Photodetectors are usually divided into photodetectors and thermoelectric detectors according to their working principles and structures. Photodetectors include vacuum photodetectors (photomultiplier tubes, etc.) and solid-state photodetectors (photodiodes, photoconductive detectors, CCD, etc.).



Photomultiplier tubes (PMT)
Photomultiplier tube (PMT) is a highly sensitive light detection device, which also has characteristics such as fast response, low noise, and a large area cathode (photosensitive surface).

● Photodiode
The working principle of photodiodes is mainly based on the photovoltaic effect. The photovoltaic effect is the effect of generating electromotive force on the PN junction of semiconductor materials after absorbing light energy.

● Photoconductive detector
A photoconductive detector is a type of photodetector device that utilizes the photoconductive effect of semiconductor materials. The so-called photoconductivity effect refers to a physical phenomenon in which the conductivity of the irradiated material changes due to radiation.



In optoelectronic testing systems, various detectors need to be selected according to actual needs, with special attention paid to the following aspects:
1. The actual spectral measurement range is the first thing to pay attention to when choosing a photodetector;
2. Photomultiplier tubes are highly sensitive detectors with a limited wavelength range (usually up to 900nm, some models can achieve 1000nm or more, but the price is usually expensive), and require a high stability high-voltage power supply when used;
3. Photovoltaic detectors have the characteristics of fast response and high sensitivity, and generally do not require a lock-in amplifier when used. When detecting weak signals, a lock-in amplifier can be selected to improve the signal-to-noise ratio;
4. The response of the photoconductive detector is slow, and when using it, signal light modulation is required, and a lock-in amplifier is needed for signal detection. At the same time, attention should be paid to the selection of modulation frequency;
5. When selecting a detector, it is particularly important to pay attention to selecting the matching preamplifier in order to maximize the detection efficiency of the detector;
6. When selecting TE refrigeration type detectors, attention should also be paid to the corresponding temperature controller selection. The detector, temperature controller, and preamplifier should be selected separately according to needs;
7. Infrared detectors typically require cooling and use in conjunction with lock-in amplifiers.