Spectrosorptance measuring system and method

• US 4,012,144 A
• Filed: 08/07/1975
• Issued: 03/15/1977
• Est. Priority Date: 08/07/1975
• Status: Expired due to Term

• Current Assignee: Varian Associates
• Original Assignee: Varian Associates
• Inventors: Hedelman, Sidney
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Hille, Rolf
• Application Number:
  US05/602,841
• Time in Patent Office: 586 Days
• Field of Search: 356/236, 356/73, 356/96, 356/90, 356/95, 250/228
• US Class Current: 356/73
• CPC Class Codes: G01N 21/255 Details, e.g. use of specially adapted sources, lighting or optical systems

Abstract

Apparatus and method for measuring the absolute absorptance of a relatively thin sample displaying both reflecting and transmitting characteristics. An integrating sphere is provided, and monochromatic reference and sample beams are projected into the sphere from a pair of angularly-spaced ports. Detector means are positioned at the sphere to receive illumination from the internal sphere wall, including the illumination arising from the first reflectance from that portion of the sphere directly illuminated by the sample and reference beams. The reference and sample electrical signals proceeding from the detector are equalized over the wavelength range of the instrument to establish a relatively flat baseline with the sample withdrawn from the sample beam. The sample is then repositioned within the sample beam. By virtue of the position of the detector and the thinness of the sample, the detector views the illumination of the sphere wall, but substantially excludes the first reflectance and scattered energy from the sample. The light falling on the detector due to illumination of the sphere via the sample is compared with the light falling on the detector due to illumination of the sphere by the reference beam, the ratio between the two providing a direct measure of the quantity of incident sample beam energy transmitted and reflected by said sample. By subtracting the thus determined reflectance and transmittance of the sample from unity, the absorptance of the sample may be directly indicated.

Claims

1. Apparatus for measuring the absolute absorptance of a relatively thin sample displaying both specularly reflecting and transmitting characteristics, comprising:

an integrating sphere;

means for directing relatively monochromatic reference and sample beams into said sphere from a pair of angularly spaced ports;

detector means positioned at said sphere to receive illumination from said internal sphere wall, including the illumination arising from the first reflectance from that portion of the sphere wall directly illuminated by said sample and reference beams;

baseline compensator means for equalizing the reference and sample electrical signals from said detector with said sample removed from said sample beam;

means for positioning said sample within said sphere in the path of said sample beam, and at such position with respect to said detector that said detector views the illumination of the sphere wall, and substantially excludes the specular and scattered components of the reflected and transmitted light energy from said sample until after said energy strikes the sphere wall;

ratio electronics means for comparing the light falling on said detector due to illumination of the sphere wall via the sample to the light falling on said detector due to illumination by said reference beam, thereby to directly measure the quantity of incident sample beam energy transmitted and reflected by said sample; and

means for converting the determined ratio into absorptance of the said sample.

2. Apparatus in accordance with claim 1, including monochromator means for generating said reference and sample beams, and means for varying the wavelength of said monochromator output to provide a series of relatively discrete wavelengths for said reference and sample beams.

3. Apparatus in accordance with claim 1, wherein said reference and sample beams are incident from ports displaced approximately equal angular distances from a diameter of said sphere, whereby said beams are incident on a common point of said internal sphere wall.

4. Apparatus in accordance with claim 1, including sample holder means for holding said sample, a bearing block closing a port at one side of said sphere, a shaft extending from said sample holder through said bearing block, and actuator means for displacing said shaft in an inward and outward direction with respect to said sphere, whereby to enable movement of said samples into and out of said sample beam.

5. Apparatus in accordance with claim 1, including a removeable sphere cap mounted at a port of said sphere, at the said common point of incidence of said sample and reference beams, said sphere cap being provided with a diffusely reflecting coating at its side facing internal of said sphere.

6. Apparatus in accordance with claim 5, further including a second sphere cap provided with a diffusely reflecting coating at its internally facing side, said second cap being positioned to intercept the specular reflection from said sample, upon said sample being interposed in said sample beam.

7. A method for measuring the absolute absorptance of a relatively thin sample displaying both reflecting and transmitting characteristics, comprising:

directing relatively monochromatic reference and sample beams into an integrating sphere from a pair of angularly spaced ports;

positioning detector means at said sphere to receive illumination from said internal sphere wall, including the illumination arising from the first reflectance from that portion of the sphere wall directly illuminated by said sample beam;

equalizing the reference and sample electrical signals from said detector means with said sample removed from said sample beam;

positioning said sample within said sphere in the path of said sample beam, and at such location with respect to said detector means that said means views the illumination of the sphere wall, and substantially excludes the specular and scattered components of the reflected and transmitted light energy from said sample until after said energy stikes the sphere wall;

forming a ratio between the light intensity falling on said detector due to illumination of the sphere wall via the sample, and the light intensity falling on said detector due to illumination by said reference beam, thereby to directly measure the quantity of incident sample energy transmitted and reflected by said sample; and

converting the determined ratio into the absorptance of the said sample by deducting said ratio from unity.

8. A method in accordance with claim 7, including varying the wavelengths of said reference and sample beams monochromator output to provide a series of relatively discrete wavelengths for said beams.

9. A method in accordance with claim 7, wherein said reference and sample beams are rendered incident from ports displaced approximately equal angular distances from a diameter of said sphere, whereby said beams are incident on a common point of said internal sphere wall.