of microscopic four-point probe methods. One is a ‘four-tip STM prober’, in which independently driven four tips of scanning tunneling microscope (STM) are used for four-point probe conductivity measurements. The probe spacing can be changed from 500 nm to 1 mm. The other one is monolithic micro-four-point probes, fabricated on silicon chips, whose probe spacing is fixed around several μm. These probes were installed in scanning-electron-microscopy/electron-diffraction chambers, in which the structures of sample surfaces and probe positions were in situ observed. The probes can be positioned precisely on aimed areas on the sample with aid of piezo-actuators. With these machines, the surface sensitivity in conductivity measurements has been greatly enhanced compared with macroscopic four-point probe method. Then the conduction through the topmost atomic layers (surface-state conductivity) and influence of atomic steps upon conductivity could be directly measured. The STM prober is mainly described here.
A method is given to determine accurately the optical constants and the thickness of thin films when the real and the imaginary part of the dielectric constants obey the condition ɛ r <- 1, ɛ i ¦ɛ r ¦. The method makes use of the possibility to excite surface plasma waves with the help of the inhomogeneous light wave obtained by total reflexion. The accuracy of the method is pointed out. As an example the optical constants of silver foils in the wavelength interval 4000 to 6000 Å are determined.
We report theory and experiment on modes of propagating light waves in deposited semiconductor films. The modes are excited by a novel prism‐film coupler which is also used for the measurement of their phase velocities. Up to 50% of the incident laser energy has been fed into a single mode of propagation. The positions and linewidths of the modes, the wave intensity inside the film, and a dramatic view of the mode spectrum displayed by the scattered light are discussed in detail.
The present work describes the use of a photorefractive correlator in the measurement of in-plane displacement. A correlation technique has been proposed and demonstrated for precise displacement measurement by recording objective speckles. Speckle interference patterns are generated in situ using a converging beam illumination and two-beam coupling recording geometry in a photorefractive barium titanate crystal. Intermediate digital interfacing through an electrically addressed spatial light modulator enables one to introduce digital processing techniques (viz., thresholding) for improving the fringe contrast resulting in a better quality of correlation output required for measurement accuracy and reliability. This also increases the range of displacement measurement. In-plane object displacement being proportional to the separation between the correlation peaks, a measure of it gives the magnitude of object displacement. Both simulation and experimental studies have been performed on double as well as multiple exposure speckle interference patterns. The effect of threshold binarization on speckle correlation has also been studied. The method promises high degree of accuracy and increased range for displacement measurement in real-time.