This application claims the benefit of nonprovisional patent application Ser. No. 16/997,248 filed Aug. 18, 2020, by the present inventor.
The invention is in the technical field of reflectance spectroscopy and substance-on-surface identification.
In the area of reflectance spectroscopy, interference effects from films of unknown refractive index and thickness cause ambiguities in substance-on-surface identification. This presents a problem not in the laboratory, but in the field, where the thickness of the film to be identified is not controlled, and nothing at all is known about the film to begin with. A complication is that any illuminating beam incident on the film is immediately converted into multiple reflected and refracted beams. An essential first step in identifying the substance is selecting a single dyad from the host of multiply refracted and reflected derivative beams and measuring their separation, not in a controlled laboratory environment, but in the uncontrolled, unforgiving field. This patent application presents a method to accomplish this.
As exemplified by one embodiment, this invention is a method of using a moveable variable-aperture apparatus and a lens and detector to select a chosen dyad from a multiplicity of parallel coherent, frequency-modulated light beams, and to measure their separation.
In one embodiment, in an aspect, a method of using a moveable, variable-aperture apparatus in conjunction with a lens and a detector to admit only two beams from a multiplicity of parallel beams of frequency-modulated coherent light via the following steps: pre-setting said moveable, variable-aperture apparatus's aperture to the known width of a single beam of light, then positioning said moveable, variable-aperture apparatus until the light which passes its aperture is of maximum intensity and zero beat frequency, then leaving said moveable, variable-aperture apparatus in place but opening the aperture to the minimum width with which the light passing through its aperture attains maximum intensity with non-zero beat frequency, and thus admitting only two beams of light from the multiplicity of parallel beams.
In another embodiment, in an aspect, a method of using a moveable, variable-aperture apparatus to measure the separation between two parallel beams of light, comprising the method of the previously-described embodiment and the measuring q, the width of the aperture upon completion of the method of the previously-described embodiment, then subtracting w, the known beamwidth, from q, the aperture width, to obtain s, the separation of the beams' central axes, using the equation s=q−w.
In another embodiment, in an aspect, a method of using a moveable, variable-aperture apparatus to measure an alternative separation between two parallel beams of light, comprising the method described in the embodiment discussed two paragraphs above this paragraph, and then measuring q, the width of the aperture upon completion of said method and subtracting twice the known beamwidth w from the aperture width q, to obtain u, the separation of the beams' outer envelopes, using the equation u=q−2w.
In the drawings, closely related figures have the same number but different alphabetic suffixes.
To illustrate the method, an embodiment of the aperture apparatus and accessories that can be used for implementation is described. In the moveable variable-aperture apparatus of
The widths of the parallel coherent beams 8, 9 and 10 will be known from the optical system that produced them, but generally their separations are not necessarily known. For example, the beam separations could be unknown if beams 8, 9 and 10 resulted from multiple refractions and reflections of an original beam that was incident on a dielectric slab. Parallel coherent beams 8, 9 and 10 are all frequency-modulated.
Operation—
The method of using the moveable variable-aperture apparatus and the lens and detector is as follows. The MVA apparatus is first opened so that its aperture is the known width of a single beam, then the apparatus is positioned so that the light which passes through the aperture is of maximum intensity and zero beat frequency, being a single beam (
The foregoing discussions can be summarised with the following algorithm.
Additional embodiments of the aperture apparatus and its accessories are possible. For instance, the converging lens 6 can be replaced by a converging mirror, with the detector 7 placed in front of the mirror rather than behind it.
Advantages
From the foregoing description, a number of advantages of my method become evident:
The main reference for this invention is
Accordingly, the reader will see that the method described can easily select any chosen dyad of parallel beams from a multitude of frequency-modulated parallel beams and measure their separation in two ways.
This method is able to do its stated tasks in an uncontrolled, non-laboratory setting. This precise ability is crucial to measuring refractive index and thickness of dielectric films in the field. In turn, the field measurement of refractive index and film thickness are critical to the unambiguous identification of substances on surfaces by their diffuse infrared reflectance spectra.
Although the description above contains many specificities, these should not be construed as limiting the scope of the embodiments but as merely providing illustrations of some of several embodiments. For example, the converging lens can be replaced by a converging mirror, and the detector placed off-axis in front of the mirror rather than on-axis behind the lens. The scope of the embodiments should be determined by the appended claims and their legal equivalents, rather than by the examples given.
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Entry |
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Fauconier, Richard, Mandoye Ndoye, and Webert Montlouis. “Optical fundamentals of an adaptive substance-on-surface chemical recognizer.” Electro-Optical and Infrared Systems: Technology and Applications XIV. vol. 10433. International Society for Optics and Photonics, 2017. (Year: 2017). |
Richard Fauconier, “Feedback control method for limiting interfering Gaussian beams in a bistatic substance-onsurface chemical recognizer”, SPIE Security and Defence 2019 Proceedings, vol. 11159, Electro-Optical and Infrared Systems: Technology and Applications XVI, 111590T, Strasbourg, France, Oct. 9, 2019. |
Number | Date | Country | |
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Parent | 16997248 | Aug 2020 | US |
Child | 17155402 | US |