SPECTRUM ANALYZING SYSTEM WITH PHOTODIODE ARRAY
 Inventors: Einar S. Mathisen, Poughkeepsie;
Paul A. Schumann, Jr., Wappinger Falls; Alvin H. Tong, Poughkeepsie, aUofN.Y.
 Assignee: International Business Machines Corporation, Armonk, N.Y.
 Appl. No.: 754,810
 Filed: Dec. 27,1976
 Int. CI.* G01J 3/06; G01J 3/42
 U.S. CI 356/308; 356/323;
 Field of Search 356/308, 309, 319, 323,
356/324, 325, 326, 329, 83, 93, 95
 References Cited
U.S. PATENT DOCUMENTS
3,640,627 2/1972 Beattie et al 356/104
3,874,799 4/1975 Isaacs et al 356/97
3,973,849 8/1976 Jackson et al 356/97
Primary Examiner—-Vincent P. McGraw
Attorney, Agent, or Firm—Douglas R. McKechnie
A spectrum analyzing system measures or analyzes the
colorimetric properties of a test sample at a preselected wavelength or range of wavelengths within the ultraviolet, visible, and near infrared regions. The system includes a spectrophotometer provided with a wideband light source, optical devices providing a sample light path and a reference light path, a chopper wheel allowing light to be directed alternately along the sample and reference paths interspersed with dark periods during which no light travels along either path, a dispersion grating for dispersing the light from both paths, a series of neutral density filters for limiting to various degrees the amount of light traversing each path, and a linear array of photodiodes for detecting the dispersed light at different wavelengths. The system also includes an electronic control section including a programmable power supply for controlling the intensity of light from the light source whereby the combination of the use of the neutral density filters in conjunction with controlling the intensity of light from the light source can be used to operate the photodiode array to prevent operation thereof near the saturated and dark current levels, and means for scanning the photodiode array at high speeds during rotation of the chopper wheel to provide a high speed spectral readout.