METHOD AND APPARATUS FOR SENSING FLUORESCENT SUBSTANCES

• US 3,598,994 A
• Filed: 09/19/1968
• Issued: 08/10/1971
• Est. Priority Date: 09/19/1968
• Status: Expired due to Term

• Current Assignee: David A. Markle
• Original Assignee: David A. Markle
• Inventors: Markle, David A.
• Application Number:
  US04/760,834
• Time in Patent Office: 1,055 Days
• US Class Current: 250/458.1
• CPC Class Codes: G01N 2021/6426 Determining Fraunhofer lines
• CPC Class Codes: G01N 21/645 Specially adapted constructive features of fluorimeters
• CPC Class Codes: G01N 2201/0616 Ambient light is used

Abstract

A method and apparatus for sensing fluorescent radiation emitted by a sample material using sunlight as the source of exciting radiation. A bundle of direct sunlight is encoded and split into beams each of which is combined with similar portions of a bundle of light containing solar reflected and solar-excited fluorescent energy components from the sample material. The sample bundle is encoded differently from the direct sunlight or reference bundle so that it may be distinguished subsequently. The two beams (each of which contain reference and sample components) are passed through two spectral filters and detected photoelectrically. One of the spectral filters is centered on a Fraunhofer absorption line. The other filter is centered a few Angstroms away in the solar continuum. The four signals corresponding to the intensity of the sample and reference beam components passing through each of the two spectral filters are separated electronically and combined in an analogue computer to yield a signal proportional to the fluorescivity of the sample material.

Claims

2. The apparatus according to claim 1 and wherein said means for encoding said bundle of direct sunlight comprises a first light chopper which chops the light at a first frequency and the means for encoding said bundle of reflected sunlight and solar stimulated fluorescent radiation comprises a second light chopper which chops the light at a second frequency different from the first frequency.

3. The apparatus according to claim 2 at wherein said first light chopper chops the light at 240 Hz and the second light chopper chops the light at 480 Hz.

4. The invention according to claim 1 and wherein each filter means comprises a narrowband Fabry-Perot type filter.

5. The invention according to claim 1 and wherein said preselected Fraunhofer absorption line is at 5,890A, wherein said apparatus may be used in sensing the substance rhodamine B.

6. The invention according to claim 1 and wherein said means for measuring the intensity of light passed by each filter means comprises a photomultiplier tube.

7. The invention according to claim 1 and wherein said means for combining the two encoded bundles of light into two different bundles comprise a first beamsplitter assembly for combining the two encoded bundles into a single bundle.

8. A method of sensing the fluorescent radiation emitted by a material when excited by sunlight comprising:

a. forming a bundle of light directly from the sun;

b. forming a bundle of light from the sun reflected by the material;

c. encoding each bundle of light so formed differently;

d. combining both encoded bundles of light into two mixed bundles of light;

e. measuring the intensity of the direct sunlight portion and of the portion that consists of reflected sunlight and solar stimulated fluorescence radiation in each mixed bundle, measuring the intensities thereof both in a wavelength band located within a preselected Fraunhofer absorption line and in a wavelength band that is located near said Fraunhofer absorption line and in the solar continuum, and f. combining said four measurements to determine the proportional solar stimulated fluorescence radiation from the material.

9. Apparatus for use in sensing fluorescent radiation emitted by a target material when illuminated with sunlight comprising:

a. means for collecting radiation directly from the sun and forming thereby a bundle of direct sunlight;

b. means for encoding the bundle of direct sunlight;

c. means for collecting radiation from the target and forming thereby a bundle of reflected sunlight and solar stimulated fluorescence radiation;

d. means for encoding the bundle of target radiation differently from the bundle of direct sunlight;

e. means for combining the two encoded bundles of light into two bundles of mixed light;

f. means for producing a first signal proportional to the intensity of light in one of said bundles over a wavelength band within a preselected Fraunhofer absorption line;

g. means producing a second signal proportional to the intensity of light in the other of said bundles over a wavelength band close to the preselected Fraunhofer absorption lines but in the solar continuum; and

h. means converting each of said first and said second signals into two signals proportional respectively to the intensity of the direct sunlight and to the intensity of the reflected sunlight and solar stimulated fluorescence radiation in the respective bundles thereby producing four signals from which to determine the presence of and relative quantity of solar stimulated fluorescence radiation from the target.

10. The apparatus according to claim 9 includiNg means receiving said four signals and converting them into a single signal proportional to the solar stimulated fluorescence radiation from the target in accordance with the formula:

P 1/A-B (C- DB/A) where;

A the intensity of direct sunlight in the solar continuum close to the Fraunhofer line, B the intensity of direct sunlight within the preselected Fraunhofer line, C the intensity of reflected sunlight and solar stimulated fluorescence within the preselected Fraunhofer line, D the intensity of reflected sunlight and solar stimulated fluorescence in the solar continuum close to the Fraunhofer line.