Radiometry and non-coherent sources

The performance of an optronic system depends on the numerous parameters and components which, from the source to the user, make up what is known as the optronic chain, and generally reflects the system's ability to collect and then make the best use of the desired signal. To achieve this, system design must be based on a thorough understanding of each element in the chain, and in particular of the initial link, the optical source, which is the source of the information.

All optical radiation results from the transformation of various energies (thermal, electrical, electronic, mechanical, chemical, nuclear, even optical) into light energy. The propagation of this light energy is interpreted either (wave theory) in the form of electromagnetic waves with wavelengths ranging from a few hundredths to a few hundred micrometers, or (corpuscular theory) by the movement of particles, photons, whose individual energy ranges from 10 ^–22 to 10 ^–17 J.

In many applications, such as observation, imaging, photography, astronomy, etc., the optical source emits autonomously, without any intervention from the optronic system (a so-called passive system). In other applications, such as optical telecommunications, the active system uses its own artificial source to create, modify or amplify the phenomenon to be exploited. In all cases, it is essential for the designer to know and/or specify the characteristics of the radiation to be detected, as these are what condition the entire optronic chain.

First, we review the fundamental laws of radiometry, then present the main families of conventional sources: incandescent (or thermal), then luminescent.

Laser sources are covered in a separate article in this section.