A fully digital experimental set-up for real-time digital acquisition and digital optical reconstruction of holographic sequences is presented: a He-Ne laser, a CCD camera and a Phase Only Spatial Light Modulator (SLM) area are part of the set-up. CCD registering and SLM projector are working simultaneously. Using a custom made software of our own, real-time Digital Holographic Interferometry (DHI) “fringe motion pictures” can be performed by subtracting consecutive frames from a reference one and instantly displaying the differences on the SLM illuminated with a playback wave. Phase variations of the objects can be visualized in real-time by observing the interference fringe pattern evolution.
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.
KEYWORDS: Reconstruction algorithms, Signal to noise ratio, Multiplexing, Image quality, Photodiodes, Sensors, Modulation, Micromirrors, Signal to noise ratio, Image processing, Digital micromirror devices
Single-pixel imaging based on multiplexing is a promising technique, especially in applications where 2D detectors or raster scanning imaging are not readily applicable. With this method, Hadamard masks are projected on a spatial light modulator to encode an incident scene and a signal is recorded at the photodiode detector for each of these masks. Ultimately, the image is reconstructed on the computer by applying the inverse transform matrix. Thus, various algorithms were optimized and several spatial light modulators already characterized for such a task. This work analyses the imaging quality of such a single-pixel arrangement, when various illumination conditions are used. More precisely, the main comparison is made between coherent and incoherent ("white light") illumination and between two multiplexing methods, namely Hadamard and Scanning. The quality of the images is assessed by calculating their SNR, using two relations. The results show better images are obtained with "white light" illumination for the first method and coherent one for the second.
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.
Compressive sampling is a technique used in digital signal processing, which allows for the capture of high resolution physical signals from relatively few measurements. This technique is illustrated here for two simple cases: a signal to be that can be expressed as a sum of three sine functions and another one that can be expressed as a sum of three Bessel functions of the first kind. In order to perform a compressive sampling one must use correct measurement vectors and this is a quite complicated problem. In this paper a simple algorithm for obtaining the correct measurement vectors for illustration and pedagogical purposes is shown.
In this paper we discuss a study and application of the optical properties of liquids in the terahertz range and a possible technique for identifying liquids. The optical properties are the reflection and transmission of the radiation at various interfaces between known media and between a known medium and the unknown medium and the complex refractive index which is to be determined from measurements of the change in radiation signal after multiple optical interactions inside a silicon prism. For this purpose we use an attenuated total reflection experimental arrangement. We show that one can identify liquids placed on the top of the prism turned upside down using this method. Terahertz waves are especially useful in this context because they allow the determination of the liquid content of containers that are difficult to open or that simply cannot be opened, such as luggage in airports. Some explosives are liquids and the identification of the liquids using terahertz waves may help detecting hidden explosives.
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.
This paper produce formulae for the power reflection and transmission coefficients of a uniaxial thin film sandwiched between two isotropic media and the necessary intermediate formulae of the field reflection and transmission coefficients at the planar interface between a isotropic and a uniaxial media in explicit form. The formulae obtained are tested successfully using the criteria of conservation of energy and the conservation of the form of the equations for time reversal.
A phase-shifting interferometry method to measure the wavefront reflected from a deformable mirror is described.
Usually, an adaptive optics system encompasses a deformable mirror and a Shack-Hartmann wavefront sensor as the
main components. However, an interferometric method is suited for calibration and traceability purposes of such
measurements. In this regard, we developed a system able to characterize the wavefront in situ with both a Shack-
Hartmann sensor and a phase-shifting interferometer. The method encompasses a reflective diffraction grating, where the
plus-first diffraction order reflected off the grating was incident on a deformable mirror. This beam was then reflected
back to the grating where it interfered with the incident beam and the interference pattern was collected on the minusfirst
order. As with the four-step phase-shifting interferometry method, four interference patterns were recorded and
processed to extract the wavefront information. The wavefront sensor recorded the wavefront directly reflected from the
deformable mirror, via a beam splitter.
The sampling theorem can be described as a economic way of representing a limited bandwidth function. A sample of
points is chosen and an interpolation function of these points is used to represent the function. The great importance of
this fact is that paves the way to discrete computation. The sample points act as a sort of “highlight” points of the
original function, and computation involving the entire function may be restricted to calculation using only the sample
points. Moreover we were able to find some refining of the classical outline of the sampling theorem that improves its
precision bringing also some physical insight into the core of the theorem. Of course also these consideration are not
restricted to optics, they can be construed as general properties of the signal theory. But we were optically minded at all
times and most of the applications are in optics.
A grating interferometer that uses the high diffraction orders in conjunction with a Twyman-Green commercial interferometer is used for the measurement of in plane movement of gratings. The high diffraction orders ensures the amplification of the measurement precision with a factor equal to the diffraction order of the measurement in principle, because no imaging of features marking the beginning and the end of the measured length feature is necessary, and therefore the resolution limits associated with microscope imaging are eliminated.
Ellipsometry is a convenient means to ascertain electro-optic properties, and the null-type methods are particularly
so because they do not require a powermeter. Electro-optic materials like Strontium Barium Niobate (SBN) with the
symmetry axis normal or parallel to the surface are materials suitable for thin film integrated optic devices, therefore of
practical interest. For this reason we endeavoured to devise and to test experimental arrangements that measure the
birefringence of uniaxial structures with the symmetry axis parallel and perpendicular to the surface.
The discovery of the Fast Fourier transform (FFT) algorithm by Cooley and Tukey meant for diffraction computation
what the invention of computers meant for computation in general. The computation time reduction is more significant
for large input data, but generally FFT reduces the computation time with several orders of magnitude. This was the
beginning of an entire revolution in optical signal processing and resulted in an abundance of fast algorithms for
diffraction computation in a variety of situations. The property that allowed the creation of these fast algorithms is that,
as it turns out, most diffraction formulae contain at their core one or more Fourier transforms which may be rapidly
calculated using the FFT. The key in discovering a new fast algorithm is to reformulate the diffraction formulae so that
to identify and isolate the Fourier transforms it contains. In this way, the fast scaled transformation, the fast Fresnel
transformation and the fast Rayleigh-Sommerfeld transform were designed. Remarkable improvements were the
generalization of the DFT to scaled DFT which allowed freedom to choose the dimensions of the output window for the
Fraunhofer-Fourier and Fresnel diffraction, the mathematical concept of linearized convolution which thwarts the
circular character of the discrete Fourier transform and allows the use of the FFT, and last but not least the linearized
discrete scaled convolution, a new concept of which we claim priority.
We extrapolated the lucky imaging technique, mostly used in astronomy, to the field of interferometry for displacement measurement. From the batch of interferograms generated by a Twyman-Green-type interferometer and acquired by a CCD camera, those with high overall contrast were selected and fitted to a sinusoidal function. The high-contrast interferograms showed a significantly lower dispersion and, consequently, a lower uncertainty of the measured displacement.
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.
A spatial light modulator is a matrix-shaped device able to modify the amplitude or the phase of the reflected or
transmitted light, which can be operated pixel by pixel independently. This opens new possibilities for rapid and efficient
manipulation of the light diffraction but also brings us close to the ambiguous boundary between physical and digital
optics, or more precisely between the continuous and the discrete mathematical approaches of diffraction. In this article
we show a series of diffraction experiments in which we use the modulator to simulate various optical elements,
physically real or not, recorded real or computed holograms, experiments in which due to the discrete nature of the
modulator we are liable to use alternately the discrete and the continuous approach. To avoid ambiguities we have to
keep track of the approaches we use, and also, more importantly, to be able to switch from discrete to continuous terms
and vice-versa.
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.
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.
KEYWORDS: Digital holography, Holograms, Fourier transforms, 3D image reconstruction, Holography, Analog electronics, Image analysis, Digital cameras, Digital recording, Transparency
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.
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.
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.
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
discussed.
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.
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.
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
meaningful data.
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.
The Abelès method is a classical method for determining the refractive index of dielectric thin films, based on the
phenomenon oftotal transmission of p-polarized light at the Brewster angle ofincidence. In this paper we examined the
main features of the method, such as the criterion for ruling out spurious solutions, in a formal manner, using closed
form equations. We also investigated the method for ambiguities and we found out using rigorous analysis that the
method is ambiguous, because there are unreported situations in which the spurious solutions cannot be distinguished
from the real solution. The limits within which the method can be used, even in situations when ambiguities exist, are
determined.
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).
Rigorous Coupled-Wave Analysis for 2D gratings is reviewed. The main features of RCWA such as the Fourier
expansion of the dielectric function in the grating area, solving the Maxwell equation inside the grating, the eigenvalue
problem and the matching of the tangential fields at the interfaces are described. Key improvements of the theory, that
allows the reduction of the work time by orders of magnitude, such as the reduction of the sue of the matrix for the
eigenvalue problem are stressed. The computer code written based on this theory passed consistency tests and was
checked against other computer codes.
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.
In this paper we present the design and the experiments performed to obtain a micromechanical voltage tunable Fabry-Perot interferometer integrated with a p-n photodiode on a silicon substrate. It can be used as a voltage tunable filter for the input radiation or as a voltage controlled attenuator to regulate the light from a monochromatic source. Different solution have been analyzed and experimented. The top mirror of the Fabry-Perot cavity is a doped poly-Si or Au/SiO2 movable membrane, electrostatically actuated, obtained using Si micromachining. A complex design process was performed: optical, electomechanical and technological. All these phases were performed interactively. Different materials were considered in order to perform an optimum design. Experimental micromachined interferometers were obtained using two techniques: (1) surface micromachining, and (2) anisotropic etching of (111)-oriented Si wafers, combined with an isotropic pre-etching step. These processes were optimized and matched to the photodiode fabrication process. Monolithic integrated interferometers coupled to p-n photodiodes were obtained.
In this article are demonstrated the nanoscale capabilities of scatterometry, an optical metrology technique for the determination of the grating parameters. Notably, for both ellipsometric-scatterometry and phase-moudlation scatterometry we are now currently using shorter wavelength laser soruces, namely 325 nm in UV. We added to the scatterometer the ability to perform Φ-scanning measurements. This capability adds new degrees of freedom to the sensitivity optimization procedure. Because the sensitivity analysis formalism leads us to the conclusion that sensitivity is provided mainly be anomalies, a rigorous analysis of a certain type of anomaly, the most likely to occur for our type of samples, was made using Modal Analysis. Our analysis allows for the prediction of the anomaly position. This procedure allows us to find the optimum measurement configuration much faster than the SAF formalism used in the past.
Phase-modulation scatterometry is a metrology technique for determining the parameters of gratings using as a key device a phase modulator. For measurement purposes the phase modulator requires a complicated calibration procedure that is analyzed here in detail. The main source of error to be dealt with are the fluctuations of the phase modulation amplitude. The measurables are the direct term and the first two harmonics of the output. For the fitting of the experimental data we used the ratio of the harmonics to the direct term because it improves significantly the accuracy. A sensitivity analysis was performed for two samples, one real and one theoretical, to find the measurement configuration that insures optimum determination precision for the grating parameters. For the real sample, comparisons of the theoretical predictions for sensitivity with the actual values showed a good agreement. For both samples the sensitivity analysis indicated sub-nanometric precision for the critical dimension (grating linewidth).
In the work reported here, we discuss the measurement precision of two scatterometry techniques, the variable angle and the variable wavelength techniques. The issue of interest is the measurement precision of the sample parameters. This is determined by both the sensitivity of the diffraction measurable to changes in sample parameters and the precision with which the measurable can be determined. This approach includes taking into account the correlation effect between the contribution to the measurable of the various grating parameters to be determined, such as linewidth and height. The comparison of the theoretical predictions of precision for angle-resolved and wavelength-resolved scatterometer measurements shows no conclusive hierarchy. Practical considerations, however, indicate that angular-resolved scatterometry is a more advantageous technique. For both methods, decreasing the wavelength of the light source improves the determination precision of the sample parameters.
To investigate the optical homogeneity of crystals some methods based on the analysis of the laser beams interacting with a sample have been recently proposed. The emergent beam is acquired by a data acquisition/image processing system which offers the possibility for both local and global analysis of the sample. Combined with microscopy techniques these methods enable the study of submicron defects such as scattering centers, clusters of punctual defects, microcracks. A map of the absorption coefficient (alpha) equals(alpha) (x,y) can be obtained by recording the transmitted light when scanning the sample with the laser beam. This result is particularly useful for determining some growth parameters because spatial variation of the absorption coefficient is a consequence of thermal oscillations in the crystallization system. Our paper is a short study on the optical homogeneity of sapphire crystals grown by different techniques as related to the particular defects induced by the growth process. Laser beam analysis has been mainly employed to characterize the samples. The results provide important information on the dynamics of the crystallization interface during the growth processes, on the number and types of growth defects, foreign phase precipitations, inclusions, thermal stress, etc., which may help with optimization of the growth parameters.
The sensitivity analysis of fitting (SAF) is a formalism that determines the type of measurements that yields optimum determination precision. SAF is applied to ellipsometric- scatterometry of surface relief gratings and for the optimum measurement configuration predicts a significant improvement compared to the conventional scatterometry measurement configurations. The SF predictions for precision are compared to actual values obtained experimentally, and a qualitative agreement is obtained. The discrepancies between theory and experiment are likely due to inaccurate modeling of the grating.
Scatterometry, the analysis of light diffraction from periodic structures, is shown to be a versatile metrology technique applicable to a number of processes involved in the production of microelectronic devices, flat panel displays, and other technologies which involve precise dimensional control of micron and sub-micron features. This paper reviews metrology issues and requirements of these technologies and gives details on one application of scatterometry for illustration. Scatterometer results are compared to measurements of the same samples using other metrology techniques, including cross- section SEM, top-down SEM, AFM, and ellipsometry.
This paper reports on controlled electric and optical properties of single crystalline sapphire for substrates use. The crystals were grown by the Czochralski method from a graphite crucible by using an original non-conventional crystal growth assembly. We paid a special attention to the homogeneity of the crystal. A new model for the electric conduction mechanisms is considered, the validity of which was confirmed by experimental measurements.
Conventional scatterometry measures the intensity of a diffraction order from a periodic structure as one or more measurement parameters is changed. We have previously demonstrated conventional techniques to characterize developed photoresist linewidths as small as approximately 0.15 micrometer, with scatterometer results agreeing well with measurements performed using other techniques. For developed photoresist, the measurement sensitivity of conventional scatterometer techniques diminishes considerably for sample linewidths that are sub-0.1 micrometer, using 633 nm laser illumination. We present a modified scatterometer configuration which combines aspects of conventional scatterometry and ellipsometry that provide increased sensitivity for characterizing sub-0.1 micrometer linewidth periodic photoresist structures. The complex reflection coefficients representing the grating sample are extracted, both in magnitude and in relative phase, through intensity measurements at selected polarizer/analyzer/compensator orientations. The cross-polarization terms of the reflection coefficient matrix are shown to be equal for a symmetric photoresist grating structure with line widths approximately 0.5 micrometer. Theoretical results for nominal 70 nm photoresist lines are presented that show phase measurement sensitivity to linewidth changes on the order of 2 - 4 deg/nm and reflectance sensitivity of at least 3%/nm. This results in linewidth measurement resolutions that are sub-nm.
KEYWORDS: Interferometry, Interferometers, Data processing, Signal generators, Physics, Laser interferometry, Optical testing, Digital signal processing, Transform theory, Signal detection
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.
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.
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.