If there are several minutes in between two spectra for instance, the detector temperature can already have changed, changing the dark current. Often, the closer in time the two spectra are taken the better reference the dark measurement forms. have the same integration time and detector temperature. Obviously for the best signal to noise ratio it is always better to have no background light.Ī suitable dark measurement is always measured at the same conditions as the real measurement. To have that work properly the background has to be the same in dark and light measurement. To remove the dark current contribution it is thus important to use the same integration time for dark and light measurements and also it is important to have the temperature of the detector the same in both measurements.īackground light is also removed when using dark subtraction. The dark current contribution is accumulative it rises linearly with integration time. Dark current therefore rises if the temperature rises (See also our Technical Note on cooled detectors). The baseline is not always stable in time it can show fluctuations and drift for instance due to temperature changes.Ĭontrary to the real signal that originates from electrons absorbing one photon, the dark current of the detector originates from electrons that acquire energy in a thermal process.
This baseline is thus not a real signal and can in fact often be set by the user. The baseline originates from a voltage that is added to the signal to allow a correct conversion of the analog signal to a digital signal by the electronics. Thus by subtracting the dark measurement you get closer to observing the real signal you are interested in. It can in also be used to get rid of background light.It removes the dark current contribution from the measurement.It removes the baseline from the measurement.There are three main reasons to subtract a dark measurement: High Pressure Liquid Chromatography (HPLC)įigure 1, schematic description of dark subtraction.Laser-Induced Breakdown Spectroscopy (LIBS).
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