Method for enhanced evanescent field exposure in an optical fiber resonator for spectroscopic detection and measurement of trace species

• US 20060177939A1
• Filed: 03/27/2006
• Published: 08/10/2006
• Est. Priority Date: 12/12/2001
• Status: Active Grant

• Current Assignee: Kevin K. Lehmann, Paul Rabinowitz, Peter B. Tarsa
• Original Assignee: Kevin K. Lehmann, Paul Rabinowitz, Peter B. Tarsa
• Inventors: Tarsa, Peter B., Rabinowitz, Paul, Lehmann, Kevin K.
• Granted Patent: US 7,504,263 B2
• Time in Patent Office: Days
• US Class Current: 436/164
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 2021/391 Intracavity sample
• CPC Class Codes: G01N 2021/7789 Cavity or resonator
• CPC Class Codes: G01N 21/39 using tunable lasers
• CPC Class Codes: G01N 21/552 Attenuated total reflection

Abstract

A method for detection and measurement of trace species in a gas or liquid sample is provided. The method comprises forming a sensor from an optical fiber by tapering a portion the optical fiber along a length thereof, exposing the tapered portion of the optic fiber to the sample gas or sample liquid, emitting radiation from a coherent source, coupling at least a portion of the radiation emitted from the coherent source into the fiber optic ring, receiving a portion of the radiation traveling in the fiber optic ring, and determining the level of trace species in the gas or liquid sample based on a rate of decay of the radiation within the fiber optic ring.

Claims

1. A method for detecting and measuring a trace species in at least one of a sample gas and a sample liquid, the method comprising:

forming a sensor from an optical fiber by tapering a portion the optical fiber along a length thereof;

exposing the tapered portion of the optic fiber to the sample gas or sample liquid;

emitting radiation from a coherent source;

coupling at least a portion of the radiation emitted from the coherent source into the fiber optic ring;

receiving a portion of the radiation traveling in the fiber optic ring; and

determining the level of trace species in the gas or liquid sample based on a rate of decay of the radiation within the fiber optic ring.

2. A method according to claim 1, further comprising:

forming with a predetermined radius at least a portion of the tapered portion of the passive fiber optic ring based on an absorption frequency of the trace species; and

exposing the formed portion of the sensor to the sample liquid or sample gas.

3. A method according to claim 2, further comprising exposing an evanescent field of the radiation traveling within the fiber to the sample gas or sample liquid.

4. A method according to claim 3, further comprising determining the level of the trace species in the sample gas or sample liquid based on the rate of decay of the radiation in the fiber responsive to an absorption of the radiation by the trace species.

5. A method for detecting and measuring a trace species in at least one of a sample gas and a sample liquid, the method comprising:

forming a sensor from an optical fiber by removing a portion of a cladding of the optical fiber to form a “

D”

shaped cross section;

exposing the “

D”

shaped cross section portion of the optic fiber to the sample gas or sample liquid;

emitting radiation from a coherent source;

coupling at least a portion of the radiation emitted from the coherent source into the fiber optic ring;

receiving a portion of the radiation traveling in the fiber optic ring; and

determining the level of trace species in the gas or liquid sample based on a rate of decay of the radiation within the fiber optic ring.

6. A method according to claim 5, further comprising:

forming with a predetermined radius at least a portion of the “

D”

shaped cross section portion of the passive fiber optic ring based on an absorption frequency of the trace species; and

exposing the formed portion of the sensor to the sample liquid or sample gas.

7. A method according to claim 6, further comprising exposing an evanescent field of the radiation traveling within the fiber to the sample gas or sample liquid.

8. A method according to claim 7, further comprising determining the level of the trace species in the sample gas or sample liquid based on the rate of decay of the radiation in the fiber responsive to an absorption of the radiation by the trace species.