dark current
Dark Current
Dark current occurs because random thermal fluctuations provide enough energy to lift electrons across the band gap, forming electron-hole pairs. Electron-hole pairs are separated by a local electric field, and free electrons are stored in the pixel well. A spectrometer cannot distinguish electrons generated by thermal fluctuations from electrons generated by incident photons, so they appear as noise in the spectrometer's spectrum. The rate at which electron-hole pairs are generated at a given temperature is called dark current. Shot noise causes fluctuations in the dark current, forming dark noise. Because the dark current is formed by continuously generated electron-hole pairs, a longer integration time will result in a greater number of electrons required to form the dark current. Thermoelectric cooling of the CCD can significantly reduce dark current and dark noise. In practice, high-performance spectrometers are usually cooled to such an extent that the dark current is insignificant during a typical integration interval. Using TEC refrigeration can greatly reduce the dark current.
dark noise
Dark Noise
Dark noise is formed due to statistical changes in the number of thermally generated electron-hole pairs within the CCD's silicon structure. Dark noise is independent of the signal generated by the photons, but strongly dependent on the temperature of the device. At a given CCD temperature, the rate of electron generation is called dark current. Dark noise is a form of shot noise that is directly related to dark current, and its magnitude is equal to the square root of the number of electrons produced during the integration time. Thermoelectric cooling of the CCD can significantly reduce dark current and dark noise. In spectrometers, where the photon energy is very low and dark noise can easily mask the useful signal, thermoelectric cooling can reduce the dark current to negligible levels over the entire integration interval.
dark spectrum
Dark Spectrum
The dark spectrum is the wavelength value of a series of spectra within a given integration time of the spectrometer in the absence of incident light (neither from the sample nor from surrounding ambient light sources). Dark spectra were used to correct for baseline regression and to fix pattern noise. The dark spectrum is also referred to as "dark signal" in other ocean optics literature. It is worth noting that the dark spectrum is different from the background spectrum, which represents the signal of the spectrometer when there is no reference light source.
