The main advantage of cooling a photodetector is to reduce the thermally generated dark current. The dark current represents an intrinsic source of noise that depends on the temperature of the sensor. This unwanted current accumulates over the integration time of the exposure and thus is more important for long integration times. In applications such as
and scientific spectroscopy, the amount of dark current can make the difference between good results and no results at all. Therefore, lowering the sensor temperature and stabilizing it often provides a significant improvement to
. Photo detectors used in a spectrophotometer are composed of many small photodiodes called pixels that consist of light sensitive semi-conductor materials such as silicon [Si] or indium gallium arsenide [InGaAs].
These photodiodes convert photons to an electrical signal, which is proportional to the light exposure. The sensors can be categorized into 1D or 2D photodetector arrays, depending on the geometrical arrangement of pixels. A silicon-based Charge Coupled Device [CCD] is a highly sensitive photodetector, capable of detection from the Ultraviolet
[UV] to the near-infrared
[NIR] region of the spectrum. Indium gallium arsenide [InGaAs] is another common sensor type which provides superior photosensitivity in the NIR region above 1,100nm. The performance of both sensor types is dependent upon many factors, including response time, sensitivity, spectral response, and temperature of operation. Cooling [albeit not to cryogenic levels] can be required to reduce the dark current and provide signal-to-noise ratios [SNR] needed for many advanced spectroscopy applications. For example, the noise performance of the CCD could be reduced from hundreds of electrons per pixel and per second integration time at room temperature to only several electrons at -20 degrees Celsius. In higher scan rate applications, the performance improvement from a cooled sensor also can be substantial. Reduced dark current in combination with increased stability and repeatability directly meets the requirements of applications involving fast scan rates such as industrial sorting and characterization of pulsed light sources.High Speed spectrometer
systems by tec5 provide the fastest continuous sensor operation available, equipped with 16-bit ADCs and 10 MHz readout. Depending on the sensor size, this enables scan rates up to more than 15,000 spectra per second for demanding applications.
To perform cooling with the Peltier-tc, photodiode arrays must be equipped with a built-in Peltier element, a thermistor temperature sensor and a sensor heat sink.