Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/12—Generating the spectrum; Monochromators
  • G01J3/14—Generating the spectrum; Monochromators using refracting elements, e.g. prisms
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/40—Measuring the intensity of spectral lines by determining density of a photograph of the spectrum; Spectrography
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
  • G01J3/0216—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using light concentrators or collectors or condensers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
  • G01J3/0218—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using optical fibers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
  • G01J3/0224—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using polarising or depolarising elements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0294—Multi-channel spectroscopy
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/2803—Investigating the spectrum using photoelectric array detector
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3577—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing liquids, e.g. polluted water

Definitions

• This invention relates generally to an apparatus and method for simultaneously determining an LR spectrum of multiple sample materials. More particularly, the disclosed invention relates to spatial multiplexing of spectroscopically determined IR spectra of multiple samples using an apparatus and method that operate in real-time with simultaneous background compensation, and which do not require the use of any moving parts. Still further, the apparatus and method of the disclosed invention do not require extensive mathematical transformation of the detected spectral information to analyze the composition of the sample material.
• the disclosed invention has industrial applicability to, for example, a real-time method to monitor manufacturing processes.
• Such processes include, but are not limited to measurement of thickness, chemical structure, and orientation of coatings on surfaces (solid, liquid, chemically bound, physically adsorbed). These measurements include, but are not limited to those made on biological materials, polymers, superconductors, semiconductors, metals, dielectrics, and minerals.
• Further applicability is found to a real-time apparatus and method to measure and detect a chemical species present in a chemical reaction involving various processing of materials in any of a gaseous, liquid, or solid state.
• the apparatus and method of this invention provides for self-compensation, to account for sensor or optical path changes over time, or changes in environmental conditions, which may affect the measurements obtained.
• Spectrometric techniques are often used in analysis of materials.
• Classically, spectroscopy is the measurement of the selective absorption, emission, or scattering of light (energy) of specific colors by matter. Visible white light can be separated into its component colors, or spectrum, by a prism, for example.
• the principal purpose of a spectroscopic measurement is usually to identify the chemical composition of an unknown material, or to elucidate details of the structure, motion, or environmental characteristics (e.g., internal temperature, pressure, magnetic field strength, etc.) of a "known" material or object.
• Spectroscopy's widespread technical importance to many areas of science and industry can be traced back to nineteenth-century successes, such as characterizing natural and synthetic dyes, and determining the elemental compositions of stars.
• IR infrared
• LR radiation does not have enough energy to induce transitions between different electronic states, i.e., between molecular orbitals, as seen with ultraviolet (UV), for example.
• UV ultraviolet
• IR spectroscopy examines vibrational transitions within a single electronic state of a molecule, and is not concerned with specific atomic elements, such as Pb, Cu, etc.
• Such vibrations fall into one of three main categories, i.e., stretching, which results from a change in inter-atomic distance along the bond axis; bending, which results from a change in the angle between two bonds; and torsional coupling, which relates to a change in angle and separation distance between two groups of atoms.
• Almost all materials absorb LR radiation, except homonuclear diatomic molecules, e.g., O 2 , H , N 2 , Cl 2 , F 2 , or noble gases.
• LR typically covers the range of the electromagnetic spectrum between 0.78 and 1000 ⁇ m. Within the context of IR spectroscopy, temporal frequencies are measured in "wavenumbers" (in units of cm “1 ), which are calculated by taking the reciprocal of the wavelength (in centimeters) of the radiation. Although not precisely defined, the LR range is sometimes further delineated by three regions having the wavelength and corresponding wavenumber ranges indicated:
• An electronic state of a molecular functional group may have many associated vibrational states, each at a different energy level. Consequently, IR spectroscopy is concerned with the groupings of atoms in specific chemical combinations to form what are known as "functional groups", or molecular species. These various functional groups help to determine a material's properties or expected behavior by the absorption characteristics of associated types of chemical bonds. These chemical bonds undergo a change in dipole moment during a vibration.
• the LR absorption bands associated with each of these functional groups act as a type of "fingerprint" which is very useful in composition analysis, particularly for identification of organic and organometallic molecules.
• Lnfrared spectrometers may be built using a light source (e.g., the sun), a wavelength discriminating unit or optically dispersive element such as a prism, for example, and a detector sensitive to LR.
• a light source e.g., the sun
• optically dispersive element such as a prism
• detector sensitive to LR By scanning the optically dispersive element, spectral information may be obtained at different wavelengths, by using either a reflection mode, i.e., reflection of the light source off the sample, or a transmission mode, i.e., transmitting a portion of the light source through the sample.
• a reflection mode i.e., reflection of the light source off the sample
• a transmission mode i.e., transmitting a portion of the light source through the sample.
• one drawback to this approach is the moving parts associated with the required scanning operation. Such moving parts inherently limit the ruggedness and portability, for example, of such a device.
• a Michelson interferometer has been used to generate a so-called interfere gram in the LR spectrum, which later is subjected to Fourier transform processing such as a fast Fourier transform (FFT) to yield the final spectrum.
• FFT fast Fourier transform
• spectrometers are called FTLR interferometers, and the first commercially available appeared in the mid 1960's.
• a representation of an FTLR interferometer is provided in Fig. 1.
• FTLR interferometer 100 provides a means for the spectrometer to measure all optical frequencies transmitted through sample 120 simultaneously, modulating the intensity of individual frequencies of radiation before detector 160 picks up the signal.
• moving mirror arrangement 150 is used to obtain a path length difference between two (initially) identical beams of light. After traveling a different distance than a reference beam, the second beam and the reference beam are recombined, and an interference pattern results. TR detector 160 is used to detect this interference pattern.
• the detected interference pattern, or interferogram is a plot of intensity versus mirror position.
• the interferogram is a summation of all the wavelengths emitted by the sample and, for all practical purposes, the interferogram cannot be interpreted in its original form.
• FT Fourier Transform
• a computer or dedicated processor converts the interferogram into a spectrum that is characteristic of the light either absorbed or transmitted through sample 120.
• FT interferometers are mostly limited to laboratory conditions which require the use of an optical bench to prevent vibration, and which also require stringent environmental controls to control temperature variations that adversely affect the interferogram by thermally inducing path length differences. While this type of scanning approach has proven to be workable, the signal-to-noise-ratios (SNR) obtainable in some situations often require substantial signal averaging of multiple interferograms, thus making FTLR systems inherently slower than desired under some circumstances, with reduced speed and potentially lower reliability resulting from the numerous moving parts of these systems.
• SNR signal-to-noise-ratios
• Ln spectroscopy, resolution is a measure of the ability to resolve or differentiate two peaks in the spectrum, where high resolution corresponds to a small wavenumber difference between the peak positions, and low resolution is associated with a larger wavenumber difference between the peak positions.
• Fourier Transform interferometers are capable of extremely high resolution, on the order of 171000 th cm “1 , depending on the amount of possible movement of the mirror, or the path length difference that can be generated by the particular apparatus.
• "Low” resolution is generally considered to be in the range of 16-32 cm “1 , although no bright-line demarcation between "low” and "high” resolution exists, as resolution is chosen based on the required measurement and specific application.
• Air-Bearings Requires stable supply of clean, dry air and a tightly leveled travel plane for the moving mirror. Low tolerance for vibration.
• Magnetic Coils Requires highly regulated power supplies.
• FTLR Magnetic/Piezo Hybrid Requires large mechanical structures and complicated feedback system for piezo element operation.
• FTLR has been applied to a variety of studies in industry, government, and academic laboratories, and has resulted in a major improvement upon conventional methods of performing analysis on a variety of samples.
• the moving mirror mechanism in a traditional interferometer has limited the design and construction of a more compact and portable FTLR.
• spectroscopy based on dispersion provided a possible implementation. Ln this approach, an optically dispersive element, such as a prism or diffraction grating, is used to separate the spectral frequencies present in the incident light radiation. The dispersive element was then rotated, in order to allow the various wavelengths present in the incident light to be detected.
• an optically dispersive element such as a prism or diffraction grating
• LR spectroscopy based on dispersion became obsolete in most analytical applications in the late 1960's due to its slow scan rate and lower sensitivity. It is well known that the scanning mechanism in a dispersive spectrometer, e.g., a moving prism, intrinsically limits both its ruggedness and optical throughput. The need for scanning comes from the fact that point detection of photons was the only available method at that time, and this was especially true in the LR range of the spectrum. Today, however, array detectors in the visible and near-LR range are widely available for area detection of photons.
• CCD Charge-coupled- devices
• QE quantum efficiency
• Infrared reflectance-absorbance spectroscopy is a non-destructive technique that provides direct structural information about either the expanded or condensed phase of a Langmuir monolayer.
• the technique can also provide information about both the hydrocarbon tails and the head groups independently by monitoring vibrational modes with frequencies in the 4000 to 400 cm-1 region. Because polarized infrared spectroscopic measurements are sensitive to the orientation of transition- dipole moments, LRRAS can be used to determine the orientation of different subcomponents of an amphiphilic molecule.
• PM- LRRAS polarization modulation infrared reflectance-absorbance spectroscopy
• the LRRAS or PM-LRRAS technique has been used to investigate a variety of Langmuir monolayers, including studies of fatty acid, phospholipid and phospholipid-protein monolayers.
• the technique has been used to provide information on lipid conformation, molecular tilt angle, and the structure of head groups, as well as protein secondary structure and orientation.
• neither LRRAS nor PM-LRRAS both of which utilize FTLR have been able to provide in situ time-resolved measurements of Langmuir monolayers in the 1 msec to 1 sec time regime, nor have any of the known techniques been able to simultaneously provide multiple independent measurements.
• the present invention solves many of the aforementioned problems of providing a robust, high-resolution and sensitive apparatus and method for determining background-compensated LR spectra of multiple samples, without the use of moving parts, or calculation-intensive Fourier Transform interferometric techniques.
• the multi-beam planar array infrared (PALR) spectrograph offers numerous advantages over conventional FT-LR interferometry for a variety of important materials characterization applications. Some of these include routine LR spectroscopy, time-resolved LR spectroscopy, time-resolved spectroscopic imaging, monolayer spectroscopy and on-line monitoring of processes in aggressive environments.
• the PALR spectrograph may also be used to investigate fundamental dynamics associated with thick and thin polymer films undergoing an irreversible change.
• a focal plane array (FPA) detector having a relatively large area.
• FPA focal plane array
• a 320 x 256 pixel Indium- Antimonide (InSb) FPA detector or other suitable material, may be used in the construction of the PALR spectrograph.
• Multiple beams from multiple samples or multiple spatial areas of one sample are preferably dispersed by one or more prisms or gratings, and simultaneously focused on the detector.
• At least one of these multiple samples could be a background reference sample, from which the spectrum of the background environment could be determined. This allows background compensated data from several samples to be collected simultaneously in real-time, or compensated data from several spatial locations in the same sample could be collected simultaneously.
• LR polarizers selective to certain electric field components of the LR beam can be inserted in the optical path, thus providing for simultaneous collection of LR dichroic data.
• Multi-beam PALR spectroscopy can be used for the "real-time" spatial mapping of films for quality control applications in a processing line. Compensation for environmental factors, e.g. spectral compensation for water vapor present in the optical path, or for the aging characteristics of the sensor can also be accomplished in real-time, without complicated calibration procedures. It can also be used for detection of chemical toxins and, if used in conjunction with an analyte or bio-specific reagent, it can be used to detect biological agents in the environment, e.g., virus or bacteria. Further, multiple beam PALR using the apparatus and method of the invention can also be used to measure pollutants in water, dielectric film growth in semiconductors, and the development of orientation in a polymer film production line.
• One aspect of the invention includes an apparatus for determining an LR spectrum of a plurality of sample materials using IR FPA technology to capture the LR spectral information for each of the samples, without utilizing a scanning mechanism, or any moving parts, and without the use of computation- intensive signal processing, e.g., Fourier Transform.
• This aspect includes an apparatus for simultaneously spatially multiplexing LR spectral information for each of a plurality of samples, and includes at least one LR light source; at least one sample holder which positions the plurality of samples in an optical path; an optically dispersive element in the optical path, wherein an emission from the at least one LR light source interacts with each of the plurality of samples along the optical path to form a corresponding plurality of sample emissions, said plurality of sample emissions interacting with the optically dispersive element to form a corresponding plurality of dispersed sample light beams, each of said plurality of dispersed sample light beams corresponding to a respective one of the plurality of samples; and an IR FPA detector arranged in the optical path, said LR FPA detector having multiple pixels arranged in plural rows and columns, wherein the LR FPA detector detects the corresponding plurality of dispersed sample light beams and provides at least one output which represents the TR spectral information for each of the plurality of samples.
• a real-time, non-interferometric apparatus using LR absorption phenomena and no moving parts during operation to simultaneously perform chemical analysis in a plurality of sample volumes includes a broadband light source; at least one sampling accessory for positioning the plurality of sample volumes so that at least a portion of light emitted from the broadband light source interacts with each of the plurality of sample volumes; adjustable means for optically dispersing the at least a portion of light interacted with each of the plurality of sample volumes to obtain a plurality of corresponding dispersed sample beams; a two-dimensional LR detector array having a plurality of detector elements arranged in rows and columns, optical coupling means for coupling the plurality of corresponding dispersed sample beams onto the two-dimensional LR detector array; and processor means for controlling the two-dimensional LR detector array and providing non-interferometric chemical analysis of said plurality of samples based at least upon an LR absorption spectrum in one or more particular wavelength regions, wherein each of the plurality of corresponding dispersed
• chemical analysis of the plurality of samples is performed by determining an LR absorption spectrum of each of the plurality of samples.
• the method includes projecting at least a portion of an emission of the broadband light source onto the plurality of sample volumes; interacting the at least a portion of an emission of the broadband light source with the plurality of sample volumes; providing a corresponding plurality of sample emissions to an optically dispersive element; forming a plurality of corresponding dispersed sample beams; optically coupling the plurality of corresponding dispersed sample beams onto the two-dimensional LR detector array, wherein each of the plurality of corresponding dispersed sample beams are projected on multiple rows in a different area of the two-dimensional LR detector array; non-interferometrically processing, within each different area of the two-dimensional LR detector array, an output from each detector in a plurality of rows of detectors, wherein each column of detectors represents a particular wavelength within each different area; determining the LR absorption
• the method includes providing an LR source; positioning the plurality of sample volumes in an optical path; interacting at least a portion of an emission of the LR source with the plurality of sample volumes along the optical path to form a plurality of sample emissions; optically dispersing the plurality of sample emissions to form a corresponding plurality of dispersed sample beams; detecting each of the plurality of dispersed sample beams on spatially separated areas on a focal plane array having rows and columns of pixels thereon; and simultaneously and non-interferometrically determining the LR spectrum of each of the plurality of sample emissions by evaluating a combined output from each spatially separated area of the focal plane array, wherein each column of pixels in one of the spatially separated areas represents a wavelength contained within an associated one of the plurality of sample emissions.
• an apparatus for simultaneously collecting, processing, and displaying IR spectral information for one or more samples.
• the apparatus includes a plurality of IR light sources; at least one optically dispersive element; a plurality of optical paths; an LR FPA; processing means for processing an output of the LR focal plane array and determining the LR spectral information; and display means for displaying the LR spectral information, wherein each of the plurality of LR light sources presents a different angle of incidence with respect to the one or more samples, wherein each of the plurality of optical paths directs an associated one of a plurality of reflected LR beams to a different spatial area on the LR FPA.
• a method of determining anisotropic LR optical constants of a material includes providing a substrate; projecting an LR light source onto a surface of the substrate at a non-perpendicular angle of incidence; transmitting a first transmitted portion of the LR light source through the substrate; coupling the first transmitted portion of the LR light source through an optical path and onto a first area on the FPA; providing a film material on the substrate; projecting the LR light source onto a surface of the film material at the non-perpendicular angle of incidence; transmitting a second transmitted portion of the LR light source through the film material and the substrate; coupling the second transmitted portion of the LR light source through the optical path onto a second area on the FPA; rotating a mirror in the optical path to move the second area on the FPA so as to coincide with the first area on the FPA; and determining an angle of refraction within the film material by measuring an angle of rotation of the mirror.
• a Planar Array Infrared Reflection- Absorption Spectroscopy (PA-LRRAS) arrangement for measuring an orientation of a thin film on a substrate, which includes an LR source; two orthogonally polarized filters which receive an IR light beam from the LR source; a PALR detector; and a processor, wherein two orthogonally polarized LR beams emanating from the two orthogonally polarized filters are reflected from the thin film and detected by the PAIR detector, wherein a differential reflectivity spectrum is calculated by the processor, and wherein the differential reflectivity spectrum is substantially free of any polarization-independent signals including water vapor absorptions, instrumental drifts, and signal fluctuations.
• the processor uses the calculated differential reflectivity spectrum to determine a molecular orientation of the thin film.
• a method of determining an orientation of a thin film on a substrate includes providing an TR source; producing two orthogonally polarized light beams from the LR source; reflecting the two orthogonally polarized light beams from the thin film, detecting the two reflected orthogonally polarized light beams with a PALR detector; and calculating a differential reflectivity spectrum in the processor using the two reflected orthogonally polarized light beams, wherein the differential reflectivity spectrum is essentially free of any polarization-independent signals including isotropic water vapor absorptions, instrumental drifts, and signal fluctuations.
• either direct lens coupling through an aperture, or through mid-LR optical fibers may be used to collect sample light emissions representing the samples.
• Use of optical fibers may provide desired flexibility in placement of the apparatus, and allow remote sensing of, for example, smokestacks, and also allow easier implementation of multiple channel detection and chemical analysis.
• the apparatus and method of the present invention do not require moving parts to determine spectral information.
• the method and apparatus are, consequently, well adapted to relatively harsh environments, such as, for example, high vibration environments in a manufacturing plant, or temperature extremes, as might be found in the field.
• the method and apparatus may also be used in various industrial applications to measure and detect the thickness, either in transmission or reflection mode, the chemical structure and orientation of coatings/films (solid, liquid, chemically bound, physically adsorbed) on liquid surfaces, including but not limited to water, oil and other solvents, and also to measure the thickness, orientation and chemical structure of films electrochemically deposited on solid substrates, including but not limited to metals and semiconductors.
• the multi-beam PALR spectrograph offers numerous advantages over conventional FT-LR interferometry for a variety of important materials characterization applications, including routine TR spectroscopy, time-resolved LR spectroscopy, time- resolved spectroscopic imaging, monolayer spectroscopy, on-line monitoring of processes in aggressive environments, and probing fundamental dynamics associated with thick and thin polymer films undergoing an irreversible change.
• FIG. 1 provides a representation of a conventional FTLR interferometer
• FIG. 2 provides two different schemes used for conventional interferometry based on Fourier Transform, but which do not require moving parts to generate a difference in optical path length;
• FIG. 3 A depicts an aspect of the present invention suitable for non- interferometric LR spectroscopy of multiple samples in one sample holder is accomplished using no moving parts;
• FIG. 3B depicts another aspect of the present invention in which non- interferometric IR spectroscopy of multiple samples is accomplished using multiple LR sources and optical paths, and no moving parts;
• FIG. 3C shows further optical path details for an arrangement suitable for the spatial multiplexing of multiple beams for the apparatus depicted in FIG. 3B;
• FIG. 3D shows sampling with polarized light
• FIG. 4 shows another aspect f the invention using a Pellin-Broca prism as the optically dispersive element, and which shows LR optical fiber being used to couple the light into the apparatus;
• FIG. 5 provides a graph of refractive index dispersion of ZnSe, and optical refraction for the Pellin-Broca prism of Fig. 4;
• FIG. 6 shows a configuration suitable for real-time background correction
• FIG. 7 shows an arrangement suitable for measuring multiple angles of incidence of LR radiation reflected from a surface
• FIG. 8 depicts a stratified three-phase system representative of a thin film on a substrate
• FIG. 9 shows an arrangement suitable for reflection/refraction measurement used in determining optical constants of a thin film
• FIG. 10 shows an arrangement for conventional Polarization Modulation
• PM-LRRAS Infrared Reflectance- Absorbance Spectroscopy
• FIG. 11 shows an arrangement of the invention suitable for Planar Array
• PA-LRRAS Infrared Reflectance-Absorbance Spectroscopy
• Apparatus 300 includes an LR light source 310, which may be any common LR light source, including, for example, tungsten lamps, Nernst glowers, or glowbars or, in some applications, LR radiation from the sun may be used.
• the LR source may be a LR Emitter with ZnSe window, manufactured by Cal-Sensors, for example.
• LR source 310 has a "flat" or uniform intensity across the LR spectrum, or at least a portion of the IR spectrum. However, if LR source 310 is not uniform, such non-uniformity may be accounted for during the analysis process.
• Adjustable aperture 320 is used, at least in part, to establish the resolution of the apparatus, i.e., a smaller-sized opening provides higher resolution.
• Adjustable aperture 320 may be a circular iris or, in a preferred embodiment, an adjustable rectangular slit, having a length dimension, for example, of approximately 1 cm, and an adjustable width of 0-2 mm.
• Such a slit is manufactured by RIIC, as model WH-01.
• Sampling accessory 330 positions one or more sample volumes, which contain one or more samples to be analyzed, in the optical path.
• Sampling accessory 330 may be, in a preferred embodiment, a simple sample holder, which merely positions a small sample volume of material to be sampled, e.g., polymer film, near LR source 310, or it may comprise a more elaborate sampling volume arrangement known and used for sampling gases, or may hold a plurality of samples.
• Gases which have a lower density than solids or liquids, may require such a relatively more elaborate sampling accessory having a set of mirrors or other suitable arrangement (not shown) to provide for multiple passes of the LR source through the sample volume. Such multiple passes are useful in ensuring that sufficient optical density is achieved for the LR absorption phenomena to be reasonably measured. Multiple pass arrangements may also be used, in other embodiments, to monitor smokestack emissions, or to monitor hazardous chemical fumes or vapors in laboratory, military, or industrial environments.
• Sampling accessory 330 could also comprise optics including a telescope or microscope arrangement, or coupling to a single optical fiber or bundle of optical fibers.
• apparatus 300' may include a plurality of sampling accessories 330, 331 (or more) that may be used, along with appropriate optics, to pass a portion of an emission from LR source 310 through sampling accessory 330, and a portion of an emission from second LR source 311 through aperture 321, and sampling accessory 331.
• Optically dispersive element 350 receives portions of an emission from LR light sources 310 and 311 that are passed through respective sample volumes, and reflected from mirrors 340 and 341.
• the entire LR spectrum, representative of LR source 310 may not be passed through the sample volume because of the absorption of one or more LR wavelengths in the sample volume within sampling accessory 330.
• the non-absorbed LR wavelengths then interact with optically dispersive element 350 to form a dispersed light beam, which separates or spreads, in one direction, the wavelengths present in the LR light exiting sampling accessory 330.
• Optically dispersive element 350 may be, in one aspect of the invention, a ruled diffraction grating having 300 lines (or "grooves") per mm, with a blaze wavelength of 4.0 ⁇ m, for example.
• a grating is manufactured, for example, by SPEX, as model 300 g/mm Holographic Grating.
• the second optically dispersive element may have, for example, 50 grooves per mm, and a blaze wavelength of 9.0mm, to allow two different spectral regions to simultaneously be collected on the FPA, to more efficiently use more of the surface area of the FPA for signal analysis, and to allow for simultaneous analysis of multiple signals.
• the optically dispersive element may be a prism, as shown in Fig. 4.
• Pellin-Broca prism 450 may be used.
• the Pellin-Broca prism may be machined from zinc selenide (ZnSe) in order to minimize the material absorption in these LR spectral ranges, and to ensure adequate optical dispersion as a function of wavelength.
• Figure 5 provides a graph of refractive index dispersion of ZnSe and optical refraction for an exemplary embodiment of the Pellin-Broca prism of Fig. 4.
• Apparatus 400 operates similarly to apparatus 300 shown in FIG. 3 A, however variations in components are optionally present.
• a light coupling means may include LR fiber 410, which may also include a multi-fiber bundle; off-axis parabolic mirror 440; concave mirror 442; and convex mirror 444.
• the light being projected by IR fiber 410 may include light coming from the sample volume being illuminated, or the LR fiber may be used to illuminate the sample volume.
• Focusing optics 360 may be, in this embodiment, a germanium (Ge) condensing lens used to properly project the light emanating from prism 450 onto LR detector 370.
• the parabolic-shaped mirrors are preferable when using an LR fiber, in order to collimate the cone-shaped fiber output light beam.
• the Pellin-Broca prism may also be used with the optical coupling and LR source 310 in FIG. 3, as well as in the fiber optic implementation.
• the ruled diffraction grating may be used with fiber optics, assuming that appropriate measures are taken to collimate the conical beam emanating from the fiber, and to couple the light into the system, and onto the diffraction grating, when used as optically dispersive element 350.
• the Pellin-Broca geometry may provide three benefits: (1) optical dispersion is only a function of the refractive indexes at different wavelengths, thus simplifying the optical design; (2) the two-in-one prism design has a very high angular dispersion efficiency, and the approximate 90° beam folding available allows a compact footprint of the optical system to be achieved; and (3) a Brewster angle incident configuration may be utilized in order to maximize the transmission of light at the ambient/ZnSe interface. The latter is crucial in the LR range where reflection loss is a major concern due to the high refractive index of ZnSe (-2.4).
• a 67.5° Pellin-Broca prism made of ZnSe operating in the "short-side entrance" geometry at approximately the Brewster angle ( ⁇ B of ZnSe ⁇ 67°) will give angular dispersion of about 6° between the 3 and 13 ⁇ m wavelength beams.
• the on-chip spatial separation between the different wavelengths is determined by the focusing optics used, the size of the Pellin-Broca prism, and the f-number of the system.
• a span of between 500 to 1000 cm "1 of the spectral range may be focused onto the FPA horizontally (256, 320, etc. pixels).
• the maximum resolution is about 5 cm “1 .
• a resolution of better than 5 cm "1 is readily achievable for this spectrometer.
• optically dispersive element 350 may be adjustable with respect to an angle of incidence between its surface and incident light which is projected onto the surface. Such an angular adjustment may be used to control the wavelength range, or spectral bandpass that is presented to IR detector 370, discussed below.
• Focusing optics 360 couples light from optically dispersive element 350 into
• LR detector 370 which has a plurality of detection elements arranged at least along a dispersion direction co ⁇ esponding to the direction of the dispersed light beam. Typically, incident light is projected onto more than one row of pixels, and the projected light from the optically dispersive element may cover 20 pixels. LR detector 370 detects the dispersed light beam from optically dispersive element 350, and provides an output, which is subsequently used to determine the IR spectral information of the sample in the sample volume contained in sampling accessory 330.
• LR detector 370 may be an InSb camera sensitive in the 3-5 ⁇ m wavelength range, for example, Merlin Mid model, manufactured by Indigo Systems.
• Such a detector includes a 320 x 256 pixel InSb detector, with 30 micron pixel pitch; a 3.0 - 5.0 micron changeable cold filter; user selectable frame rates of 15, 30 or 60 frame-per-seconds (fps) (minimum); a liquid nitrogen cooled dewar, having a minimum hold time of 4 hours; a noise equivalent temperature difference NE ⁇ T ⁇ 20 mKelvin; user selectable integration times from 10 ⁇ s to 16.6 ms; and corrected non-uniformity ⁇ 0.1%.
• InSb detectors in this range may also be thermoelectrically cooled to enhance portability.
• This particular InSb camera may be controlled via on camera controls or via an RS-232 interface with a vendor supplied Graphical User Interface, or standard Windows ® terminal communications program, or commercially available interfaces such as Universal Serial Bus (USB) or IEEE 1394 standard interface.
• this camera provides an automatic gain control (AGC) algorithm, adjustable detector gain and bias to allow viewing of both high and low brightness scenes, and data outputs which may include NTSC, S- Video, and 12 bit corrected digital video.
• focusing optics 360 may be provided along with LR detector 370; the above-described InSb detector is commercially available with a 25 mm mid-LR lens.
• LR detector 370 may be a microbolometer camera, also manufactured by Indigo Systems as model Merlin Uncooled. This particular camera includes a 320 x 240 pixel microbolometer detector having 51 micron pixel pitch in a 7.5 - 13.5 micron spectral range. User selectable frame rates of 15, 30 or 60 fps (minimum) are available.
• This device in contrast to the LnSb camera, is thermoelectrically (TE) stabilized at 313°K; has a noise equivalent temperature difference NE ⁇ T ⁇ 100 mKelvin; and has user selectable integration times from 1 - 48 ⁇ s.
• This detector array may be controlled in the same manner as for the LnSb array, as discussed above. Similar detector gain controls, and data outputs are available, as in the InSb model.
• MCT (“MCT”) array may be used as LR detector 370, and has improved sensitivity and bandwidth in comparison to the LnSb and microbolometer devices. Presently, such arrays are somewhat difficult to manufacture, and are more expensive than other available LR detectors. Using an available MCT FPA having a maximum frame rate of 6000 Hz, a single beam spectrum may be collected every 170 ⁇ sec, and integration times as low as 10 ⁇ sec are achievable.
• the sensitivity of the InSb FPA is much higher than that of the microbolometer FPA.
• the sensitivity for the InSb FPA identified above is better than a liquid nitrogen-cooled MCT detector commonly used in traditional FTLR.
• the sensitivity of the state-of-the-art microbolometer-based FPA is still about one order of magnitude lower than that of liquid nitrogen-cooled MCT detector.
• sensitivity at the performance level of a liquid nitrogen-cooled MCT detector is not always necessary and, for many applications, it is possible that the lower sensitivity of the microbolometer FPA will not cause any significant efficiency problems in the apparatus.
• the key advantage of using an FPA when compared to single element detector, is the possibility of vertical binning. By adding the signal from a finite height of pixels, SNR can be significantly improved.
• An optical path or light coupling means between the various elements in apparatus 300 may include, in one aspect, standard LR mirrors 340, 341, 342 of various configurations to couple light from LR sources 310, 311 through the sample volume in sampling accessories 320, 321 onto or thru optically dispersive element 350, and onto LR detector 370 through focusing optics 360.
• This configuration could include multiple sampling accessories or polarizers, for example.
• the mirrors may include, for example, 3- inch (-7.6 cm) diameter front surface aluminum mirrors, manufactured by Newport Corporation.
• Other mirror coatings available for use in the LR band may be, for example, copper, and preferably gold.
• Fig. 3C more details of the arrangement shown in Fig. 3B are shown.
• the beam optics may be arranged and adjusted to present the images from each of the samples to a different position on optically dispersive element 350.
• Known methods could be used to address selected rows and/or columns of the FPA, for example.
• the emission from either or both TR light sources 310 and 311 may also be arranged to interact with a background reference environment arranged along the optical path to provide a background reference emission, and the LR FPA detector preferably detects the resulting dispersed background reference light beam on a spatially separated area form the emissions representing the samples.
• the processor preferably receives an output from the FPA including a signal representing the dispersed background reference light beam and, essentially in real time, determines compensated TR spectral information for each of the plurality of samples by compensating for the background reference environment.
• first and second polarizers 335, 336 orthogonally polarized with respect to each other, are placed in the optical path to receive separate LR emissions, which could be, for example, provided by LR light sources 310 and 311.
• the resulting polarized beams both pass through the sample held by sampling accessory 330, for example, and resulting first and second polarized sample emissions are coupled along one or more optical paths to interact with optically dispersive element 350, and are projected onto FPA detector 370.
• a beamsplitter (not shown), in conjunction with the polarizers, may be used to obtain two orthogonally polarized light beams from one LR source beam.
• the first polarized sample emission may orthogonally polarized with respect to the second polarized sample emission. These orthogonally polarized light beams may be used to determine a molecular orientation of a polymer film by comparing the intensities of each of the polarized beams to each other, or to empirical standards.
• the LR FPA detector may preferably detect each of the corresponding plurality of dispersed sample light beams on spatially separated areas of the LR FPA detector.
• the LR FPA detector simultaneously detects the corresponding plurality of dispersed sample light beams, and the at least one output of the FPA determines the LR spectral information for each of the plurality of samples at a same instant in time.
• the FPA preferably comprises LnSb, HgCdTd (MCT), or a microbolometer FPA, and preferably detects light having a wavelength at least in a mid-LR band.
• the LR FPA detector comprises an LR camera.
• Ab LnSb focal plane array (FPA) may be used to detect absorptions in the 3-5 ⁇ m range, while a microbolometer-based FPA may be utilized for the 7-13 ⁇ m range.
• a MCT array, or other InSb or other type of array having a wider or different spectral response may be used.
• the at least one output from the LR FPA detector includes a plurality of summed pixel outputs at each of a plurality of wavelengths present in the dispersed light beam. The plurality of summed pixel outputs at one of the plurality of wavelengths improves a signal-to-noise-ratio of a signal representing an intensity of said one of the plurality of wavelengths.
• the LR FPA detector may be partitioned into multiple segments each containing a different subset of the multiple pixels. Each of the corresponding plurality of dispersed light beams are preferably projected onto an associated one of the multiple segments.
• the "partitioning" of the LR FPA is not necessarily intended to imply an actual physical partitioning realized in hardware, per se, but may be implemented using known techniques for addressing particular rows and columns of pixels on the LR FPA using a relatively simple software control interface between the processor and the LR FPA.
• the corresponding plurality of dispersed sample light beams are preferably projected onto the LR FPA detector such that a row direction on the LR FPA detector is essentially aligned with a dispersion direction of said each of the corresponding plurality of dispersed sample light beams.
• Each column of the focal plane array, within each of the multiple segments, corresponds to a particular wavelength of light contained in the plurality of dispersed sample light beams.
• an output from one pixel in each of a plurality of rows may be added together along one column of the focal plane array to improve a signal-to-noise-ratio of a signal representing an intensity of an associated wavelength of light.
• dispersed sample light beams associated with different spatial sections of one of the plurality of samples are preferably projected onto two or more of the multiple segments. Different wavelengths may be represented within at least two of the multiple segments, whether imaging different spatial sections of one sample, or imaging different samples in the multiple segments.
• At least one of the plurality of samples preferably includes a background target containing an analyte.
• the analyte may be selected to react to a specific type of biological agent to produce an LR absorption change in the background target.
• the analyte may be a bio-specific reagent reactive to one or more biohazardous materials, for example, a virus or bacteria. Further, an audible or visual alarm, or both, may be activated when the bio-specific reagent reacts to any biohazardous materials.
• the at least one sample holder or accessory includes a plurality of sampling accessories, each of said plurality of sampling accessories positioning a different sample volume in the optical path.
• the apparatus preferably simultaneously determines LR spectral information for each of the different sample volumes.
• the sample holder is preferably configured to provide an optical path for each of the plurality of samples that is suitable for detection of an LR absorption phenomenon within the optical path.
• a plurality of optically dispersive elements 350 (not shown) is preferably provided for forming a plurality of dispersed light beams, each corresponding to a different sample.
• Each of the plurality of dispersed light beams may be projected onto a different spatial area on the LR FPA detector 370.
• a display for displaying an LR spectrograph for one or more of the plurality of samples, and means for controlling the LR FPA detector and the display are preferably provided.
• the means for controlling the LR FPA detector and the display preferably includes at least a processor or a personal computer.
• LR light source 310, 311 may be transmitted through each of the plurality of samples along the optical path.
• the emission from the LR light source may be reflected from each of the plurality of samples along the optical path.
• the optical path may include the use of an optical fiber or optical fiber bundle, particularly multimode LR optical fibers, such as, for example, fiber model Cl-500 manufactured by Amorphous Materials, Inc.
• multimode LR optical fibers such as, for example, fiber model Cl-500 manufactured by Amorphous Materials, Inc.
• Different sample types and sampling geometry may advantageously allow a mid-LR optical fiber to be incorporated between the source and dispersing element to deliver the LR source to the sample volume, and to provide an optical path for the TR light after absorption in the sample volume to the dispersive element.
• Optical fibers with loss below 1 dB/m in the mid-IR range are commercially available. These multimode fibers offer features such as flexibility and ease-of-use as found in their fiber counterparts in the visible and near-LR range. The thermal and mechanical properties of these optical materials have been improved dramatically over the past decade.
• Processor 480 may be a special purpose computer adapted specifically for IR spectral processing, and may be implemented in so-called “firmware” or integrated circuits such as a custom application specific integrated circuit (ASIC), or may be a common personal computer (PC). Processor 480 preferably provides control software/hardware for TR detector 470.
• Processor 380 may be implemented as a dedicated LR image acquisition station which includes a 500 MHz Pentium ® III PC, 256 MB RAM, 12 GB hard drive, Windows ® NT 4.0 operating system, LR camera digital interface cable (10 ft, or -3 m), high speed 16 bit frame grabber, camera interface software, and image analysis software based on Image Pro® 4.0 or equal.
• LR image acquisition station which includes a 500 MHz Pentium ® III PC, 256 MB RAM, 12 GB hard drive, Windows ® NT 4.0 operating system, LR camera digital interface cable (10 ft, or -3 m), high speed 16 bit frame grabber, camera interface software, and image analysis software based on Image Pro® 4.0 or equal.
• Such an exemplary package provides a full range of utilities for processing, measuring, analyzing, and outputting images to capture, study, manipulate, and store images and data from the LR camera.
• Display device 390 may be either a standard computer monitor such as a CRT or LCD display, or may be a printing device.
• processor 380 of 480 may be incorporated into a laptop or notebook computer, with an integral LCD display.
• software running on processor 380 or 480 preferably provides a wide variety of features such as real-time histograms; real-time digital filtering; real-time frame averaging, a user definable region-of-interest (ROI); full-featured data display, reduction, analysis capability; and Visual Basic-compatible macro language for automating data collection, analysis, and reporting.
• features such as real-time histograms; real-time digital filtering; real-time frame averaging, a user definable region-of-interest (ROI); full-featured data display, reduction, analysis capability; and Visual Basic-compatible macro language for automating data collection, analysis, and reporting.
• real-time is preferably considered to be less than one second, from initialization, through sampling and analysis, and is even more preferably considered to be less than 500 msec, and is even more preferable to be less than 20 msec.
• This type of response time provides favorable results over the conventional scanning and interferometric techniques.
• real-time detection more preferably means the ability to continuously monitor a process as it happens, where the time domain between collected data sets, or duty cycle is, in general, in the 5-100 ⁇ s range.
• Additional analysis software may operate in processor 380, 480 to analyze the ER spectral information, and to determine one or more specific functional groups found in the sample volume, e.g., fluorocarbons, hydrocarbons, or complex molecular bonds or "signature" functional groups, such as those found in chemical or biological warfare agents. Further, an alarm, either audible or visual, or both may also be activated if a particular signature functional group or chemical composition is determined to be in the sample volume.
• functional groups found in the sample volume e.g., fluorocarbons, hydrocarbons, or complex molecular bonds or "signature" functional groups, such as those found in chemical or biological warfare agents.
• an alarm either audible or visual, or both may also be activated if a particular signature functional group or chemical composition is determined to be in the sample volume.
• apparatus 300, 400 are adjustable to facilitate setup or to provide for optimal data collection, it should be noted that apparatus 300, 400 are capable of determining IR spectral information using no moving parts whatsoever during operation.
• the non-interferometric apparatus of the first embodiment is operated to determine an LR spectrum of a sample in a sample volume by providing an LR source; positioning the sample volume in the optical path; passing at least a portion of an emission of the LR source through the sample volume and into the optical path; optically dispersing at least a portion of an emission of the LR source to form a dispersed TR light beam; detecting the dispersed LR light beam using the plurality of detectors; and non-interferometrically determining the LR spectrum of the sample by evaluating an output from the plurality of detectors.
• a two-dimensional detector array such as a FPA, for example, is operated, wherein each column of detectors represents a wavelength contained within the dispersed LR light beam, and at least two rows of detector elements are used to improve a SNR of the detected signal.
• ER sources 310, 311 Before the apparatus may reliably be used, ER sources 310, 311 must be calibrated, or preferably at least the spectral intensity across the band of interest must be known, in order to compensate for possible non-uniform source intensity.
• the source calibration process included a serial process of collecting the background power spectrum without a sample volume in the optical; collecting the sample power spectrum; and then dividing (or forming a ratio of) the sample power spectrum by the background power spectrum to determine the sample intensity/background intensity, or transmission, for every frequency position reported by the apparatus.
• the data is further processed by a logarithmic operation, i.e., determining the absorbance spectrum (ABS), as
• ABS cc -logio sample/background.
• source and environment calibration are preferably carried out simultaneously with sample emission detection.
• Processors 380, 480 then compensate the sample measurements essentially in realtime, using the source and environment calibration data.
• the disclosed apparatus and method may be used in industrial or environmental process monitoring to measure a thickness of a solid or liquid film or coating on another solid or liquid, for example.
• ABS absorbance spectrum
• ABS A x B x C
• A is the absorption coefficient of the absorbing functional groups present in the sample
• B is the path length within the sample (thickness)
• C is the concentration of the functional groups.
• Concentration and thickness measurements can be made using a standard sample with known concentration C and known thickness B, to calculate the absorption coefficient A for any vibrational band shown by that sample. Once A is known for the absorption band, one then can use Beer's Law to measure either the concentration or the thickness.
• the polarization of infrared light is often accomplished with the use of a gold wire polarizer.
• This optical device may be composed of, for example, finely separated gold wires arranged in parallel on a LR transparent substrate, such as ZnS.
• a method further includes adjusting an optical dispersion of the plurality of sample emissions to control a range of wavelengths in the plurality of dispersed sample beams.
• an angle of incidence on either optically dispersive element 350, e.g., a grating, or prism 450, e.g., a Pellin-Broca prism is adjusted to vary the range of wavelengths presented to the ER FPA 370, 470.
• the method may further include increasing a signal-to-noise-ratio by co- adding a plurality of pixel outputs in said each column of pixels in one of the spatially separated areas.
• the method includes simultaneously evaluating a reference spectrum of an environmental background; and correcting the LR spectrum of each of the plurality of sample to account for the reference spectrum of the environmental background.
• the method may also include simultaneously evaluating a spectrum of the LR source; and correcting the ER spectrum of each of the plurality of sample to account for the spectrum of the LR source.
• the method may include processing the LR spectrum of each of the plurality of sample emissions to identify one or more signature functional groups in the plurality of sample volumes; and enabling an alarm if one or more signature functional groups, for example, a chemical or biological warfare agent, are found in any one of the plurality of sample emissions.
• one or more signature functional groups for example, a chemical or biological warfare agent
• the method may include providing a background target having a bio-specific reagent thereon; and reacting the bio-specific reagent with a sample volume containing said one or more signature functional groups.
• a method further includes maintaining the broadband light source, the optically dispersive element, and the two-dimensional LR detector array relatively motionless at least with respect to each other at least during said steps of projecting, interacting, coupling, forming, and optically coupling steps.
• the optical coupling step may include fiber optic coupling of the sample light emissions, and/or the projecting step may include fiber optical coupling a portion of the emission of the broadband light source into the plurality of sample volumes.
• the method may further include determining, from the TR absorption spectrum of one or more of the plurality of samples, at least one physical attribute of the one or more of the plurality of samples, wherein at least one physical attribute is continuously determined essentially in real-time.
• the physical attribute may include a molecular orientation of one of the plurality of samples, for example, which is accomplished, at least in part, by comparing two orthogonally polarized sample emissions associated with said one of the plurality of samples.
• the physical attribute may also include measuring a thickness of a film in real-time, in particular, a monolayer polymer film.
• each ofthe plurality of LR light sources 310, 311 may have a different intensity and, in another aspect ofthe invention, one or more ofthe optical paths may include a polarizing element.
• the processing means may be used to ascertain a molecular orientation of a monolayer, including a polymer monolayer, from ER spectral information determined from the different spatial areas on the TR FPA, particularly where orthogonally polarized sample emissions are evaluated.
• the method further includes computing a refractive index and an absorption coefficient ofthe film material.
• the substrate may include a dielectric substrate having known optical properties, as used in semiconductor processing, for example.
• the monolayer film also may be adsorbed on the substrate.
• the method may further include projecting the LR light source onto a surface ofthe substrate at a plurality of non-perpendicular angles of incidence; and determining the angle of refraction within the film material by measuring the angle of rotation ofthe mirror for each ofthe plurality of non-perpendicular angles of incidence.
• polarized ER radiation may be projected through the film material and the substrate; directionally specific angles of refraction within the film material may be determined; and the directionally specific complex indices of refraction ofthe film material may be computed.
• a molecular orientation of at least one molecular group in the film material may be determined.
• a thin Teflon bar ⁇ er may preferably be inserted in Langmuir film balance, so that two separate troughs are created, as seen in Fig. 6.
• the smaller trough may be used as a reference trough, while the larger tough may be used as a sample trough.
• the center of a relatively wide collimated infrared beam (e.g., 4 or 5 cm) may be reflected at the point where the two troughs are separated, i.e., at the thin Teflon ® barrier.
• polarized infrared spectra may readily be obtained by measuring the sample, e.g., a film, through polarizing elements using transmission or reflection ofthe LR beam, and then immediately directing the beam through a dispersive element.
• an emission may be split in a beam splitter (not shown), and then each split beam could be passed through two different, orthogonally polarized elements in respective optical paths, and through the sample or samples, to determine polarization- specific information.
• time-resolved measurements in the sub-millisecond time regime may be obtained during the recording of a pressure area isotherm for polymers of interest by using signal averaging.
• the PAIR instrument's multiple spectral image capability allows higher intensity sources to be used to collect both s-polarized and p-polarized spectra (reflectivity is significantly higher for s-polarized radiation than for p-polarized radiation) of monolayers during compression, thereby providing a continuous molecular picture ofthe development of order and orientation at all points along the isotherm.
• molecular orientations of thin films using polarized infrared spectra ofthe thin films may be determined. There are known techniques for doing so, however, for LR external reflection measurements from dielectric substrates, a knowledge ofthe anisotropic ER optical constants (e.g., index of refraction and extinction coefficient) is required. This information is often difficult to obtain.
• anisotropic ER optical constants e.g., index of refraction and extinction coefficient
• the PALR spectrograph ofthe present invention may be applied to determine the anisotropic optical constants ofthe thin films.
• a monolayer film adsorbed on a dielectric substrate can conveniently be considered as a stratified three-phase system, such as that shown schematically in Fig. 8.
• the film thickness is represented by d, which may be as small as one molecule, i.e., a monolayer.
• a PALR spectrograph can be used to determine n 2 and k 2 , i.e., the optical constants ofthe monolayer film.
• Film thickness is easily determined with a known visible ellipsometer, while fli (air) and n 3 (a typical dielectric substrate, for example) have known values.
• Figure 9 shows reflection and refraction of infrared radiation that is incident on a dielectric substrate, where E is the intensity ofthe reflected radiation (at a given frequency); E' is the intensity ofthe transmitted (refracted) radiation; ⁇ i is the angle of reflection, which is equal to the angle of incidence and is easily measured, and ⁇ 2 is the angle of refraction.
• E the intensity ofthe reflected radiation (at a given frequency)
• E' the intensity ofthe transmitted (refracted) radiation
• ⁇ i the angle of reflection, which is equal to the angle of incidence and is easily measured
• ⁇ 2 is the angle of refraction.
• a clean dielectric substrate is placed horizontally in the sample position (see Fig. 9).
• An arbitrary ER light source may be transmitted through the dielectric substrate at a known angle relative to the surface normal, where it then strikes the FPA at a specific, known area, "A" (not shown).
• the same dielectric substrate, now with an adsorbed monolayer film on it, is then placed in the sample position.
• the plane mirror is then rotated until light strikes the same area, "A", ofthe FPA.
• the optical constants ofthe monolayer film (n 2 and k 2 ) can be determined using the Fresnel equations and a known iterative procedure. Using multiple angles of incidence ⁇ i improves the accuracy of these determinations.
• the initially polarized incident FTLR light beam (via a wire grid polarizer, for example) undergoes a fast modulation between two orthogonal polarization directions via a photoelastic modulator.
• the detected signal passes through a two-channel electronic system, and is mathematically processed to give a differential reflectivity spectrum.
• the PM-LRRAS differential reflectivity spectrum signal is essentially devoid of all polarization-independent signals, such as strong water vapor absorptions which are isotropic, instrumental drifts, and fluctuations in signal strength.
• this approach still relies upon the moving part and calculation-intensive Fourier Transform approach, which this invention specifically disfavors.
• a non-interferometric PALR arrangement for Planar Array Infrared Reflectance- Absorbance Spectroscopy (PA-LRRAS) for measuring an orientation of a thin film on a substrate includes an LR source; two fixed, orthogonal polarizers 335, 336; a PALR detector as previously described and illustrated, including a processor and a display.
• PA-LRRAS Planar Array Infrared Reflectance- Absorbance Spectroscopy
• the orthogonally polarized beams are reflected from the thin film, and detected by the PALR detector.
• the processor calculates a differential reflectivity spectrum based upon analysis ofthe two orthogonally polarized signals received by the PALR detector.
• the differential spectrum is substantially free of any polarization-independent signals including isotropic water vapor absorptions, instrumental drifts, and signal fluctuations, because these effects are essentially canceled out by the differential technique.
• the differential reflectivity spectrum may be further used to determine a molecular orientation ofthe thin film.
• the polarization modulator may be a photoelastic modulator, and the FPA could be an InSb FPA, an MCT FPA, or a microbolometer FPA, for example.
• the application and method ofthe disclosed invention has wide applicability to a variety of industrial and environmental processes, as discussed above, including measuring characteristics of thin films, including optical constants.
• Some further applications include a method to measure the thickness, the chemical structure and orientation of coatings (solid, liquid, chemically bound, physically adsorbed) on solid surfaces, including but not limited to semiconductors, metals and dielectrics.
• coatings solid, liquid, chemically bound, physically adsorbed
• solid surfaces including but not limited to semiconductors, metals and dielectrics.
• subtle differences in the processed materials on a molecular level can determine the success or failure of a specific procedure.
• Molecular parameters such as crystalline order, chain orientation, and hydrogen bonding strength can have important effects on the functionality of the final devices.
• liquid crystal displays used in notebook computers rely on the chain orientation ofthe polymer coating used on the glass templates to define the "off orientation ofthe liquid crystal molecules, which act as a light modulator.
• Process methods such as scanning probe microscopy and x-ray diffraction, for example, can be destructive in nature, requiring long data collection times and removal of samples from the production line. Consequently, the real-time statistics needed for a successful on-line process monitoring method cannot be achieved with conventional techniques.
• the disclosed apparatus and method can non-destructively monitor processes in real-time, for example, information about chain orientation of large area samples can be obtained in situ after the buffing process is completed.
• An environmental application of LR spectroscopy in an aqueous environment could be detection and measurement of oil or other contaminants on the surface using reflected LR energy to determine the presence or absence of specific functional groups.
• the IR spectrometer is highly mobile, it may be used as a water pollution monitor, capable of operation in the field as discussed above.
• the spectral coverage ofthe invention will detect the spectral features in the fingerprint region for most aromatic pollutants. Since the IR bands (1600-1750 cm “1 ) assignable to water will not interfere with the pollutants' signal in this spectral range, bulk analysis of wastewater in the field is also possible with this instrument.
• transition moments ofthe CH 2 rocking components at 730 and 720 cm “1 are parallel to the "a” and “b” axes ofthe unit cell ("c" is along the chain axis) respectively, it should also be possible to determine the extent of biaxial orientation which is introduced in the drawing process by following the relative intensities of the 730 and 720 cm “1 bands in the polarized LR beam during processing.
• both sets of bands are highly polarized pe ⁇ endicular to the polymer chain axis, their intensity can also be used to provide information on axial orientation related to the direction of mechanical deformation.
• CH stretching vibrations located at 2920 cm “1 (asymmetric CH 2 stretch) and 2850 cm “1 (symmetric CH 2 stretch) are strongly polarized out ofthe plane ofthe carbon backbone and in the plane ofthe carbon backbone respectively. Hence these vibrations can also be used to determine the extent of "a” and "b" axis orientation in biaxially oriented films.
• PEN poly(ethylenenaphthalate)
• Further industrial applications ofthe disclosed apparatus include a method to measure and detect the thickness, either in transmission or reflection, the chemical structure and orientation of coatings/films (solid, liquid, chemically bound, physically adsorbed) on liquid surfaces, including but not limited to water, oil and other solvents.
• discussion of aspects ofthe present invention have been directed to determining FR spectral information, the method and system ofthe present invention is not limited merely to such a na ⁇ ow implementation.
• the present invention may also be applicable to the above-discussed industrial and environmental processes, and may further be inco ⁇ orated into a control system in a batch production line to control one or more physical attributes, such as a polymer film thickness, or in semiconductor processing, for example, while measuring multiple samples simultaneously, and while compensating for background emissions.
• a control system in a batch production line to control one or more physical attributes, such as a polymer film thickness, or in semiconductor processing, for example, while measuring multiple samples simultaneously, and while compensating for background emissions.

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