How to select the appropriate photodetector?
According to the working principle and structure, photodetectors are generally divided into photoelectric detectors and thermoelectric detectors. Photoelectric detectors include vacuum photoelectric devices (photomultiplier tubes, etc.) and solid photoelectric detectors (photodiodes, photoconductive detectors, CCD, etc.).
● Photomultiplier tubes (PMT)
Photomultiplier tube (PMT) is a kind of light detection device with extremely high sensitivity, and has the characteristics of fast response, low noise, large area cathode (photosensitive surface), etc.
The working principle of the photodiode is mainly based on the photovoltaic effect. Photovoltaic effect is the effect that semiconductor materials produce electromotive force on PN junction after absorbing light energy.
● Photoconductive detector
The photoconductive detector is a kind of light detection device made of the photoconductive effect of semiconductor materials. The so-called photoconductivity effect refers to a physical phenomenon that changes the conductivity of the irradiated material caused by radiation.
In the photoelectric test system, various detectors need to be selected according to the actual needs, especially the following aspects:
1. The actual spectrum measurement range, which is the first problem to pay attention to when selecting optical detectors;
2. The photomultiplier tube is a highly sensitive detector with a limited wavelength range (usually up to 900 nm, some models can get more than 1000 nm, but the price is usually very expensive), and requires a high voltage power supply with high stability when used;
3. Photovoltaic detectors have the characteristics of fast response and high sensitivity. Generally, phase-locked amplifiers are not required for use. When detecting weak signals, phase-locked amplifiers can be selected to improve the signal-to-noise ratio;
4. The photoconductive detector has a slow response. When it is used, the signal light is required to be * * * modulated, and it needs to be matched with a phase-locked amplifier to detect the signal. At the same time, attention should be paid to the selection of modulation frequency;
5. When selecting detectors, it is particularly necessary to pay attention to the selection of matching preamplifiers in order to maximize the detection efficiency of detectors;
6. When selecting TE refrigeration type detector, pay attention to the selection of corresponding temperature controller. The detector, temperature controller and preamplifier should be selected separately according to needs;
7. Infrared detectors usually need refrigeration and use with phase-locked amplifiers.