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
  • G01J3/28—Investigating the spectrum
  • G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
• • 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
  • G01J3/44—Raman spectrometry; Scattering spectrometry ; Fluorescence 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
  • 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 determining an IR spectrum of a sample material. More particularly, the disclosed invention relates to spectroscopically determining the IR spectrum of a sample using an apparatus and method that operate in real-time, 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.
• 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.
• spectroscopic measurement 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 1 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.
• Modern applications of spectroscopy have generalized the meaning of "light” to include the entire range or spectrum of electromagnetic radiation, which extends from gamma- and x-rays, through ultraviolet, visible, and infrared light, to microwaves and radio waves.
• IR infrared
• UV ultraviolet
• IR spectroscopy examines vibrational transitions within a single electronic state of a molecule, and is not concerned with specific 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 IR radiation, except homonuclear diatomic molecules, e.g., O2, H 2 , N2, CI2, F2, or noble gases.
• homonuclear diatomic molecules e.g., O2, H 2 , N2, CI2, F2, or noble gases.
• IR typically covers the range of the electromagnetic spectrum between 0.78 and 1000 ⁇ m.
• 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.
• the IR range is sometimes further delineated by three regions having the wavelength and corresponding wavenumber ranges indicated:
• the vibrations or rotations within the molecule must cause a net change in the dipole moment of the molecule.
• the alternating electric field of the incident IR radiation interacts with fluctuations in the dipole moment of the molecule and, if the frequency of the radiation matches the vibrational frequency of the molecule, then radiation will be absorbed, causing a reduction in the IR band intensity due to the molecular vibration.
• 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 IR 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.
• an appropriate wavelength can be directed at the sample being analyzed, and then the amount of energy absorbed by the sample can be measured.
• the intensity of the absorption is related to the concentration of the component. The more energy that is absorbed, the more of that particular functional group exists in the sample. Results can therefore be numerically quantified. Further, the absence of an absorption band in a sample can often provide equally useful information.
• Intensity and frequency of sample absorption are depicted in a two-dimensional plot called a spectrum. Intensity is generally reported in terms of absorbance, the amount of light absorbed by a sample, or percent transmittance, the amount of light that passes through it. In IR spectros- copy, frequency is usually reported in terms of wavenumbers, as defined above.
• Infrared 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 IR. By scanning the optically dispersive element, spectral information may be obtained at different wavelengths.
• a light source e.g., the sun
• optically dispersive element such as a prism
• detector sensitive to IR By scanning the optically dispersive element, spectral information may be obtained at different wavelengths.
• 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.
• FTIR interferometer More recently, a Michelson interferometer has been used to generate a so-called interferogram in the IR spectrum, which later is subjected to Fourier transform processing such as a fast Fourier transform (FFT) to yield the final spectrum. In the IR range, such spectrometers are called FTIR interferometers, and the first commercially available appeared in the mid 1960's. A representation of an FTIR interferometer is provided in Fig. 1. [0016] The key components of FTIR interferometer 100 are IR source
• FTIR 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.
• IR detector 160 is used to detect this interference pattern.
• the detected interference pattern 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.
• the invention of FT spectroscopy has proven to be one of the most important advances in modern instrumentation development in the 20th Century.
• Optical spectroscopy utilizing the interference of light has made fast, sensitive detection of molecular vibration/ rotation possible due to the large throughput and multiplex advantages provided by FT instrumentation.
• NMR Nuclear Magnetic Resonance
• mass spectroscopy where high-resolution spectra are required, FT instrumentation has also prevailed as the state of the art.
• 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 is workable, the signal-to-noise-ratios (SNR) obtainable often requires substantial signal averaging of multiple interferograms, thus making FTIR systems inherently slow, with reduced speed and lower reliability resulting from the numerous moving parts of these systems.
• SNR signal-to-noise-ratios
• 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 1 / 1000 th cm.- 1 , depending on the amount of possible movement of the mirror, or the pathlength 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.
• IR spectroscopy based on dispersion became obsolete in most analytical applications in the late 1970'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 IR range of the spectrum. Today, however, array detectors in the visible and near-IR range are widely available for area detection of photons.
• CCD Charge-coupled-devices
• QE quan- turn efficiency
• the present invention solves many of the aforementioned problems of providing a robust, high-resolution and sensitive apparatus and method for determining an IR spectrum of a sample material, without the use of moving parts, or calculation-intensive Fourier Transform interfer- ometric techniques.
• a first embodiment of the present invention includes an apparatus for determining an IR spectrum of a sample material based upon IR FPA technology to capture the IR spectral information, without utilizing a scanning mechanism, or any moving parts, and without the use of Fourier Transform signal processing.
• An IR source is passed through a sample volume, where at least some of the IR energy is absorbed in the sample volume.
• the resulting IR signal is optically dispersed to spread the IR light into its respective wavelength components, and projected onto an IR detector having a plurality of detection elements.
• the detector output is further processed for display and analysis without interferometric techniques.
• one or more optical fibers are used to couple the IR source through a sample volume, and into an optically dispersive element, and also into an IR detector.
• Such an embodiment may be used, for example, in remote-sensing applications, where the phenomena being evaluated are remotely located from the apparatus, particularly the IR detector.
• the sample volume to be analyzed may be hundreds of meters in the air.
• Fiber optical cabling may be used, as may telescopic optics to bring the experiment to the sensor.
• an InSb focal plane array (FPA) is used to detect absorptions in the 3-5 ⁇ m range and, in a second aspect of the first embodiment, a microbolometer-based FPA is utilized for the 7- 13 ⁇ m range.
• FPA InSb focal plane array
• MCT HgCdTd
• MCT HgCdTd
• Signals from the samples can be collected by either of two methods. Signal collection by direct lens coupling may be used by coupling the signals into the spectrometer through an aperture. Alternatively, the coupling is also accomplished through the use of mid-IR optical fibers. [0042] Use of optical fibers provide 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. [0043] The apparatus and method of the present invention does 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.
• the method 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.
• FIG. 1 provides a representation of a conventional FTIR interferometer
• FIG. 2 provides two different schemes used for conventional in- terferometry based on Fourier Transform, but which do not require moving parts to generate a difference in optical path length;
• FIG.3 depicts one embodiment of the present invention in which non-interferometric IR spectroscopy is accomplished using no moving parts;
• FIG. 4 provides another embodiment using a Pellin-Broca prism as the optically dispersive element, and which shows IR 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 an exemplary embodiment of the Pellin-Broca prism of Fig. 4;
• FIG. 6 demonstrates representative noise and signal averaging achievable by the disclosed invention.
• FIG. 7 compares results of the disclosed invention with a conventional FTIR interferometer.
• Apparatus 300 includes an IR light source 310, which may be any common IR light source, including, for example, tungsten lamps, Nernst glowers, or glowbars or, in some applications, IR radiation from the sun may be used.
• the IR source may be a IR Emitter with ZnSe window, manufactured by Cal-Sensors, for example.
• IR source 310 has a "flat" or uniform intensity across the IR spectrum, or at least a portion of the IR spectrum. However, if IR 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 the sample volume, which contains a sample to be analyzed, in the optical path.
• Sampling accessory 320 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 IR source 310, or it may comprise a more elaborate sampling volume arrangement known and used for sampling gases.
• Gases, which have a lower density than solids or liquids, may require such a more elaborate sampling accessory having a set of mirrors or other suitable arrangement (not shown) to provide for multiple passes of the IR source through the sample volume. Such multiple passes are useful in ensuring that sufficient optical density is achieved for the IR 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 (not shown) that may be used, along with appropriate beam splitting optics, to pass a portion of an emission from IR source 310 through each of the plurality of sampling accessories.
• Optically dispersive element 350 receives a portion of an emission from IR light source 310 that is passed through the sample volume.
• the entire IR spectrum, representative of IR source 310 may not be passed through the sample volume because of the absorption of one or more IR wavelengths in the sample volume within sampling accessory 330.
• the non- absorbed IR 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 IR light exiting sampling accessory 330.
• Optically dispersive element 350 may be, in one embodiment, a ruled diffraction grating having, for example, 300 lines per mm. Such a grating is manufactured, for example, by SPEX, as model 300 g/mm Holographic Grating.
• 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 IR spectral ranges, and to ensure adequate optical dis- persion as a function of wavelength.
• Fig. 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, however variations in components are optionally present.
• a light coupling means may include IR 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 IR fiber may be used to illuminate the sample volume.
• Focusing optics 370 may be, in this embodiment, a germanium (Ge) condensing lens used to properly project the light emanating from prism 450 onto IR detector 370.
• the parabolic-shaped mirrors are preferable when using an IR 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 IR 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 IR range where reflection loss is a major concern due to the high refractive index of ZnSe (-2.4).
• 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 IR detector 370 which has a plurality of detection elements arranged at least along a dispersion direction corresponding 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.
• IR 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.
• IR 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 IR detector 370; the above- described InSb detector is commercially available with a 25 mm mid-IR lens.
• IR 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 InSb 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.
• TE thermoelectrically
• This detector array may be controlled in the same manner as for the InSb array, as discussed above. Similar detector gain controls, and data outputs are available, as in the InSb model.
• HgCdTe (MCT) arrays show great promise for use as IR detector 370, and have improved sensitivity and bandwidth in comparison to the InSb and microbolometer devices. Presently, such arrays are somewhat difficult to manufacture, and are more expensive than other available IR detectors.
• InSb and microbolometer types of detectors may be cooled thermoelectrically, the sensitivity of the InSb FPA is much higher than that of the microbolometer FPA. As a matter of fact, the sensitivity for the InSb FPA identified above is better than a liquid nitrogen-cooled MCT detector commonly used in traditional FTIR.
• 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 problem 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.
• IR detector 370 has been described in terms of a focal plane array (FPA) configuration, a linear array detector may also be used as IR detector 370.
• a linear array detector having a plurality of detector elements in the one-dimensional array is not capable of taking advantage of several features that a two-dimensional detector array offers. Such advantages are, for example, vertical "binning" or co- adding of detector array pixel outputs to increase a signal-to-noise (SNR) ratio, and multichannel detection capability using different areas of the FPA for multiple sample analysis. These additional features would not be available with a linear array.
• SNR signal-to-noise
• An optical path or light coupling means between the various elements in apparatus 300 may include, in one embodiment, standard IR mirrors 340, 342 of various configurations to couple light from IR source 310, through the sample volume in sampling accessory 320, onto or thru optically dispersive element 330, and onto IR detector 370 through focusing optics 360.
• Such mirrors may be, for example, 3-inch (-7.6 cm) diameter front surface aluminum mirrors, manufactured by Newport Corporation.
• Other mirror coatings available for use in the IR band may be, for example, copper or gold.
• the optical path may include the use of an optical fiber or optical fiber bundle, particularly mul- » timode IR optical fibers, such as, for example, fiber model C 1-500 manufactured by Amorphous Materials, Inc.
• an optical fiber or optical fiber bundle particularly mul- » timode IR optical fibers, such as, for example, fiber model C 1-500 manufactured by Amorphous Materials, Inc.
• Different sample types and sampling geometry may advantageously allow a mid-IR optical fiber to be incorporated between the source and dispersing element to deliver the IR source to the sample volume, and to provide an optical path for the IR 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 mul- timode fibers offer features such as flexibility and ease-of-use as found in their fiber counterparts in the visible and near-IR range. The thermal and mechanical properties of these optical materials have been improved dramatically over the past decade.
• off-axis parabolic mirror 440 is utilized to collect and collimate the signals from either the entrance aperture or an output end of IR fiber 410 or fiber bundle.
• An adjustable aperture 420 may be used to control the size of the coUimated beam, and subsequent condensing optics 442, 444 are used to couple the signal into the prism.
• Processor 380 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 380 preferably provides control software /hardware for IR detector 370.
• “Talon Ultra" Data Acquisition System manufactured by Indigo Systems may be used.
• Processor 380 may be implemented as a dedicated IR image acquisition station which includes a 500 MHz Pentium ® III PC, 256 MB RAM, 12 GB hard drive, Windows ® NT 4.0 operating system, IR 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.
• IR camera digital interface cable (10 ft, or -3 m) IR camera digital interface cable (10 ft, or -3 m)
• High speed 16 bit frame grabber camera interface software
• image analysis software based on Image Pro® 4.0 or equal.
• 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 may be incorporated into a laptop or notebook computer, with an integral LCD display.
• 380 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 interferomet- ric 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 ⁇ sec range.
• Additional analysis software may operate in processor 380 to analyze the IR 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 is 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 IR spectrum of a sample in a sample volume by providing an IR source; positioning the sample volume in the optical path; passing at least a portion of an emission of the IR source through the sample volume and into the optical path; optically dispersing the at least a portion of an emission of the IR source to form a dispersed IR light beam; detecting the dispersed IR light beam using the plurality of detectors; and non- interferometrically determining the IR 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 IR light beam, and at least two rows of detector elements are used to improve a SNR of the detected signal.
• IR source 310 Before the apparatus may reliably be used, IR source 310 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 includes 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 -logio (sample/ background).
• ABS absorbance spectrum
• ABS A x B x C, where A is the absorption coefficient of the absorbing functional groups present in the sample; B is the path length within the sample (thickness), and C is the concentration of the functional groups. This quantitative relation is widely known as "Beer's Law”.
• 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. [0091] For example, in a film processing line, if the material formulation is held constant, then the corresponding C and A values are also constant. In this case, one can use the disclosed invention to monitor the film thickness, since the absorbance level is directly proportional to B.
• the concentration of the gaseous species can be measured with the disclosed invention since A (a known species) and B (a fixed chamber size) are held constant, leaving the concentration to be determined as being directly proportional to the measured absorbance.
• A a known species
• B a fixed chamber size
• the polarization of infrared light is often accomplished with the use of a gold wire polarizer.
• This optical device may be composed of, for ex- ample, finely separated gold wires arranged in parallel on a IR transparent substrate, such as ZnS.
• the application and method of the disclosed invention has wide applicability to a variety of industrial and environmental processes.
• Some of the 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.
• IR spectroscopy in an aqueous environment, for example on a lake, river, or on the ocean could be detection and measurement of oil or other contaminants on the surface using reflected IR energy to determine the presence or absence of specific functional groups.
• 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 range offered in the disclosed spectrometer will cover the spectral features in the fingerprint region for most of the aromatic pollutants.
• IR spectroscopy on thin films. Many of the optical, mechanical and aging properties of polymers are a direct function of the order, orientation, and morphological development, which occurs during processing. Ironically little, if any, understanding exists on the structural development of orientation and order at the time when polymers are formed into thin films. The ability to structurally characterize the nature of polymer chain organization by real-time IR spectroscopic methods would allow the optimization of processing protocols providing eventual control of the desired amount of crystallization and orientation relative to the direction of micro mechanical deformation.
• transition moments of the CH2 rocking components at 730 and 720 cnr 1 are parallel to the "a" and “b" axes of the 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 IR beam during processing.
• both sets of bands are highly polarized perpendicular 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 CH2 stretch) and 2850 cm” 1 (symmetric CH2 stretch) are strongly polarized out of the plane of the carbon backbone and in the plane of the carbon backbone respectively. Hence these vibrations can also be used to determine the extent of "a” and "b" axis orientation in biaxially oriented films.
• IR intensities depend on the change in dipole moment (for a particular vibrational mode), and hence provide a more direct assessment of chain orientation, provided the direction of the orientation of the change in dipole moment is known, relative to the polymer chain axis.
• PE polymer on which to conduct IR spectroscopy.
• PET poly(ethylene terephthalate)
• PEN poly(ethylenenaphthalate)
• Further industrial applications of the 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;
• [00112] A method to measure the thickness, orientation and chemical structure of fluorocarbon materials, including but not limited to films, adsorbed gas, coatings on solid and liquid surfaces;
• a method to measure the thickness, orientation and chemical structure of films electrochemically deposited on solid substrates including but not limited to metals and semiconductors;
• a method to detect orientation in films either statically or “realtime” as they are being processed are representative, but not limiting examples of processing
• a real-time method to measure and detect the chemical species present as a chemical reaction in the gaseous, liquid or solid state occurs;
• a real-time method to measure and detect hazardous materials in the gaseous state including but not limited to fumes in factory, laboratory, mining tunnel, storage room and battlefield;
• a real-time method to monitor processes including but not limited to those involving orientation, crystallization, melting, degradation, deposition and sublimation;
• a monitoring method which can be deployed in environments with high mechanical noises, including but not limited to factory, mine, automobile, aircraft or spacecraft; [00121] A monitoring method which can be deployed with infrared telescopic optics and serve as a remote-sensing platform;
• a monitoring method which can be deployed with infrared microscopic optics and perform real-time infrared microscopic sampling; [00123] A monitoring method, which can be deployed with infrared optical fibers to perform medical endoscopic detection.
• 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 achievable for this spectrometer.
• IR spectra of hexadecane were also obtained using a conventional FTIR instrument using 16 cm" 1 , 8 cm- 1 , and 4 cm" 1 resolution.
• the methyl stretch at 2875 cm- 1 observed in all three spectra, can be used as an indication of the instrument's resolution.
• This weak band is found on the high frequency side of the much stronger symmetric CH2 stretch at 2850 cm 4 ,
• the methyl stretch in the FPA-IR spectrum is less resolved than that in the 4 cm" 1 resolution FTIR spectrum, but more resolved than that in the 8 cm 4 resolution FTIR spectrum.
• the method and system of the present invention is not limited merely to such a narrow implementation.
• the present invention may also be applicable to the above-discussed industrial and environmental processes, and may further be incorporated 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.

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