Optics: measuring and testing – For light transmission or absorption – Of fluent material
Patent
1997-10-31
1998-11-10
McGraw, Vincent P.
Optics: measuring and testing
For light transmission or absorption
Of fluent material
356436, 356437, G01N 2131
Patent
active
058352317
ABSTRACT:
A broadband, ultrahigh-sensitivity chemical sensor is provided that allows etection through utilization of a small, extremely low-loss, monolithic optical cavity. The cavity is fabricated from highly transparent optical material in the shape of a regular polygon with one or more convex facets to form a stable resonator for ray trajectories sustained by total internal reflection. Optical radiation enters and exits the monolithic cavity by photon tunneling in which two totally reflecting surfaces are brought into close proximity. In the presence of absorbing material, the loss per pass is increased since the evanescent waves that exist exterior to the cavity at points where the circulating pulse is totally reflected, are absorbed. The decay rate of an injected pulse is determined by coupling out an infinitesimal fraction of the pulse to produce an intensity-versus-time decay curve. Since the change in the decay rate resulting from absorption is inversely proportional to the magnitude of absorption, a quantitative sensor of concentration or absorption cross-section with 1 part-per-million/pass or better sensitivity is obtained. The broadband nature of total internal reflection permits a single device to be used over a broad wavelength range. The absorption spectrum of the surrounding medium can thereby be obtained as a measurement of inverse decay time as a function of wavelength.
REFERENCES:
patent: 4571085 (1986-02-01), Anderson
patent: 4793709 (1988-12-01), Jabar et al.
patent: 5437840 (1995-08-01), King et al.
McGraw Vincent P.
The United States of America as represented by the Secretary of
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