Methods for collection, dark correction, and reporting of spectra from array detector spectrometers
Methods and systems for spectrometer dark correction are described which achieve more stable baselines, especially towards the edges where intensity correction magnifies any non-zero results of dark subtraction, and changes in dark current due to changes in temperature of the camera window frame are typically more pronounced. The resulting induced curvature of the baseline makes quantitation difficult in these regions. Use of the invention may provide metrics for the identification of system failure states such as loss of camera vacuum seal, drift in the temperature stabilization, and light leaks. In system aspects of the invention, a processor receives signals from a light detector in the spectrometer and executes software programs to calculate spectral responses, sum or average results, and perform other operations necessary to carry out the disclosed methods. In most preferred embodiments, the light signals received from a sample are used for Raman analysis.
1. A method of dark current correction in an instrument having a detector adapted to receive a dark exposure and a light spectrum from a sample, the method comprising the steps of:
(a) collecting a first set A of dark exposures with an exposure time D;
(b) collecting a first set of of signal exposures with an exposure time S;
(c) collecting a second set B of dark exposures with an exposure time D; wherein D represents a total exposure time of equal to or less than that of S/2;
(d) averaging or summing the results of (a) and (c), and scaling the result for an equivalent total dark exposure time equal to S;
(e) averaging or summing the result of (b); and
(f) subtracting the result of (d) from the result of (e) to deliver a dark-corrected collection;
(g) storing the result of (f) in a first-in/first-out buffer having N buffer elements;
(h) discarding set A and renaming set B as set A to re-use at least a portion of the dark exposure;
(i) repeating steps (b) through (g) until the buffer is full and, if a sample spectrum is desired:
(j) averaging or summing the N buffer elements to output the sample spectrum or, if a sample spectrum result is not desired:
(k) discarding the oldest element in the buffer and returning to step (h).
2. The method of claim 1 , including the step of repeating steps (b) through (f) until a desired signal-to-noise ratio is achieved by summing or averaging the multiple dark-corrected collections from (f).
3. The method of claim 1 , wherein the spectrometer is a Raman spectrometer, and the sample spectrum is a Raman spectrum.
4. The method of claim 1 wherein, in step (f), the dark-corrected collection is obtained by bracketing the light spectrum on both sides.
5. The method of claim 1 , wherein step (k) is repeated to improve the accuracy of the sample spectrum.
6. The method of claim 5 , wherein a sample spectrum is delivered after every dark-corrected collection.
7. The method of claim 5 , wherein a sample spectrum is not delivered after every dark-corrected collection.