Quantum Detectors

Photon detectors, also known as quantum detectors, operate on the basis of the photoelectric effect. When photons of infrared radiation are absorbed, they cause electrons in the semiconductor material to move to higher energy levels. The return of these electrons to their ground state produces an electrical signal, which is then measured. Quantum detectors include photoconductive cells and photovoltaic cells and can also result in a change in electric resistance. These highly sensitive detectors have rapid response times, which makes them suitable for applications requiring fast detection and precise measurements.

The key difference between quantum and thermal detectors is their faster response to absorbed radiation. The temperature of the sensitive element of a thermal detector changes relatively slowly. The time constants of thermal detectors are usually greater than those of quantum detectors. Generally, the time constants of thermal detectors can be measured in milliseconds, while those of quantum detectors can be measured in nanoseconds or even microseconds.

For infrared imaging, quantum detectors are typically used in research applications, remote sensing, and high-speed thermal imaging. Cooled infrared cameras usually use quantum detectors and cooling systems to reduce thermal noise, making the camera more expensive and requiring more maintenance. Despite the rapid developments in the field of quantum detectors, there are still many applications where thermal detectors are more suitable.

For pyrometry, quantum detectors have become significant in short wavelength applications, as infrared photodiodes in these cases often do not require additional cooling. However, there are still applications where thermal detectors are used.