System for performing spectral analyses under computer control

Claim 5

In a spectrophotometric system having data acquisition means for generating digital value-representing signals in response to sensed optical inputs and also having a digital computer provided with data storage means and data processing means which are responsive to the output of said data acquisition means, a method of operating said system to measure the thickness of a film sample of given dielectric material, comprising the steps of: a. conducting to said film sample, during each of a series of nonadjacent time periods, a beam of variable-wavelength monochromatic light furnished by a given source, the wavelength of said beam varying at a given rate through a specified range of wavelength values during each of said periods; b. conducting to a light-sensitive input device in said data acquisition means the light which is reflected from said sample when it is impinged by said beam; c. conducting directly to said light-sensitive device, without impinging said sample and during time periods intervening those specified in step a, the beam of variable-wavelength monochromatic light furnished by said source, the wavelength of which varies at said given rate through said specified range of values during each of said intervening periods; d. operating said computer to receive and store in said data storage means, at regularly timed intervals in each of the time periods described in a and c, the digital values generated by said data acquisition means, thereby to store at least two sets of numbers, one set representing the respective intensities of light detected by said light-sensitive device at said timed intervals during a period when the variable-wavelength light beam is being conducted directly to said device, and the other set of numbers representing the respective intensities of light detected by said device at said timed intervals during a period when the variable-wavelength light beam is impinging said film sample; e. storing in said data storage means a set of numbers representing the respective wavelengths of the light beam at the respective ones of said timed intervals throughout any of said periods; f. operating said data processing means to derive from all of the stored number sets recited hereinabove a table of values representing the manner in which the relative reflectance of said film sample varies with respect to the wavelength of the incident light beam under a hypothetical condition where it is assumed that the incident light has uniform intensity for all wavelengths in said range and all system components have constant operating characteristics; g. operating said data processing means to multiply the relative reflectance values in said table by a factor which will convert the curve of relative reflectance versus wavelength to a curve which is at least approximately tangent to predefined upper and lower wave envelopes that bound the curves of absolute reflectance versus wavelength for all films of the given material having thicknesses within a predetermined thickness range; and h. operating said data processing means to compute from the multiplied reflectance values the thickness of said film sample.

Claim 6

In a spectrophotometric system having data acquisition means for generating digital value-representing signals in response to sensed optical inputs and also having a digital computer provided with data storage means and data processing means which are responsive to the output of said data acquisition means, a method of operating said system to measure the thickness of a film sample of given dielectric material, comprising the steps of: a. conducting to said film sample, during each of a series of nonadjacent time periods, a beam of variable-wavelength monochromatic light furnished by a given source, the wavelength of said beam varying at a given rate through a specified range of wavelength values during each of said periods; b. conducting to a light-sensitive input device in said data acquisition means the light which is reflected from said sample when it is impinged by said beam; c. conducting directly to said light-sensitive device, without impinging said sample and during time periods intervening those specified in step a, the beam of variable-wavelength monochromatic light furnished by said source, the wavelength of which varies at said given rate through said specified range of values during each of said intervening periods; d. operating said computer to receive and store in said data storage means, at regularly timed intervals in each of the time periods described in a and c, the digital values generated by said data acquisition means, thereby to store at least two sets of numbers, one set representing the respective intensities of light detected by said light-sensitive device at said timed intervals during a period when the variable-wavelength light beam is being conducted directly to said device, and the other set of numbers representing the respective intensities of light detected by said device at said timed intervals during a period when the variable-wavelength light beam is impinging said film sample; e. storing in said data storage means a set of numbers representing the respective wavelengths of the light beam at the respective ones of said timed intervals throughout any of said periods; f. operating said data processing means to derive from all of the stored number sets recited hereinabove a table of values representing the manner in which the relative reflectance of said film sample varies with respect to the wavelength of the incident light beam under a hypothetical condition where it is assumed that the incident light has uniform intensity for all wavelengths in said range and all system components have constant operating characteristics; g. operating said data processing means to multiply the relative reflectance values in said table by a factor which will convert the curve of relative reflectance versus wavelength to a curve which is at least approximately tangent to predefined upper and lower wave envelopes that bound the curves of absolute reflectance versus wavelength for all films of the given material having thicknesses within a predetermined thickness range; and h. operating said data processing means to compute from the multiplied reflectance values the thickness of said film sample.

Claim 7

A computer-controlled spectrophotometric system for measuring a property of a given material sample which is subject to spectral analysis, said system comprising: a. cyclically operable illuminating means for furnishing a beam of monochromatic light, the wavelength of which varies periodically at a given rate through a specified range of wavelength values; b. a light detector; c. first light guiding means for conducting said light beam through a first path directly to said light detector during nonadjacent ones of the periods in which the wavelength of said light beam undergoes variation through said range of values; d. second light guiding means effective during periods intervening said nonadjacent periods for conducting said light beam through a second path having an initial portion that directs said beam to said sample and a final portion that conducts light from said sample to said detector; e. signal converting and data transfer means responsive to the output of said detector and operating in a timed relationship with the cyclic operation of said illuminating means for producing sequences of digital value representations, each such sequence denoting the variation of detected light intensity with respect to the wavelengths of said beam at a series of regularly timed intervals within each of said periods; and f. a digital computer having data storage means for storing the sequences of digital value representations produced by said means e during at least two successive periods when said detector is receiving light through said first path and said second path, respectively, and having data processing means to calculate from such stored data the optical responses which would have been obtained from said sample at said timed intervals if the conditions had been such that the intensity of the variable-wavelength incident light were uniform at all wavelengths in said range and the operating characteristics of the components of said system were constant, thereby providing a new set of corrected values from which the measurement of said sample property can be accurately determined.

Claim 8

A computer-controlled spectrophotometric system for measuring a property of a given material sample which is subject to spectral analysis, said system comprising: a. cyclically operable illuminating means for furnishing a beam of monochromatic light, the wavelength of which varies periodically at a given rate through a specified range of wavelength values; b. a light detector; c. first light guiding means for conducting said light beam through a first path directly to said light detector during nonadjacent ones of the periods in which the wavelength of said light beam undergoes variation through said range of values; d. second light guiding means effective during periods intervening said nonadjacent periods for conducting said light beam through a second path having an initial portion that directs said beam to said sample and a final portion that conducts light from said sample to said detector; e. signal converting and data transfer means responsive to the output of said detector and operating in a timed relationship with the cyclic operation of said illuminating means for producing sequences of digital value representations, each such sequence denoting the variation of detected light intensity with respect to the wavelengths of said beam at a series of regularly timed intervals within each of said periods; and f. a digital computer having data storage means for storing the sequences of digital value representations produced by said means e during at least two successive periods when said detector is receiving light through said first path and said second path, respectively, and having data processing means to calculate from such stored data the optical responses which would have been obtained from said sample at said timed intervals if the conditions had been such that the intensity of the variable-wavelength incident light were uniform at all wavelengths in said range and the operating characteristics of the components of said system were constant, thereby providing a new set of corrected values from which the measurement of said sample property can be accurately determined.

Claim 9

A spectrophotometric system as set forth in claim 4 wherein said illuminating means a comprises the following elements: a1. a source of polychromatic light; a2. first light conducting means for directing polychromatic light from said source to an exit point optically aligned with but spaced from the entrance to said first path in said first light guiding means; a3. second light conducting means for directing polychromatic light from said source to an exit point oPtically aligned with but spaced from the entrance to said second path in said second light guiding means; and a4. a rotatable variable-wavelength interference filter positioned so that it rotates alternately past the entrance to said first path and the entrance to said second path, the wavelength of the monochromatic light transmitted by said filter to either path depending upon the angular position of said filter.

Claim 10

A spectrophotometric system as set forth in claim 5 wherein each of said light conducting means and light guiding means is a fiber-optic bundle.

Claim 11

A system as set forth in claim 6 wherein said second light guiding means (d) is a bifurcated fiber-optic bundle, one branch of which constitutes said initial portion, and the other branch of which constitutes said final portion.

Claim 12

A spectrophotometric system as set forth in claim 4 which includes timing means under the control of said illuminating means for causing said signal converting and data transfer means to sample the output of said light detector at predetermined wavelength increments during each of the periodic variations of the monochromatic beam wavelength.

Claim 13

A spectrophotometric system as set forth in claim 4 wherein said computer is programmed to divide each of the values in the sequence that was received through said second path by the correspondingly positioned value in the sequence that was received through said first path.

Claim 14

A spectrophotometric system as set forth in claim 4 wherein said second light guiding means is arranged so that light passed through said initial portion thereof is reflected from said sample and passed through said final portion thereof to said detector.

Claim 15

A system as set forth in claim 10 wherein said computer is programmed to divide each of the values in the sequence that was received through said second path by the correspondingly positioned value in the sequence that was received through said first path, thereby to yield said sequence of corrected values representing the relative reflectance of said sample at the respective wavelengths assumed by said beam at said timed intervals.

Claim 16

A system as set forth in claim 11 wherein said computer is programmed to multiply each of the values in said relative reflectance sequence by a factor which will cause the multiplied values to define a curve that is tangent to at least one of a pair of predetermined wave envelope curves which bound all curves of absolute reflectance versus wavelength for the given material, thereby providing a set of absolute reflectance values for said respective wavelengths.

Claim 17

A system as set forth in claim 12 wherein said computer is programmed to calculate from said sequence of absolute reflectance values the thickness of said sample.

Claim 18

In a computer-controlled spectrophotometric system of the kind wherein a light detector is arranged to respond to light of periodically varying wavelength which is received alternately through a sample measurement path and a direct reference path, the combination comprising: a. a rotatable variable-wavelength filter having a light-transmitting portion with an angular span not exceeding 180* positioned so that it transmits light into the respective entrances of said measurement path and said reference path during different periods in its rotation, the wavelength of the light transmitted into either of said paths at any instant depending upon the angular position of said filter relative to the path entrance; b. a polychromatic light source; and c. means providing light conducting paths leading from said light source to exits on the side of said filter which is farthest from said measurement path and reference path entrances, said path exits being respectively aligned optically with said entrances, whereby the rotation of said filter causes polychromatic light emerging from said path exits to be transmitted by said filter as monochromatic light of varying wavelength to said measurement path and said reference path, respectively, during different periods in the rotation of said filter.

Claim 19

In a computer-controlled spectrophotometric system of the kind wherein a light detector is arranged to respond to light of periodically varying wavelength which is received alternately through a sample measurement path and a direct reference path, the combination comprising: a. a rotatable variable-wavelength filter having a light-transmitting portion with an angular span not exceeding 180* positioned so that it transmits light into the respective entrances of said measurement path and said reference path during different periods in its rotation, the wavelength of the light transmitted into either of said paths at any instant depending upon the angular position of said filter relative to the path entrance; b. a polychromatic light source; and c. means providing light conducting paths leading from said light source to exits on the side of said filter which is farthest from said measurement path and reference path entrances, said path exits being respectively aligned optically with said entrances, whereby the rotation of said filter causes polychromatic light emerging from said path exits to be transmitted by said filter as monochromatic light of varying wavelength to said measurement path and said reference path, respectively, during different periods in the rotation of said filter.

Claim 20

The combination set forth in claim 14 wherein said means c is a split fiber-optic bundle having branches leading respectively to said exits and having a common portion adjacent to said light source wherein the fibers of said branches have a randomized distribution.