How to choose the right photodetector?
2021-11-09
According to the working principle and structure, photodetectors are usually divided into photodetectors and thermoelectric detectors. Photodetectors include vacuum photoelectric devices (photomultiplier tubes, etc.) and solid-state photodetectors (photodiodes, photoconductive detectors, CCDs, etc.).
● Photomultiplier tubes (PMT)
Photomultiplier tubes (PMT) are photodetectors with extremely high sensitivity, and also have the characteristics of fast response, low noise, and large cathode area (photosensitive surface).
● Photodiode
The working principle of photodiodes is mainly based on the photovoltaic effect. The photovoltaic effect is the effect that semiconductor materials generate electromotive force on PN junctions after absorbing light energy.
● Photoconductive detectors
Photoconductive detectors are photodetectors made using the photoconductive effect of semiconductor materials. The so-called photoconductive effect refers to a physical phenomenon in which the conductivity of the irradiated material changes due to radiation.
In the photoelectric test system, various detectors need to be selected according to actual needs, and special attention should be paid to the following issues:
1. Actual spectral measurement range, which is the first issue to pay attention to when selecting a photodetector;
2. Photomultiplier tubes are highly sensitive detectors with limited wavelength range (usually up to 900nm, some models can get more than 1000nm, but the price is usually very expensive), and require a high-stability high-voltage power supply when used;
3. Photovoltaic detectors have the characteristics of fast response and high sensitivity. Generally, a phase-locked amplifier is not required when using them, and they can be used when detecting weak signals. Select a phase-locked amplifier to improve the signal-to-noise ratio;
4. Photoconductive detectors have a slow response, and require signal light to be modulated when used, and need to be used with a phase-locked amplifier for signal detection. At the same time, pay attention to the selection of modulation frequency;
5. When selecting a detector, it is especially important to pay attention to the selection of a matching preamplifier to maximize the detection efficiency of the detector;
6. When selecting a TE-cooled detector, pay attention to the selection of the corresponding thermostat. The detector, thermostat and preamplifier must be selected separately according to needs;
7. Infrared detectors usually require cooling and use with a phase-locked amplifier.
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