The paper presents our progress in using a THz -TDS system for spectral characterization of some organic substances. We try to develop a data base for substances from different domain that include in their category materials having a common characteristic: they are dangerous or they are even forbidden in their category of utilization. We have developed procedures for measuring the absorption spectra in quasi same conditions for all substances. Like this we have record absorption spectra for: food additives (azoic-dyes and fragrance), pesticides (insecticides, fungicides, herbicides) and some alcoholic polar substances (methanol, ethanol) etc. We have demonstrated that our measurements technology can be used not only for recording the spectra of the organic samples, but we can discriminate between different levels of concentration of the substances or even we detect the forbidden substances in an organic material.
In this paper we report spectral measurements of some relatively common substances but from the hazardous category (possibly to be used like explosives or their manipulation is dangerous) in view to create a database with spectra of such substances. THz transmission spectra of some pure materials and mixed ones are also introduced. The measurements were performed using a Time-Domain system that work in the range of 0.2-4.5 THz. We develop our algorithm to obtain maximum information from the measurement and to minimize the errors.
We developed a measuring technology using a TDS-THz system to construct hyperspectral images of some objects, including hazardous materials. “T-rays” (the THz spectral domain of the light) have a growing importance in security and imagistic domain. Due to their property of penetrating through dielectric objects, and using non-ionizing radiations, the THz systems have become a standard for “hot-places” (airports, train stations etc.). The hyperspectral images are 3D images having 2D spatial dimension and one spectral dimension. In this way, we obtain simultaneously information about the form of the object and its molecular composition. For discriminating between substances, we must first build a database of spectra for hazardous and dangerous substances. We experiment our system on some items (among them a firecracker, a cigarette and a metal collar) and we tried to discriminate between them using the database of spectra.
The paper present our first steps to realize a hyperspectral imaging system. Preliminary experiments in the domain have as purpose to test the capability of a monochromator with a 2D linear CCD camera, to create hyperspectral images. Using a Sciencetech 9055 model monochromator with a Hamamatsu CCD, we have analyzed an array of three LEDs of various colors, obtaining 1D hyperspectral images.
Although nowadays spectrometers reached a high level of performance, output signals are often weak and traditional slit spectrometers still confronts the problem of poor optical throughput, minimizing their efficiency in low light setup conditions. In order to overcome these issues, Hadamard Spectroscopy (HS) was implemented in a conventional Ebert Fastie type of spectrometer setup, by substituting the exit slit with a digital micro-mirror device (DMD) who acts like a coded aperture. The theory behind HS and the functionality of the DMD are presented. The improvements brought using HS are enlightened by means of a spectrometric experiment and higher SNR spectrum is acquired. Comparative experiments were conducted in order to emphasize the SNR differences between HS and scanning slit method. Results provide a SNR gain of 3.35 favoring HS. One can conclude the HS method effectiveness to be a great asset for low light spectrometric experiments.
A simple way to make physical encoding of data is to use some common Fourier optics tools, like lenses and some more sophisticated ones like a digital matrix detector (CCD, Charged Coupled Devices), as in Fig. 1. Except now the encoding and the compacting of the data is not made using Hadamard transform but a Fourier transform, which has less compacting power. There is however the big advantage of physically encrypting the data instead of manually or digitally doing the computation. The input data may be anything, a note, a picture, a diagram, anything at all. It may come at a moment notice and does not require any special preparation on the part of the operator. One can accomplish real-time encoding. It may require, however that the message data to be made available in a specific format, independent of the contents of the message. For instance it may have to be inscribed on a transparency and to have certain dimensions.
Radius, roundness and roughness, the three R are the necessary parameters to characterize ball bearings. Roundness is one of the most important geometric forms expected from circular features. Most traditional R3 measuring instruments are stylus type, including the coordinate measuring machines (CMMs). The accuracy requirements for roundness measurements range from a few 0.1 μm for work pieces down to below 10 nm for roundness standards such as precision spheres. White light interferometer is a suitable noncontact method for height profile measurement of objects able to furnish such values. White light interferometer (WLI) produced by Ambios Xi-100 was used to measure radius, roundness and roughness of steel ball bearings. Radius is calculated from the Newton rings easily observed in the interferometer, roundness is observed by limiting the height surface profile between two inner and exterior circles and roughness is RMS value for the best fit line to the ball profile. All the values can be easily obtained from the .txt files produced by the instrument software.
In this paper we are analyzing the coupling between laser radiation and surface in order to set the optimum
work conditions to obtain nanoparticles by laser ablation in liquids (LAL). In this idea we have studied the
effects induced with a 355 nm wavelength Nd:YAG pulsed laser on an aluminum target situated in distilled
water with non contact profilometry (WLI Xi-100) and by optical microscopy (Carl Zeiss microscope). We
have measured, analyzed and intercompared the characteristics of the formed craters (diameter, depth and
shape) on the aluminum target as a function of the laser radiation parameters (incident fluence, number of
Azo-polymeric materials present in the last decade a great interest due to their applications. Our materials are based on polysiloxanic chains, modified with different azo-benzenic groups. This new class of hybrid polymer (organic/inorganic) gives a large potential of applications in biology, chemistry, sensors, microelectronics etc.
Due to photo-chromic properties of the azo-polymers it is possible to apply two kinds of techniques for surface relief
gratings (SRG) generation, necessary for using the polymers in enumerated applications: continuous or pulsed light
irradiation. Our work was focused on SRG generation on azo-polymers by pulsed light irradiation, with a Lloyd
interferometric set-up. The resulting structures were analyzed, from optical point of view, by three methods: white light interferometry (WLI), optical microscopy and diffraction efficiency. All determination has been done in correlations with the irradiation parameters: fluence and number of pulses. We can say that the pulsed radiation interferometric patterning of azo-polysiloxanes is an efficacy and controllable technology to obtain surface relief gratings very necessary for the biological applications (cell culture) and optical methods analyses are useful for rapid determinations.
Aluminium nanoparticles were produced by pulsed laser ablation of a sample of pure aluminium situated in distilled
water. This technique provides the possibility to generate a large variety of nanoparticles that are free of both surfaceactive
substances and counter-ions The sample was irradiated by the focused output of the third harmonics of pulsed
nanosecond Nd : YAG laser operating at 10 Hz frequency. The typical thickness of the liquid above the target was 10
mm. In order to select the most efficient material removal conditions the irradiation print on the ablated surface was
analyzed as a function of the irradiation parameters (incident laser fluence, irradiation pulses number or irradiation
time) with optical microscopy and white light interferometry. The presence of the ablated aluminium nanoparticles in
the liquid was evidenced by SEM. For SEM measurement, one drop of solution containing Al nanoparticles was placed
on a gold coated silicon substrate and dried. The minimum diameter of nanoparticles estimated by SEM was under 100
nm. The SEM results show also clusters of spherical particles together with well-defined singles. In order to improve
the quantity of the ablated material the irradiation cell was mounted on a computer-driven X-Y stage and translated
during laser exposure.
A laser interferometer, a vision system, and 1-D precision translation stage are used to develop a high precision
measuring station with a working range of 12 mm. The object inspected by the laser-and-vision system is moved using a
linear translation stage (LUMINOS INDUSTRIES I1000 - 1-Axis Stage) so that the camera can take images of the
feature points of the object at two (or more) different positions. Meanwhile, the displacement of the table is measured
using a laser interferometer. Putting these two feature points successively in focus the distance between them can be
evaluated and adding the displacement measured by the laser interferometer, the real distance between these two feature
points is obtained. The developed 1-D laser-and-vision measuring system is used to measure the geometric size (pitch) of
grating type linear encoders or industrial line scales. Software counts automatically the number of lines and the laser
interferometer produces the corresponding length. For dial instruments the vision machine observes the coincidence of
the moving needle with divisions representing (sub) units of length. The displacements measured by laser interferometer
are compared with dial indicator and the measuring errors are observed.
UV laser beam interaction with painting layers in case of aged mock-ups was investigated and ablation and cleaning
thresholds were estimated as a function of each layer and sub-layer composition. Ablation depth measurements as a
function of incident laser intensities and subsequent irradiation pulse number was measured with white light
interferometry (WLI) and profilometric methods, demonstrating a selectivity of the removal of painting layers from submicrometric
domain to micrometric domain as a function of surface cleaning needs. The laser cleaning station was
designed and developed after careful evaluation of the irradiation conditions proper to the removal of painting layers. A
Q-switched Nd:Yag laser radiation is delivered to the artwork through a mirror system consisting in an articulated arm
and a laser head. A complete control of the incident laser parameters was envisaged with the laser remote control
interface. The system also comprises diagnosis and monitoring tools for the remote control of the cleaning operation.
The prototype is controlled by an integrated interface based on a user-friendly software to perform the available
operations (e.g. laser cleaning, LIBS, colorimetry, live color monitoring, multispectral analysis, database management).
The user interface is also used to start the treatment of a new work, to review or continue a previously started work.
Semiconductor quantum dots are nanometer-sized crystals with unique photochemical and photophysical
properties that are not available from either isolated molecules or bulk solids. These nanocrystals absorb light over a very
broad spectral range as compared to molecular fluorophores which have very narrow excitation spectra. High-quality
QDs are proper to be use in different biological and medical applications (as fluorescent labels, the cancer treatment and
the drug delivery). In this article, we discuss Fourier transform visible spectroscopy of commercial quantum dots. We
reveal that QDs produced by Evident Technologies when are enlightened by laser or luminescent diode light provides a
spectral shift of their fluorescence spectra correlated to exciting emission wavelengths, as shown by the ARCspectroNIR
Fourier Transform Spectrometer. In the final part of this paper we show an important biological application of CdSe/ZnS
core-shell ODs as microbial labeling both for pure cultures of cyanobacteria (Synechocystis PCC 6803) and for mixed
cultures of phototrophic and heterotrophic microorganisms.
The reorganization processes at submicron level of the polymeric materials have been investigated because of
their applications in optoelectronics and bio-science. We have obtained surface relief modulation in single step
processing on the photo resist and polysiloxane films. But for technical applications the time evolution and
stability of the induced surface structure is an important parameter and is a problem to be discussed. In case of
single step surface relief formation on polymeric materials the process is connected with the photochromic
behavior of the materials. As it is known the UV light induced effects on the material structure are reversible
under the action of visible light, but with different speeds. In this report is analyzed the time evolution of the
surface modulation obtained under the action of the UV light for azopolymers with different structures.
In this paper, a small scale laboratory strainmeter for measuring relative strains is presented. The instrument is a high resolution homodyne interferometer with polarizing optics and special designed electronics for analyzing the output signal of the interferometer. Resolution of the order of λ/8 is obtained in the first instance, with the possibility of improvement by electronic means. Measurement range could vary from microns in the case of earth strains to meters in the case of industrial applications.
Stationary Fizeau fringes, phase shift interferometric fringes, fringes obtained in Murty lateral shear interferometry, vibration interference pattern as seen by digital speckle pattern interferometer all are digitally captured in specific interferometer set- ups. IntelliWave software produced by Engineering Synthesis Design, Inc. (ESDI) is used to process the fringe patterns. For all these fringe patterns the physical principle and set up for obtaining them are described. This could be a resume for student and young researcher guiding in experimental interferometry.
Precise three-dimensional (3D) information is demanded by many new industries such as: semiconductor, photonics, MEMS, communications, microprocessing etc. [1, 2]. The problem is to select the proper measurement methods for material characteristics in the measurement field, from the point of view of the measurement accuracy and errors that can appear [1, 4, 3, 5]. There are several optical 3D measurements approaches, e.g.: triangulation, grating projection with phase shift, moiré with phase shift, confocal and (white light) interferometry (WLI) [2, 3]. They can measures: surface profile, roughness, step height, microstructure, and other surface parameters. The white light interferometers allows generally surface profiling with high accuracy with no phase ambiguity errors, making them more suitable for profiling stepped or discontinuous surfaces. WLI technique to determine the thickness of thin coating on reflective materials is very effective. One of the first techniques to utilize the short coherence of the white light source was the scanning interference microscope. There are on the market a variety of scanning white light interferometers. Measurement calibration is done using the short coherence feature of white light. Some of the presented applications in nanometrology are thin films thickness measurements of: carbons films on glass, metallic films on Silicon, ablated small holes diameter, and profiles of micro / nanostructure.
A laser strainmeter for in-situ monitoring of an important actively seismic area of Europe, namely Vrancea region in
Romania is proposed. Six groups from four different countries (Romania, Czech Republic, Italy and Greece) with
various areas of expertise (e.g. geophysics, lasers, optics, interferometry, and mechanics) are involved in order to sustain
the complexity of the project. This paper presents some preliminary laboratory experiments related to measuring relative
displacements with a stable interferometer. Displacements of the order of tens to hundreds of nanometers (80 to 285 nm)
were measured with uncertainty of ±1 nm. A computer algorithm was used to process the interferograms.
In this paper we describe a traceable to the meter standard method to measure the height of an artifact used as a calibrator for observation instruments in nanotechnologies and nanosciences. The artifact is a grating specially manufactured so that its features (height, pitch, width, wall angles) are highly uniform across its area. A Linnik microscope designed for longitudinal (vertical) measurements using the principle of white light interferometry was used to determine the height of the grating. To insure the traceability of the measurements a laser source of known wavelength was used and the measurements obtained using white light were calibrated to it. The experimental data was statistically analyzed and the measurement precision was estimated to be in the range of nanometers. The data were compared with the results obtained using the TIC method with a Carl Zeiss microscope.
In micro- and nano- device fabrication technology, localized material removal is one of the basic operations for structure
formation. Classical methods for structure formation on the surface of a silicon wafer are based mainly on chemical
processing, starting with photo etching, chemical etching, and chemical-mechanical linearization. In order to propose
new methods of higher quality from the point of view of both environment protection and processing quality, we have
studied the possibility of thin films controlled removal under the action of laser radiation. We are presenting some
qualitative results of laser induced surface removal of polymer thin films, of interest for microelectronic industry (e.g.
photoresist), under the action of different laser sources. As laser sources we have used the most spread and
commercially available laser systems with different wavelengths and pulse lengths in order to compare their action on
the surfaces and to establish the characteristic parameters for removal of thin layers for surface cleaning.
In this paper a Fourier transform digital holography experimental arrangement is presented. It is actually a hybrid
arrangement, half digital half analog. The Fourier hologram was constructed using the analogous means of the so called
lensless configuration. The hologram was recorded digitally by a camera with a large CCD array in stead of the
recording medium. The recording of the image was analyzed with a computer and the original image was reconstructed
by means of the discrete Fourier transform.
This paper deals with optical characterization of photo-polymer gratings for parameter control. The gratings were
obtained using the photoinduced single step inscription of refractive optical elements technique. The optical
characterization was done by measuring the specular and diffracted orders of a laser beam incident on the grating. This
technique is specifically known as scatterometry. The laser was a He-Ne with 633 nm wavelength. The measured
diffraction efficiencies contain information about the parameters to be determined of the grating, such as pitch, linewidth
and shape of the ridges.
In this paper a simple method for determining the wavelength of an unknown source, (a problem of great theoretical and
practical importance), based on the Moire fringes phenomenon and Fourier analysis is presented and put into practice.
The accuracy and the simplicity of the problem makes it attractive and competitive.
The paper presents measurements of magnetic liquids shaping by use of magnetic fields or gravitation and centrifugal
forces. These measurements are conducted with the goal of evaluating the characteristics of the magnetic fluids in order
to obtain an adaptive system. Values of frequency response domain, pattern imposed configuration response, and free
surface curvature were measured. Three types of optical arrangements were used to determine the parameters: schlieren,
Fizeau type interferometer and triangulation optical scheme.
Surface-relief photo-polymer gratings obtained through the novel technique of photoinduced single step inscription in
photopolymers are characterized through various investigations means, with an emphasis on scatterometry. The
characterization of the gratings is necessary not only for insight in the creation process of gratings but also for checking
the reproducibility and uniformity. The diffraction efficiencies of the various orders diffracted by the grating were
measured and they were fitted to theoretical predictions corresponding to various structure models of the gratings. The
fitting procedure is used to provide the parameters of the gratings, such as the width, the grating height, the pitch or
shape factors, such as the wall angles for a trapezoidal structure. The shape of the gratings was quite complicated and the
fitting, for this reason, a challenge. Numerous models were proposed, tried and their advantages and shortcomings
We discuss an experiment for detecting small deformations by speckle interferometry. Vibration modes of an
aluminium plate are observed by digital speckle pattern interferometry (DSPI). A Mach-Zender interferometer
arrangement is used and the speckle interferograms are recorded with a CCD camera and processed on a computer.
These fringes depend on the path differences due to the vibration of the aluminium plate from its original state.
Vibration amplitudes between 0.3-0.6 &mgr; were measured for seven vibration modes.
The refractive index of a material medium is an important optical parameter since it exhibits the optical properties of the
material. The adulteration problem is increasing day by day and hence simple, automatic and accurate measurement of
the refractive index of materials is of great importance these days. For solid thin films materials Abeles method
was reconsidered. Quick, measurements of refractive index using simple techniques and refractometers can help
controlling adulteration of liquids of common use to a greater extent. Very simple interferometric set-up using Fizeau
fringe patterns compares the fringe pitch as obtained in a cell with two levels: one down level with the unknown
refractive index liquids and the upper level with gas air. A CCD matrix and a PC can handle the data and produce the
results up to for digits.
A new approach to metrology for the range below 100 nm is based on large fiducial grids optical encoders produced by
interference / lithography. Since the encoder can only be as accurate as the grating scale, advance in this area depends
on the availability of encoder plates of nanometer accuracy. Various commercially available or home made holographic
gratings were checked using interferometric methods and compared with the AFM device results. The budget of errors
was analyzed and the necessary improvements of measuring technology are presented.
Proper calibration of any instrument is vital to an investigator's ability to compare laboratory experiments, as well as to
draw quantitative relations between experimental results and the real objects. Traceability is a term used to certify an
instrument's accuracy relative to a known standard. Because traceability to meter is a very expensive and complicated
process, accurate and traceable calibration of lateral and vertical standards (e.g. 1D and 2D gratings) is a basic
metrological task for nano- and micro- technology. On the other hand laser interferometry is the de facto method to
transfer the meter standard to practical measurement. In this lecture, we describe interferometric vertical and lateral
calibration of a grating used to quantify the parameters necessary for proper translation of AFM data into physically
In this paper we investigate the vibrations of a square aluminium plate by speckle interferometry means. Modes of
vibration of this plate are shown as speckle interferograms. As usually is the case with such interferograms, enhancement
and filtering of these images is needed after recording. The speckle index and the signal-to-noise ratio (SNR) of the preprocessed
interferograms before and after filtering are calculated. An improvement of the SNR between 1.37 and 1.81 is
obtained for the vibration modes presented here.
This paper presents a numerical method for processing the fringes obtained when two waves, with a quadratic phase
difference function, interfere. As a particular case of this kind of fringes are the Newton's rings. The numerical method
we present is based on the discrete Fresnel (Fourier) transform of the data and it has the same precision as the least
square fitting (LSF).
Laser interferometer displacement measuring transducers have a well-defined traceability route to the definition of the
meter. The laser interferometer is de-facto length scale for applications in micro and nano technologies. However their
physical unit -half lambda is too large for nanometric resolution.
Fringe interpolation-usual technique to improve the resolution-lack of reproducibility could be avoided using the
principles of absolute distance measurement. Absolute distance refers to the use of interferometric techniques for
determining the position of an object without the necessity of measuring continuous displacements between points.
The interference pattern as produced by the interference of two point-like coherent sources is fitted to a geometric model
so as to determine the longitudinal location of the target by minimizing least square errors. The longitudinal coordinate
of the target was measured with accuracy better than 1 nm, for a target position range of 0.4μm.
We present preliminary experiments for an integrated optical sensor based on a Mach-Zehnder interferometer for
biological applications. The sensor is sensitive to refractive index change produced by the presence of a biological
species in the cladding of the optical waveguide. A "window" can be patterned in the upper cladding, so that the
evanescent wave can be in direct contact with the environmental (the sensitive layer). We investigated as optical
waveguides a new material, SU-8, a negative photoresist well known from the development of 3D micromachmed
structures. We structured, by photolithographic techniques, rib and channel optical waveguides. We studied the influence
of the silicon substrate on propagation losses and the possibility to use these losses for the selective attenuation of the
higher order modes on the vertical direction. As biological materials we experimented collagen, which is a bio-polymer
which can bind different enzymes or antibodies.
Presented in this paper are numerical algorithms necessary to determine the surface error by means of optical
interferometry. These algorithms are based on digital processing of phase-modulated fringe patterns, and are using the
discrete Fourier transform method.
Our paper provides analytical expressions for the statistical errors related to statistical processing of digitally recorded Newton's rings interference patterns by least squares fitting. These results completes some of our previous papers concerned with Newton's rings fringe patterns processing, which well describe an iterative numerical algorithm that we commonly use for fringe processing.
A grating type interferometer uses a grazing reflection on the testing surface. The grazing reflectance could be very large and the projected roughness height on the incident light directions is small. We built such an interferometer using a diffractive optical element (DOE) realized in National Institute of Microtechnology. We obtain resolvable quality fringes for different materials from industrial quality metal pieces to wood. Contour map of a testing flatness metallic proof is obtained followng a 4 step algorithm: smoothing for both direction of interferogram, skeletonizing interference fringes, computing heights that correspond to the deviation from a plan surface for each fringe point; representing 3D contour lines of equal (400 nm) height.
The interest to use laser surface processing in microtechnology as a friendly method from the technologic and environmental point of view lead our studies about laser radiation interaction with photo-resist and metallic thin films. In this view we have tried in our experiments to process metallic thin films deposited on silicon substrate by using laser radiation. To obtain a good quality of the metallic thin film removal from the silicon surface a careful selection of the incident laser intensity, number of pulses and irradiation geometry is needed. The threshold value for the laser cleaning intensity depends on the number of incident laser pulses. A careful experimental estimation of the cleaning conditions from the point of view of incident laser energy, fluence, intensity and irradiation geometry was realized for aluminum, copper, and chromium thin films.
The development of MEMS microsystems can be increased by integration of optically active parts. Micromachining techniques allow the fabrication of monolithically integrated Fabry-Perot microcavities, avoiding hybrid assembly technique, which is a combination of etching and wafer bonding. These microcavities can be used as sensors, as modulators or as tunable optical filters. We investigated different mirror materials: silicon nitride and polysilicon and different sacrificial layers: polysilicon and phosphorus doped silicon dioxide (PSG), using LPCVD and CVD techniques. Different arrays and shapes for the top mirror, which is movable, were analyzed in order to establish a structural material with low tensile stress. The optical constants were determined by spectrophotometric methods. Experimental data and simulations were compared.
Our paper concerns with statistical processing of digitally recorded straight equispaced fringe patterns. We determine the highest degree of accuracy that can be achieved in estimating fringe parameters by statistical processing in given statistical fluctuation conditions affecting the recorded image.
Our paper concerns with statistical processing of digitally recorded straight equispaced fringe patterns by a numerical method based on discrete Fourier transforming (DFT) of the input data, which has the advantage of faster computation than the usual least square fitting method, that we have presented in a previous paper. This new method leads to the same accuracy as the least square fitting method and it is more convenient to use for processing fringe pattern with high harmonic order features.
When dimensional measurement of a body are performed by laser beam scanning, some sources of errors must be taken into account and evaluated. They relate to: laser noise, non-linearity and reproducibility of the scanner movement, optics aberrations, body edge detection, data processing. The paper presents the results of error investigation in contact-less dimensional measurement by laser beam scanning.
A numeric algorithm for processing Newton's rings fringe patterns is presented. The interference images of this type have a characteristic appearance which can be described mathematically by a function depending on a set of parameters. The algorithm consists in finding the parameters of this mathematical expression by means of fitting the pattern using the least squares method, specially implemented with an iterative procedure. Unlike other processing methods which also use statistical calculus, this algorithm efficiently utilizes the whole information contained in the image and ensures the highest degree of accuracy, in given statistical fluctuation conditions affecting the image.
The phenomenon of phase retardation in the waist region of a gaussian beam (known as the Guoy effect) is described and demonstrated in the visible wavelength range. Two gaussian beams, originating from the same laser, are made to interfere in a region around the waist of one of them and far from the waist of the other. The relative phase is measured by processing the interference patterns recorded at different locations on the axis. A comparison with the theoretical results is carried out.
A new method of processing Newton's rings fringe patterns is presented. After the center of the circular rings is found, a special type of pixel intensity spectrum is calculated, in which the 2D pattern is reduced to a 1D profile showing a periodic structure of fringes. By further processing the parameters of the initial interferogram can be easily extracted. The statistical nature of the method leads to a higher accuracy and a better immunity to noise.
Wavelength measurement is a critical topic in many applications. Stationary interferometers, such as Fizeau and Murty, can be successfully used, considering the proportionality between the wavelength and the fringe spacing in the interference pattern.In this work we present a 1D algorithm for the calculation of the fringe spacing and error sources. The final accuracy that can be achieved is also assessed. The experimental data are taken from fringe pattern recorded with a Murty interferometer.
Speckle interferometry for non destructive testing of out of plane or in-plane stresses or deformations of rough mechanical parts is a powerful and modern technique. Basics of speckle phenomena and interferometry in specked light are reviewed. Electronic speckle pattern interferometry for vibration analysis and a Duffy-Young digital camera for in- plane measurement are presented.
The method and experimental results of circularity measurements by optical triangulation are presented. The measuring system is a laser based one, using a bi-cell detector with rectangular active surface shape and diagonal gap. The measured data were fitted with a parametric function depending on the position of the tested object center, relative to the center of the rotating table. A resolution of 2.5 micrometers /mW is reported. This sensitivity is satisfactory for the majority of industrial applications-- circularity measurement and centering.
A new self-calibration principle for phase shift interferometry is introduced, involving a whole-field consideration of the information contained by the interferograms. The principle is illustrated for the three-sample case, which was previously known as not having a self-calibration capability. Three related self- calibrating algorithms for phase shift interferometry are proposed, all of them based on this principle. The input of the algorithms is the set of three interferograms, and the output consists in both the correct phase shifts and the phase map of the wavefront being analyzed. No information on the actual phase shifts has to be supplied.
Accurate dimensional measurement is a stringent demand of today technology. Sometimes, the measurement is difficult because the body under test is not touchable. A modern solution of these two problems is contactless dimensional measurement by laser beam scanning. A moving mirror, driven by a scanner, reflects the incident He-Ne laser beam and forces it to describe a plane. A collimator transforms the plane in a parallel one, which defines the measuring field. When the test body is in the measuring field, it generates a shadow area, with a length proportional to the dimension of the body. This light distribution focuses on the surface of a photo-detector and then the electronic system processes it in order to display the results of the measurement. To prove this method, a set-up has been developed; its block-diagram is presented and the preliminary results are reported. Measuring range is (2 - 75) mm, resolution is of 1 micrometers and the accuracy is +/- 10 micrometers (2 (sigma) ).
The measurement of large angles is still an actual problem in metrology. Interferometric methods based on Michelson interferometer have high sensitivities, precision and accuracy but the angular range is limited. Two methods are presented: hollow roof prism on a rotating table and a plane-parallel plate in the interferometer's arm, as systems for angular measurements.
An interferometric set-up able to measure angles as large as +180 degree(s) is presented. The principle of the method is to measure a linear displacement (translation) produced by a crank-gear mechanism which converts the angular movement of a rotating table. The optical scheme and consideration on the accuracy of the method are presented.
Complex refractive index determination (refractometry) of metals can be made successfully with methods using reflectivity measurements. In this paper a brief classification of reflectivity methods with subsequent comments about their sensitivity is made. Experimental results obtained using the most suitable methods are presented.