Everything You Need to Know About IR Detectors

Detectors for infrared light are referred to as Infrared detectors. Some of them are based on sensing temperature rises which are usually caused by the absorption of infrared light. In contrast, others are photodetectors that increase sensitivity in a long-wavelength area. Laser viewing cards may be regarded as infrared detectors. Here are some of the things you need to know about IR detectors.

Infrared Photodetectors

Infrared photodiodes

Ordinary silicon photo bodies can be used for the short-wavelength since their responsivity drops depending on how thick the active region is. Semiconductor materials that contain lower gap energy are essential for longer wavelengths.

Infrared Photoconductive Detectors

Lead salt detectors can detect infrared light at high wavelengths. Epitaxial growth is not fabricated with such devices, even though they contain a P-n junction. This is because they are not photodiodes but photoconductors. Lead salt detectors perform better with cooled detectors, although they can also be used at room temperature. Apart from improving sensitivity, cooling also reduces the dark current. In addition to that, to detect light with longer wavelengths, and band gap energy is reduced.

Hazardous substances are contained in some of these infrared materials. This highly restricts their use due to European regulations. However, specific applications have been set up for temporary exceptions in places where substitutes are hard to find.

Thermal Infrared Detectors

Thermal detectors respond to an increase in temperature resulting from the absorption of incoming infrared light instead of detecting protons. They are made up of different technologies:

Pyroelectric Detectors

They are pyroelectric detectors that generate a small electric voltage pulse in regards to a temperature gradient because they are based on Ferroelectric materials. These detectors can measure the pulse energy of a Q-switched laser.


A bolometer sensor is made up of a thin infrared-absorbing plate that is draped with two different electrodes. The electrical resistance of the plate can be measured depending on the temperature. The temperature of the plate relaxes towards the sink of the temperature without incorporating an incoming infrared light. If the temperature readings do not remain constant, they will eventually be corrected depending on the temperature substrate. Their temperature can be stabilized since they are usually operated at room temperature.

A trade-off between Sensitivity and Bandwidth

Sensitivity and bandwidth are constantly exchanged between themselves when it comes to thermal detectors. They can be understood after measuring its temperature capacity. Temperature rise and bandwidth are induced while ignoring the thermal capacity of other things:

A high thermal resistance slows down the detector since the thermal time proportional to the heat capacity is constant and proportionate to the thermal resistance.

To obtain high sensitivity, a high thermal resistance is essential. Therefore the measurement signal and the temperature rise should be proportional to the thermal resistance. Additionally, it is advisable to use a small absorber for the incident light to be focused on it.

Thermal noise is limited in the form of temperature changes. The standard deviation is inversely proportional to the square root of the thermal capacity. Thus the standard deviation of the temperature can be shown easily. However, other noise sources such as those of the temperature sensor may still be limited.