Bio-particle fluorescence detector

Radiant energy – Luminophor irradiation – With ultraviolet source

Reexamination Certificate

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Reexamination Certificate

active

06194731

ABSTRACT:

STATEMENT OF GOVERNMENT INTEREST
This invention herein may be manufactured or used by or for the Government for governmental purposes without the payment of any royalties thereon.
BACKGROUND OF THE INVENTION
The present invention relates to the field of the detection of biological aerosols.
Laser based systems are known for the detection of airborne particles of destructive biological particles such as harmful bacteria, individual or groups of cells, or protein particles. In a prior art method, a laser light illuminates air drawn through a duct which may bear the particles to be detected, such light having a wavelength near or at the peak of an absorption resonance in trace gases or chemical elements to be detected. A photodetector responds to the resulting radiation of fluorescent light due to the laser induced biochemical fluorescence. See for example,
FIG. 1
, col. 4-5, of U.S. Pat. No. 4,651,010 to Javan. As mentioned in this patent, it is also known to pulse the illuminating laser beam and gate the receiver coupled to the photodetector to cause it to respond in a delayed manner during a short period following each laser illumination pulse. The delay is fashioned to take advantage of the fluorescence decay time of the agent to be detected, so as to discriminate against false ambient illumination.
It is desired to improve the prior art method mentioned in the Javan patent, of laser illuminating air carrying the particles to be detected, which has been drawn through a duct, to detect the aforesaid fluorescence produced by the illuminating laser beam.
BRIEF SUMMARY OF A PREFERRED EMBODIMENT OF THE INVENTION
The effective sample volume of air passing through the aforesaid duct is greatly increased by multiply passing a pulsed illuminating laser beam several times through several different portions of the volume of air passing through the duct, this operation being facilitated by opposed mirrors positioned within the duct. Thus, the mirrors cause the pulsed beam to follow several multiple paths through the duct to increase the number of particles hit by the beam, and detected by a pair of photodetectors positioned alongside the duct. As a result, a large volume of air is sampled for a duct of relatively small size, and the magnitude of the detected fluorescent light signals is accordingly increased.


REFERENCES:
patent: 5471294 (1995-11-01), Ogino
patent: 5895922 (1999-04-01), Ho

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