Optogalvanic spectroscopy with phase independent detection
AssigneeAlimenterics Inc.
InventorsMichael J. Colgan, Hans P. Lie
Life of this patent
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Abstract
In an optogalvanic spectroscopy system, a plasma is exposed to light at a wavelength associated with a particular species in the analyte. The light is amplitude modulated. The amplitude of a modulated component in the signal representing electrical impedance of the plasma is detected in a phase independent manner, so that the detected amplitude is substantially independent of the phase of the modulated component in the impedance signal relative to the amplitude modulation of the light. The system has reduced sensitivity to changes in the spectrum of the applied light.
Claims17
A method of determining the composition of an analyte including the steps of:
- (a) maintaining the analyte in gaseous form in an electrical discharge;
- (b) applying first radiation to said analyte in said discharge so that said radiation interacts with a first species in said analyte to produce an optogalvanic effect;
- (c) monitoring electrical impedance of said discharge and providing an impedance signal representing said impedance;
- (d) periodically varying the amplitude of said first radiation at a first modulation frequency, whereby said impedance signal will include a first component varying at a first component frequency equal to the first modulation frequency or a harmonic thereof;
- and
- (e) detecting the amplitude of said first component to provide a first value representing said amplitude of said first component, whereby said first value represents the amount of said first species in said analyte, said detecting step being performed so that said value is substantially independent of the phase of said first component relative to the phase of said periodic variation in amplitude of said first radiation.
Optogalvanic spectroscopy apparatus comprising:
- (a) means for maintaining the analyte in gaseous form in an electrical discharge;
- (b) means for applying first radiation to said analyte in said discharge so that said radiation interacts with a first species in said analyte to produce an optogalvanic effect;
- (c) means for monitoring electrical impedance of said discharge and providing an impedance signal representing said impedance;
- (d) means for periodically varying the amplitude of said first radiation at a first modulation frequency, whereby said impedance signal will include a first component varying at a first component frequency equal to the first modulation frequency or a harmonic thereof;
- and
- (e) means for detecting the amplitude of said first component to provide a first value representing said amplitude of said first component, whereby said first value represents the amount of said first species in said analyte, said detecting means being operative to detect said amplitude so that said value is substantially independent of the phase of said first component relative to the phase of said periodic variation in amplitude of said first radiation.
Dependencies are inferred from the claim text.