Methods for collection, dark correction, and reporting of spectra from array detector spectrometer
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 a spectrometer used to receive and analyze light from a sample, the method comprising the steps of:
providing a spectrometer camera having a region designated for signal collection, and one or more regions not designated for signal collection, and a processor operative to perform the following functions:
(a) receiving and storing data representative of a true dark (TD) spectrum using the region of the camera designated for signal collection, but without light entering the camera, and receiving and storing data representative of an unilluminated dark (UD) spectrum using a region of the camera not designated for signal collection but with light from the sample entering the camera;
(b) deriving a mathematical relationship between TD and UD;
(c) simultaneously receiving and storing data representative of a light spectrum from a sample using the region of the camera designated for signal collection, and receiving and a new unilluminated dark (new UD) using a region of the camera not designated for signal collection;
(d) calculating a new TD as a function of new UD; and
(e) subtracting new TD from the data representative of the light spectrum to generate a result.
2. The method of claim 1 , wherein the spectrometer is a Raman spectrometer, and the light from the sample includes a Raman spectrum.
3. The method of claim 1 , including the steps of:
storing the result of step (e) in a buffer;
repeating steps (c) through (e) until the buffer is full, then:
(g) summing or averaging the elements of the buffer;
(h) generating a result;
(i) deleting the oldest element in the buffer; and
(j) repeating steps (c) through (i) until a desired number of spectra have been collected.
4. The method of claim 3 , wherein the spectrometer is a Raman spectrometer, and the light from the sample includes a Raman spectrum.
5. The method of claim 1 , wherein TD or UD are measured in conjunction with one or more spectrometer camera detector states or detector parameters.
6. The method of claim 5 , wherein the one or more detector states or detector parameters include detector temperature or exposure time.
7. The method of claim 1 , including the following step:
(f) repeating steps (c) through (e) until a desired number of spectra have been collected.
8. The method of claim 1 , wherein the region of the camera not designated for signal collection is inbetween signal fiber images on a 2-dimensional CCD array.
9. The method of claim 1 , wherein the region of the camera not designated for signal collection includes non-illuminated regions of a linear array detector.