Dispersive near-infrared spectrometer with automatic wavelength calibration

Abstract

The present invention is a dispersive, diffraction grating, NIR spectrometer that automatically calibrates the wavelength scale of the instrument without the need for external wavelength calibration materials. The invention results from the novel combination of: 1) a low power He—Ne laser at right angles to the source beam of the spectrometer; 2) a folding mirror to redirect the collimated laser beam so that it is parallel to the source beam; 3) the tendency of diffraction gratings to produce overlapping spectra of higher orders; 4) a “polka dot” beam splitter to redirect the majority of the laser beam toward the reference detector; 5) PbS detectors and 6) a software routine written in Lab VIEW that automatically corrects the wavelength scale of the instrument from the positions of the 632.8 nm laser line in the spectrum.

1 . A dispersive, diffraction grating NIR spectrometer with the improvement being automatic calibration of the wavelength scale of the instrument without the need for external wavelength calibration means. 
   
   
       2 . The spectrometer of  claim 1 , the improvement further defined as comprising a low power laser at right angles to a source beam of the spectrometer. 
   
   
       3 . The spectrometer of  claim 1 , the improvement further defined as comprising a low power He—Ne laser at right angles to a source beam of the spectrometer. 
   
   
       4 . The spectrometer of  claim 1 , the improvement further defined as comprising a low power He—Ne laser at right angles to a source beam of the spectrometer where the He—Ne laser emits a collimated laser beam with a wavelength of 632.8 nm. 
   
   
       5 . The spectrometer of  claim 1 , the improvement further defined as comprising a mirror to redirect a laser beam so that it is parallel to a source beam. 
   
   
       6 . The spectrometer of  claim 1 , the improvement further defined as comprising a folding mirror to redirect a He—Ne laser beam so that it is parallel to a source beam. 
   
   
       7 . The spectrometer of  claim 1 , the improvement further defined as comprising a beam splitter to divert the majority of a laser beam toward a reference detector. 
   
   
       8 . The spectrometer of  claim 1 , the improvement further defined as comprising a “Polka-dot” beam splitter to divert the majority of a He—Ne laser beam toward a reference detector. 
   
   
       9 . The spectrometer of  claim 1 , the improvement further defined as comprising a beam splitter to divert the majority of a laser beam toward a PbS reference detector. 
   
   
       10 . The spectrometer of  claim 1 , the improvement further defined as comprising a “Polka-dot” beam splitter to divert the majority of a He—Ne laser beam toward a PbS reference detector. 
   
   
       11 . The spectrometer of  claim 1 , the improvement further defined as comprising a PbS sample detector. 
   
   
       12 . The spectrometer of  claim 1 , the improvement further defined as comprising a software routine written in LabVIEW that automatically corrects the wavelength scale of the instrument. 
   
   
       13 . The spectrometer of  claim 1 , the improvement further defined as comprising a software routine written in LabVIEW that automatically corrects the wavelength scale of the instrument from the positions of the 632.8 nm laser line in a spectrum. 
   
   
       14 . The spectrometer of  claim 1 , the improvement further defined as comprising a low power He—Ne laser at a right angles to a source beam where a He—Ne laser emits a collimated laser beam with a wavelength of 632.8 nm; a folding mirror to redirect the He—Ne laser beam so that it is parallel to the source beam; a “polka dot” beam splitter to divert the majority of the laser beam toward a PbS reference detector; a PbS sample detector; a software routine written in LabView that automatically corrects the wavelength scale of the instrument from the positions of the 632.8 nm laser line in a spectrum. 
   
   
       15 . A method for improving the calibration capabilities of a NIR spectrometer comprising:
 obtaining an enhanced calibration set of NIR spectra by improving a dispersive, diffraction grating NIR spectrometer so that it automatically calibrates the wavelength scale of the spectrometer without the need for external wavelength calibration means.   
   
   
       16 . The method of  claim 15  further comprising obtaining a low power laser and placing said laser at right angles to a source beam of the spectrometer. 
   
   
       17 . The method of  claim 15  further comprising obtaining a low power He—Ne laser and placing said laser at right angles to a source beam of the spectrometer. 
   
   
       18 . The method of  claim 15  further comprising obtaining a low power He—Ne laser and placing said laser at right angles to a source beam of the spectrometer where the He—Ne laser emits a beam with a wavelength of 632.8 nm. 
   
   
       19 . The method of  claim 15  further comprising obtaining a mirror and redirecting a laser beam with said mirror so that said mirror beam does not block a source beam from a quartz halogen lamp of the spectrometer and said laser beam is parallel to said source beam. 
   
   
       20 . The method of  claim 15  further comprising obtaining a folding mirror and redirecting a laser beam with said mirror so that said folding mirror does not block a source beam from a quartz halogen lamp of the spectrometer and said laser beam is parallel to said source beam. 
   
   
       21 . The method of  claim 15  further comprising obtaining a folding mirror and redirecting a low power collimated He—Ne laser beam with said mirror so that said folding mirror does not block a source beam from a quartz halogen lamp of the spectrometer and said laser beam is parallel to said source beam. 
   
   
       22 . The method of  claim 15  further comprising obtaining a beam splitter and diverting the majority of a laser beam with said beam splitter toward a reference detector. 
   
   
       23 . The method of  claim 15  further comprising obtaining a “Polka-dot” beam splitter and diverting the majority of a laser beam with said beam splitter toward a PbS reference detector. 
   
   
       24 . The method of  claim 15  further comprising obtaining a PbS sample detector and positioning said PbS sample detector such that a source beam light strikes it after passing through a sample cell holder. 
   
   
       25 . The method of  claim 15  further comprising obtaining and installing a computer software routine that automatically corrects the wavelength scale of the spectrometer. 
   
   
       26 . The method of  claim 15  further comprising obtaining and installing a software routine written in LabVIEW that automatically corrects the wavelength scale of the spectrometer. 
   
   
       27 . The method of  claim 15  further comprising obtaining and installing a software routine written in LabVIEW that automatically corrects the wavelength scale of the spectrometer from the positions of 632.8 nm laser line in a spectrum. 
   
   
       28 . The method of  claim 15  further comprising:
 obtaining a He—Ne low power laser;   placing said laser at right angles to a source beam of the spectrometer where the He—Ne laser emits a collimated beam with a wavelength of 632.8 nm;   obtaining a folding mirror; redirecting the low power collimated He—Ne laser beam with said mirror so that said folding mirror does not block the source beam from a quartz halogen lamp of the spectrometer and said laser beam at 632.8 nm is parallel to said source beam;   obtaining a “Polka-dot” beam splitter; diverting the majority of the laser beam with said “Polka-dot” beam splitter toward a PbS reference detector;   obtaining a PbS sample detector; positioning said PbS sample detector such that the source beam light strikes it after passing through a sample cell holder;   obtaining and installing a software routine written in LabVIEW that automatically corrects the wavelength scale of the spectrometer from the position of 632.8 nm laser line in a spectrum.