Gas spectroscopy
First Claim
1. A spectroscopy device, comprising:
- a laser diode; and
a circuit which generates a laser diode driving current, said laser diode driving current having a periodic waveform comprising a plurality of constant current intervals, a first current magnitude being generated during one of said constant current intervals of a period, a second current magnitude being generated during another of said constant current intervals of said period, a third current magnitude being generated during another of said constant current intervals of said period, said laser diode driving current being supplied to said laser diode.
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Accused Products
Abstract
A spectroscopy device comprises a laser diode/lens assembly driven by a periodic stepped laser diode drive current. Each period of the stepped laser diode drive current has a plurality of constant current intervals: a left baseline interval, a left skirt interval, a peak interval, a right skirt interval, and a right baseline interval. The left and right skirt constant current intervals are used to lock the laser radiation emitted from the laser diode onto a preselected absorption line. The left and right baseline constant current intervals are used to subtract baseline absorption measurements from peak constant current interval absorption measurements. A high frequency common mode noise rejection circuit rejects noise common to a monitor radiation detector and a radiation detector which detects radiation passing through a sample cell. A serial line locking cell is provided to allow locking when little or no absorbing material is present in the sample cell. A heated sample cell is provided to allow for the measurement of oxygen concentration in human breath. The pressure and temperature of the gas in the sample cell are detected to account for pressure and temperature dependencies of the absorption measurement. Techniques are disclosed for minimizing the effects of unwanted reflections off various surfaces of a spectroscopy device which otherwise would reflect back into the laser diode.
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Citations
34 Claims
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1. A spectroscopy device, comprising:
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a laser diode; and a circuit which generates a laser diode driving current, said laser diode driving current having a periodic waveform comprising a plurality of constant current intervals, a first current magnitude being generated during one of said constant current intervals of a period, a second current magnitude being generated during another of said constant current intervals of said period, a third current magnitude being generated during another of said constant current intervals of said period, said laser diode driving current being supplied to said laser diode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. An absorption spectroscopy device, comprising:
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a laser diode; a detector; and means for supplying a periodic laser diode driving current to said laser diode, each period of said periodic laser diode driving current having a first constant current interval, a second constant current interval, and a third constant current interval, a first constant current magnitude being supplied to said laser diode during said first constant current interval, a second constant current magnitude being supplied to said laser diode during said second constant current interval, a third constant current magnitude being supplied to said laser diode during said third constant current interval, said means also being for controlling said first constant current and said second constant current such that a current output by said detector during said first constant current interval substantially equals a current output by said detector during said second constant current interval. - View Dependent Claims (23, 24, 25, 26)
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27. A method, comprising:
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increasing an accumulated voltage on a node during a sequence of a plurality of constant current intervals until said accumulated voltage exceeds a predetermined voltage, an increase in said accumulated voltage during each interval of said plurality of intervals being indicative of an absorbance of laser radiation absorbed in a sample cell during said interval; generating a digital value from said accumulated voltage using an analog-to-digital converter after said accumulated voltage exceeds said predetermined voltage; and zeroing said accumulated voltage after said accumulated voltage exceeds said predetermined voltage. - View Dependent Claims (28, 29, 30)
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31. An absorption spectroscopy device, comprising:
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a sample cell; a line locking cell; a beam splitter; a laser diode which emits laser radiation, a first portion of said laser radiation passing through at least a part of said line locking cell and being reflected off said beam splitter, a second portion of said laser radiation passing through said sample cell without being reflected off said beam splitter; and a circuit comprising a first detector and a second detector, said circuit supplying a laser diode driving current to said laser diode, said laser diode driving current having a periodic waveform, each period having a stepped waveform comprising substantially only constant current intervals and brief current switching episodes, each period having at least three constant current intervals, each of said three constant current intervals having a different current magnitude. - View Dependent Claims (32, 33, 34)
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Specification