External/internal optical adapter with reverse biased photodiodes for FTIR spectrophotometry
First Claim
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1. An adapter for use with a 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;
an optical system within the housing for reflecting the source beam and for splitting the source light beam into a reference beam of reflected light directed in a first path and a sample beam of reflected light directed in a second path different from the first path;
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 biased photodetector 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 biased photodetector 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 wherein the reference light biased photodetector is reverse biased as compared to the sample light photodetector, said reference light biased photodetector generating a reverse biased reference signal or wherein the sample light biased photodetector is reverse biased compared to the reference light photodetector, said sample light biased photodetector generating a reverse biased sample signal;
a detector circuit adapted to produce a difference signal proportional to the difference between the reverse biased reference signal and the sample signal when the reference light biased photodetector is reverse biased or wherein the detector circuit is adapted to produce a difference signal proportional to the difference between the reference signal and the reverse biased sample signal when the sample light biased photodetector is reverse biased; 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
18 Claims
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1. An adapter for use with a spectrophotometry system having a light source generating a source light beam of coherent light, said adapter comprising:
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a sealed housing for receiving the source light beam; an optical system within the housing for reflecting the source beam and for splitting the source light beam into a reference beam of reflected light directed in a first path and a sample beam of reflected light directed in a second path different from the first path; 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 biased photodetector 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 biased photodetector 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 wherein the reference light biased photodetector is reverse biased as compared to the sample light photodetector, said reference light biased photodetector generating a reverse biased reference signal or wherein the sample light biased photodetector is reverse biased compared to the reference light photodetector, said sample light biased photodetector generating a reverse biased sample signal; a detector circuit adapted to produce a difference signal proportional to the difference between the reverse biased reference signal and the sample signal when the reference light biased photodetector is reverse biased or wherein the detector circuit is adapted to produce a difference signal proportional to the difference between the reference signal and the reverse biased sample signal when the sample light biased photodetector is reverse biased; and a processor configured to determine a spectrum of the sample based on the difference signal. - View Dependent Claims (4, 5, 6, 7, 8, 9)
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2. An adapter for use with a spectrophotometry system having a light source generating a source light beam of coherent light, said adapter comprising:
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a sealed housing for receiving the source light beam; an optical system within the housing for splitting the source light beam into a reference beam directed in a first path and a sample beam directed in a second path different from the first path; 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 biased photodetector 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 biased photodetector 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 wherein the reference light biased photodetector comprises a reference photodiode and the sample light biased photodetector comprises a sample photodiode and further comprising a switch selectively electrically connecting a grounded cathode of the reference photodiode and an anode of the sample photodiode and wherein an anode of the reference photodiode is connected to a cathode of the sample photodiode at a point which provides a current signal, and an amplifier converting the current signal into a reference voltage and a difference voltage. - View Dependent Claims (3)
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10. 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 for reflecting the source beam and for splitting the source light beam into a reference beam of reflected light directed in a first path and a sample beam of reflected light directed in a second path different from the first path; 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 biased photodetector 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 biased photodetector 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 wherein the reference light biased photodetector is reverse biased as compared to the sample light photodetector, said reference light biased photodetector generating a reverse biased reference signal or wherein the sample light biased photodetector is reverse biased compared to the reference light photodetector, said sample light biased photodetector generating a reverse biased sample signal; a detector circuit adapted to produce a difference signal proportional to the difference between the reverse biased reference signal and the sample signal when the reference light biased photodetector is reverse biased or wherein the detector circuit is adapted to produce a difference signal proportional to the difference between the reference signal and the reverse biased sample signal when the sample light biased photodetector is reverse biased; a sealed housing for enclosing the above; and a processor configured to determine a spectrum of the sample based on the difference signal. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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11. 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 for splitting the source light beam into a reference beam directed in a first path and a sample beam directed in a second path different from the first path; 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 biased photodetector 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 biased photodetector 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 above; and a processor configured to determine a spectrum of the sample based on the difference signal wherein the reference light biased photodetector comprises a reference photodiode and the sample light biased photodetector comprises a sample photodiode and further comprising a switch selectively electrically connecting a grounded cathode of the reference photodiode and an anode of the sample photodiode and wherein an anode of the reference photodiode is connected to a cathode of the sample photodiode at a point which provides a current signal, and an amplifier converting the current signal into a reference voltage and a difference voltage. - View Dependent Claims (12)
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Specification