Reflectometer employing an integrating sphere and lens-mirror concentrator

• US 5,517,315 A
• Filed: 10/29/1993
• Issued: 05/14/1996
• Est. Priority Date: 10/29/1993
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Chenault, David B., Schiff, Roy, Snail, Keith A., Hanssen, Leonard M.
• Primary Examiner(s): Evans, F. L.
• Assistant Examiner(s): KIM, ROBERT H
• Application Number:
  US08/143,098
• Time in Patent Office: 928 Days
• Field of Search: 356/346, 356/445, 356/448, 356/236
• US Class Current: 356/445
• CPC Class Codes: G01N 21/474 Details of optical heads therefor, e.g. using optical fibres

Abstract

A reflectometer wherein a light having a predetermined wavelength is projected into an integrating sphere containing a sample whose reflectance is to be measured. As the projected light strikes the sample, rays are reflected back the walls of the integrating sphere; some of which strike the area within the field-of-view of a concentrator. The rays striking within the field-of-view of the concentrator are focused upon a detector element which allows one to determine the reflectance of the sample. A control means is utilized to control the wavelength of the projected light through a spectrophotometer, and calculate the reflectance of the sample.

Claims

1. A reflectometer for measuring the reflectance of a sample comprising:

a light source for generating a light beam having a plurality of wavelengths;

means for selecting a predetermined wavelength to be projected onto the sample from the plurality of wavelengths generated by the light source;

an integrating sphere;

means for projecting the predetermined wavelength of light onto a sample located within the integrating sphere where it is reflected in a plurality of directions off the sample onto the wall of the integrating sphere where the reflected light is again reflected;

the integrating sphere being further comprised of a detector for measuring the quantum of light reflected off the sample, a non-imaging concentrator having a hyperbolic mirror directing the reflected light from the sample onto the detector and one or more baffles to shield the concentrator from first reflections of the light off of the sample thereby forming a viewable field which is less than the maximum field-of-view of the concentrator;

means for determining the reflectance of the sample based upon a quantum of light reflected off the sample; and

means for displaying the reflectance of the sample.

2. A reflectometer, as in claim 1, further comprising a means for controlling the selection of the wavelength to be projected onto the sample, recording, analyzing the reflectance of the sample for presentation on the display means.

3. A reflectometer, as in claim 2, wherein the control means is a computer.

4. A reflectometer, as in claim 1, wherein the light beam is an ultraviolet (UV) light beam.

5. A reflectometer, as in claim 1, wherein the light beam is an infrared (I) light beam.

6. A reflectometer, as in claim 1, wherein the light beam is selected from a group consisting of, an ultraviolet (UV) light and an infrared (IR) light.

7. A reflectometer, as in claim 1, further comprised of a gas medium surrounding the light beam, and a means for drying the gas medium surrounding the light beam.

8. A reflectometer, as in claim 1, wherein the non-imaging concentrator is comprised of a compound hyperbolic concentrator and a lens.

9. A reflectometer, as in claim 1, wherein the means for selecting a predetermined wavelength of light to be projected onto the sample and the means for projecting the predetermined wavelength of light onto the sample is a spectrophotometer.

10. A reflectometer, as in claim 9, wherein the spectrophotometer is a dispersive type.

11. A reflectometer, as in claim 1, wherein the means for selecting a predetermined wavelength of light to be projected onto a sample and the means for projecting the predetermined wavelength of light onto the sample is an interferometer.

12. A reflectometer, as in claim 11, wherein the interferometer is a Michelson-type interferometer.

13. A reflectometer, as in claim 1, further comprising a reference sample for calibrating the reflectometer.

14. A reflectometer, as in claim 1, wherein the display means is a video display.

15. A reflectometer for measuring the reflectance of a sample comprising:

a light source capable of generating a beam of light having a plurality of wavelengths;

means for surrounding the beam of light with a non-absorbing gas to prevent absorption of absorptive bands present in the beam of light by ambient air;

means for transmitting a band of predetermined wavelengths generated by the light source;

means for selecting a plurality of predetermined wavelengths to be projected onto the sample from the predetermined band of wavelengths generated by the light source;

an integrating sphere, which is further comprised of a concentrator and a detector for measuring the beam of light reflected off the sample and one or more baffles to shield the concentrator from first reflections of the beam of light off the sample thereby forming a cap radius, F, or viewable field, which is less than the maximum field-of-view of the concentrator, and

means of recording and analyzing the reflected light of the plurality of predetermined wavelengths measured by the concentrator and detector to obtain a total reflectance of the sample and displaying the total reflectance of the sample on a display.

16. A reflectometer, as in claim 15, further comprised of a standard reference material of known reflectivity for calibrating the integrating sphere by comparing a reflectance of the standard reference material to the recorded reflectance obtained by the recording and analyzing means.

17. A method for determining a total reflectance of a sample comprising the steps of:

selecting a wavelength of a light beam to be projected onto a sample located within an integrating sphere whose reflectivity is to be determined;

projecting the light into the integrating sphere through a spectrophotometer onto the sample;

collecting a reflected light from the sample and the walls of the integrating sphere projected onto a cap radius, F, of the integrating sphere with a concentrator having a predetermined field-of-view;

measuring the reflected light collected by the concentrator to ascertain a reflectance of the sample at the preselected wavelength;

repeating the step of selecting the wavelength of the light to be projected into the integrating sphere by varying the preselected wavelength over a predetermined plurality of wavelengths;

analyze the plurality of reflectivity measurements to obtain the total reflectance of the sample for the predetermined plurality of wavelengths;

projecting a light beam through the spectrophotometer onto a standard reference material inside the integrating sphere and obtain a calibration factor for the integrating sphere by comparing the standard reflectance of the standard reference material to the reading of a calibration reflectance;

correct the total reflectivity by applying the correction factor; and

display the corrected total reflectance of the sample on a display.

18. A method, as in claim 17, further comprising the step of drying the gas surrounding the light beam prior to projecting the light beam into the integrating sphere to prevent absorption of the light beam by absorptive bands in the surrounding gas.

19. A method for determining the reflectance of a sample, as in claim 17, wherein the concentrator is comprised of a compound hyperbolic concentrator and a lens.

20. A method for determining the reflectance of a sample, as in claim 17, wherein the concentrator is comprised of a trumpet-type concentrator and a lens.