Spectrometer system for optical reflectance measurements

A method of controlling a spectrum of light emitted from a heated filament, the method comprising:

• supplying electrical current from a power supply to heat the filament;
• sensing a current flowing through the filament;
• sensing a voltage drop across the filament;
• comparing a ratio of the sensed voltage drop and the sensed current with a predetermined value;
• and
• controlling the current or the voltage drop to cause the ratio to equal the predetermined value.

A spectrometer system comprising:

• a light source;
• a spectrograph;
• an first optical beam path for guiding light from the light source to a sample;
• a second optical beam path for guiding light from the light source to the spectrograph;
• a third optical beam path for guiding light reflected from the sample to the spectrograph;
• a shutter for blocking and unblocking the light in the first beam path from the sample and for blocking and unblocking light in the second beam path from the spectrograph;
• and
• a processor adapted for analyzing light spectra from light guided into the spectrograph and adapted for correcting the spectra for a dark current in the system based on spectra recorded when both the first and second optical beam paths are blocked and adapted for correcting the spectra for temporal changes in the spectrum of the light source based on a plurality of spectra recorded at different times when light is guided into the spectrograph along the second beam path.

A method for correcting a spectrum measured by a spectrometer system having a spectrograph and a light source for illuminating a sample with light output from the light source, the method comprising:

• recording a reference spectrum, Ro(λ), from a reference sample having a known reflectivity spectrum when light from the light source is shined on the reference sample;
• recording an initial lamp spectrum, Lo(λ), of the light output from the light source at an initial time when light from the light source is shined into the spectrograph;
• recording a subsequent lamp spectrum, Lt(λ), of the light output from the light source at a time later than the initial time when light from the light source is shined into the spectrograph;
• recording a spectrum from a test sample, S(λ);
• correcting the spectrum from the test sample using data from the reference spectrum, the initial lamp spectrum, and the subsequent lamp spectrum, to produce a corrected spectrum;
• and
• outputting the corrected spectrum.