Intra-cavity total reflection for high sensitivity measurement of optical properties
First Claim
1. An intra-cavity total reflection apparatus for high sensitivity measurement of the optical absorption of a test material, said apparatus comprising:
- injecting means for producing light for a predetermined length of time;
an optical cavity, comprising first, second and third reflecting surfaces integrally formed on a cavity medium, for receiving said light produced by said injecting means and for providing total internal reflection of said light within said cavity so as to generate an evanescent wave at said third reflecting surface which decays within a decay length outside of said cavity beyond said third reflecting surface, the test material being disposed outside of said cavity within said decay length, and said injected light oscillating between said first and second reflecting surfaces such that a portion of said injected light escapes from said cavity; and
measuring means disposed adjacent one of said first and said second reflecting surfaces for monitoring said portion of said injected light that escapes from said cavity to determine the amount of decay time said light takes to decay within said cavity and the optical absorption of said test material.
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Abstract
An optical cavity resonator device is provided for conducting sensitive murement of optical absorption by matter in any state with diffraction-limited spatial resolution through utilization of total internal reflection within a high-Q (high quality, low loss) optical cavity. Intracavity total reflection generates an evanescent wave that decays exponentially in space at a point external to the cavity, thereby providing a localized region where absorbing materials can be sensitively probed through alteration of the Q-factor of the otherwise isolated cavity. When a laser pulse is injected into the cavity and passes through the evanescent state, an amplitude loss resulting from absorption is incurred that reduces the lifetime of the pulse in the cavity. By monitoring the decay of the injected pulse, the absorption coefficient of manner within the evanescent wave region is accurately obtained from the decay time measurement.
39 Citations
9 Claims
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1. An intra-cavity total reflection apparatus for high sensitivity measurement of the optical absorption of a test material, said apparatus comprising:
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injecting means for producing light for a predetermined length of time; an optical cavity, comprising first, second and third reflecting surfaces integrally formed on a cavity medium, for receiving said light produced by said injecting means and for providing total internal reflection of said light within said cavity so as to generate an evanescent wave at said third reflecting surface which decays within a decay length outside of said cavity beyond said third reflecting surface, the test material being disposed outside of said cavity within said decay length, and said injected light oscillating between said first and second reflecting surfaces such that a portion of said injected light escapes from said cavity; and measuring means disposed adjacent one of said first and said second reflecting surfaces for monitoring said portion of said injected light that escapes from said cavity to determine the amount of decay time said light takes to decay within said cavity and the optical absorption of said test material. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification
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- Resources
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Current AssigneeThe United States of America As Represented By The Secretary of Agriculture
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Original AssigneeTHE GOVERNMENT OF THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF COMMERCE
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InventorsPipino, Andrew Charles Rule
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Primary Examiner(s)Kim, Robert H.
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Application NumberUS09/188,415Time in Patent Office371 DaysField of Search356/439, 356/440, 356/246, 356/445, 356/432, 356/136, 356/244US Class Current356/440CPC Class CodesG01J 3/42 Absorption spectrometry; Do...G01N 21/031 Multipass arrangementsG01N 21/552 Attenuated total reflectionG01N 30/74 Optical detectors measureme...
