External/internal optical adapter for FTIR spectrophotometer
First Claim
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1. An adapter for use with an FTIR spectrophotometry system having a light source generating a source light beam of coherent light, said adapter comprisinga sealed housing for receiving the source light beam directed along a propagation path;
- an optical system within the housing including a single moveable beamsplitter having first and second reflecting surfaces, each coated with a reflecting layer, said beamsplitter for splitting the source light beam into;
(1) a reference beam reflected by the first reflecting surface to form a first linear path different from the source path, and(2) a sample beam reflected by the second reflecting surface to form a second linear path different from the source path and different from the first linear path,wherein the beamsplitter and its first and second reflecting surfaces are moveable together in a direction perpendicular to the propagation path of the source beam between the first and second linear paths to minimize source noise and to minimize a centerburst of a waveform of an interferogram of the reference beam and the sample beam;
a reference cell within the housing, said reference cell including a reference for interacting with the reference beam wherein said interacting yields an output reference beam having a direction;
a reference light detector for detecting at least a portion of the output reference beam based on the direction of the output reference beam and generating a reference signal representative of the detected light;
a sample cell within the housing, said sample cell including a sample for interacting with the sample beam wherein said interacting yields an output sample beam having a direction;
a sample light detector for detecting at least a portion of the output sample beam based on the direction of the output sample beam and generating a sample signal representative of the detected light;
a detector circuit for producing a difference signal proportional to the difference between the reference signal and the sample signal; and
a processor configured to determine a spectrum of the sample based on the difference signal.
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Abstract
A Fourier Transfer Infrared (FTIR) spectrophotometer having reduced baseline noise. The system and method include internal or external optical adapters having a moveable beamsplitter for splitting the source light beam into a reference beam and a sample beam, and may include a variable bandpass filter, variable preamplifier and reversed biased photodiodes.
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Citations
27 Claims
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1. An adapter for use with an FTIR spectrophotometry system having a light source generating a source light beam of coherent light, said adapter comprising
a sealed housing for receiving the source light beam directed along a propagation path; -
an optical system within the housing including a single moveable beamsplitter having first and second reflecting surfaces, each coated with a reflecting layer, said beamsplitter for splitting the source light beam into; (1) a reference beam reflected by the first reflecting surface to form a first linear path different from the source path, and (2) a sample beam reflected by the second reflecting surface to form a second linear path different from the source path and different from the first linear path, wherein the beamsplitter and its first and second reflecting surfaces are moveable together in a direction perpendicular to the propagation path of the source beam between the first and second linear paths to minimize source noise and to minimize a centerburst of a waveform of an interferogram of the reference beam and the sample beam; a reference cell within the housing, said reference cell including a reference for interacting with the reference beam wherein said interacting yields an output reference beam having a direction; a reference light detector for detecting at least a portion of the output reference beam based on the direction of the output reference beam and generating a reference signal representative of the detected light; a sample cell within the housing, said sample cell including a sample for interacting with the sample beam wherein said interacting yields an output sample beam having a direction; a sample light detector for detecting at least a portion of the output sample beam based on the direction of the output sample beam and generating a sample signal representative of the detected light; a detector circuit for producing a difference signal proportional to the difference between the reference signal and the sample signal; and a processor configured to determine a spectrum of the sample based on the difference signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of determining an optical spectrum for a sample substance relative to a reference substance, said method for use with a spectrophotometry system having a light source generating a source light beam of coherent light, said method comprising:
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1) splitting, by using a single beamsplitter having first and second reflecting surfaces, each coated with a reflecting layer, the source beam into a reference beam having a path different than the source beam and a sample beam having a path different than the source beam and the reference beam; 2) directing the reference beam into a reference cell having a substance therein, said substance in the reference cell interacting with the reference beam, said interacting yielding an output reference beam having a direction; 3) directing the sample beam into a sample cell having a substance therein, said substance in the sample cell interacting with the sample beam, said interacting yielding an output sample beam having a direction; 4) detecting at least a portion of the output reference beam and at least a portion of the output sample beam; 5) generating a reference signal representative of the detected portion of the output reference beam and a sample signal representative of the detected portion of the output sample beam; 6) generating a difference signal proportional to the difference between the reference signal and the sample signal; 7) placing the reference substance in the reference cell and in the sample cell; 8) determining a reference spectrum of the reference substance based on the difference signal; 9) moving the beamsplitter in a direction perpendicular to the propagation of the source beam to determine a minimized noise location of the beamsplitter at which a center burst of an interferogram is minimized; 10) determining a baseline difference spectrum; 11) placing the beamsplitter at the determined minimized noise location by moving the beamsplitter and its first and second reflecting surfaces together in a direction perpendicular to the propagation path of the source beam between the first and second linear paths; 12) thereafter placing the reference substance in the reference cell and placing the sample substance in the sample cell; 13) determining a sample difference spectrum; and 14) determining the absorption spectrum of the sample based on the reference spectrum, the baseline difference spectrum and the sample difference spectrum. - View Dependent Claims (15, 16)
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17. A spectrophotometry system comprising:
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a light source generating a light beam; a lens in a path of the light beam and transmitting the light beam as a coherent source light beam; an optical system within the housing including a single moveable beamsplitter having first and second reflecting surfaces, each coated with a reflecting layer, said beamsplitter for splitting the source light beam into; (1) a reference beam reflected by the first reflecting surface to form a first linear path different from the source path, and (2) a sample beam reflected by the second reflecting surface to form a second linear path different from the source path and different from the first linear path, wherein the beamsplitter and its first and second reflecting surfaces are moveable together in a direction perpendicular to the propagation path of the source beam between the first and second linear paths; a reference cell including a reference for interacting with the reference beam wherein said interacting yields an output reference beam having a direction; a reference light detector for detecting at least a portion of the output reference beam based on the direction of the output reference beam and generating a reference signal representative of the detected light; a sample cell including a sample for interacting with the sample beam wherein said interacting yields an output sample beam having a direction; a sample light detector for detecting at least a portion of the output sample beam based on the direction of the output sample beam and generating a sample signal representative of the detected light; a detector circuit for producing a difference signal proportional to the difference between the reference signal and the sample signal; a sealed housing for enclosing the light source, the lens, the optical system including the moveable beamsplitter, the reference cell including the reference, the reference light detector, the sample cell including the sample, the sample light detector, and the detector circuit; and a processor configured to determine a spectrum of the sample based on the difference signal configured to determine and minimize a centerburst of a waveform of an interferogram of the reference beam and the sample beam. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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Specification