United States Patent  [li] Patent Number: 4,749,276
Bragg et al.  Date of Patent: Jun. 7,1988
 LONG PATH ABSORPTION CELL
 Inventors: Susan L. Bragg, Richmond Hts.;
Charles E. Wiswall, Hazelwood, both of Mo.
 Assignee: McDonnell Douglas Corporation, St.
 Appl. No.: 821,795
 Filed: Jan. 23,1986
 Int. CI* G01N 21/09
 UJS. CI 356/245; 250/343;
 Field of Search 356/246, 440; 250/343;
350/588; 219/219; 372/107
 References Cited
U.S. PATENT DOCUMENTS
1,791,254 2/1931 Brockdorff 350/588 X
3,906,226 9/1975 Okabe et al 250/373 X
3,944,834 3/1976 Chuan et al 356/243 X
FOREIGN PATENT DOCUMENTS
3014248 10/1981 Fed. Rep. of Germany 356/246
White, J. U., "Long Optical Paths of Large Aperture", J. Opt. Soc. Am., No. 32 (1942), pp. 285-288. Eng, R. S. et al., "Tunable Diode Laser Measurement of Water Vapor Line Parameters in the 10 to 15 urn Spectral Region", J. of Mol. Spectry., No. 74 (1979), pp. 388-399.
A small volume long path absorption cell of the Whitetype may be used with condensable samples. The absorption cell is temperature controlled and may be operated over a temperature range of —10 degrees C. to 80 degrees C. To prevent condensation of the sample on the mirror surfaces the mirrors are individually temperature controlled and maintained a few degrees above the ambient temperature of the absorption cell. The mirrors are mounted on an Invar framework which is cantilevered from one end of the cell so that variation of the path length due to thermal expansion is minimized. The cell temperature is controlled by a jacket having a heating or cooling fluid. The controls of the mirrors for the cell are adjustable from the exterior of the cell and the entrance paths for the mechanism are sealed so that the cell can be operated at both above and below atmospheric pressure.
19 Claims, 4 Drawing Sheets