Spectrometric optical method and system providing required signal-to-noise of measurements

• US 8,049,882 B2
• Filed: 11/16/2005
• Issued: 11/01/2011
• Est. Priority Date: 11/16/2004
• Status: Active Grant

• Current Assignee: Nova Ltd.
• Original Assignee: Nova Measuring Instruments Limited (Honeywell International Inc.)
• Inventors: Finarov, Moshe
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US11/719,419
• Publication Number:
  US 20090135419A1
• Time in Patent Office: 2,176 Days
• Field of Search: 356/326, 356/328
• US Class Current: 356/326
• CPC Class Codes: G01J 2003/2866 Markers; Calibrating of scan
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0218 using optical fibers
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08

Abstract

A system and method for use in spectrometric measurements of an article using selecting an optimal integration time range of the light detection system during which the measurement is to be applied, the optimal integration time being that at which a required value of signal to noise ratio (SNR) of the measurements is obtainable.

Claims

1. A method for use in spectrometric measurements of an article using an optical system having an illumination system and a light detection system, the method comprising selecting an optimal integration time range of the light detection system during which the measurement is to be applied, said optimal integration time being that at which a required value of signal to noise ratio (SNR) of the measurements is obtainable, wherein the optimal integration time is determined using an a priori known value of a spectral reflectance of the article, and a pre-defined spectral characteristic of the measurement system, said optimal integration time being selected such that the highest value of a measured signal is slightly lower than a signal corresponding to a saturation level of the detection system, while the lowest value of the measured signal corresponds to a value of the SNR slightly above the required SNR value.

2. A method for use in spectrometric measurements of an article using an optical system having an illumination system and a light detection system, the method comprising selecting an optimal integration time range of the light detection system during which the measurement is to be applied, said optimal integration time being that at which a required value of signal to noise ratio (SNR) of the measurements is obtainable, wherein said selecting of the optimal integration time range comprises applying a preliminary spectral measurement with a relatively small integration time value such that at least one intensity value of the preliminary measured signal is higher than that corresponding to a predetermined minimal value of the SNR, thereby allowing to determine the reflectance of the article under measurements and calculate the optimal value for the integration time needed for the actual measurement in said article, said optimal integration time being selected such that the highest value of a measured signal is slightly lower than a signal corresponding to a saturation level of the detection system, while the lowest value of the measured signal corresponds to a value of the SNR slightly above the required SNR value.

3. A method for use in spectrometric measurements of an article using an optical system having an illumination system and a light detection system having a limited dynamic range, the measurement system having highly non-uniform spectral characteristics, the method comprising selecting an optimal integration time range of the light detection system during which the measurement is to be applied, said optimal integration time being that at which a required value of signal to noise ratio (SNR) of the measurements is obtainable, said optimal integration time being selected such that the highest value of a measured signal is slightly lower than a signal corresponding to a saturation level of the detection system, while the lowest value of the measured signal corresponds to a value of the SNR slightly above the required SNR value, wherein said selecting of the optimal integration time range comprises applying first and second sequential preliminary measurements to the article using a certain integration time, one of said first and second measurements being such that the highest value of the measured signal being below the saturation level while a part of the measured signal being under the minimal SNR level;

and the other measurement being such that the lowest value of the corresponding measured signal being above the minimal SNR level while a part of said signal being in saturation.

4. The method of claim 3, wherein said certain integration time is selected so as to provide that the first and second measured signals include at least one common spectral range, in which both of the measured signals are within an allowed range of value of a measured signal defined by the require SNR, which is between the minimal SNR level and the saturation level.

5. The method of claim 4, wherein said certain integration time is selected so as to provide that the first and second measured signals include at least two common spectral ranges.

6. The method of claim 4, utilizing said at least one common spectral range to calculate a ratio between the first and second measured signals in said at least one common spectral range.

7. The method of claim 6, comprising averaging said at least one common spectral range and extrapolating it to other spectral ranges.

8. The method of claim 5, comprising utilizing the calculated ratio to combine the first and second measured spectral signals such that the entire combined spectrum contains a signal measured under optimal conditions, the signal being located between the minimal SNR and the saturation level.

9. A spectrometric optical system, comprising an illumination system, and a light detection system, the illumination system comprising first and second illuminators operating with different wavelength ranges producing together light of a wavelength range of about 180-950 nm;

and a control unit connectable to the illumination and detection systems to control the operation of the illumination and detection systems, the control unit being configured to apply at least one preliminary measurement to an article and to select an optimal integration time range of the light detection system during which an actual measurement is to be applied to said article, said optimal integration time being that at which a required value of signal to noise ratio (SNR) of the measurements is obtainable.

10. The system of claim 9, comprising a beam combiner accommodated in optical paths of first and second light portions produced by, respectively, the first and second illuminators, to thereby combine these light portions into said light of the 180-950 nm wavelength range.

11. The system of claim 9, configured to allow passage of a second light portion, produced by the second illuminator, through the first illuminator, to thereby combine a first light portion, produced by the first illuminator, and the second light portion in a common optical path.

12. The system of any one of claim 9, wherein the first illuminator includes a Deuterium lamp, and the second illuminator includes a QTH lamp.

13. The system of claim 9, wherein the first illuminator includes a Deuterium lamp, and the second illuminator includes a Xe lamp.

14. The system of claim 9, wherein the first illuminator includes a Deuterium lamp, and the second illuminator includes a Metal-Halide lamp.