Definition of blackbody source

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Photonics Dictionary

blackbody source: A blackbody source, often simply referred to as a blackbody, is a theoretical or practical physical object that absorbs all electromagnetic radiation incident upon it and emits radiation in a characteristic manner determined solely by its temperature. In simpler terms, it is an object that absorbs all radiation that falls on it and emits radiation according to its own temperature.

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Key characteristics of a blackbody source include:

Perfect absorption: A blackbody absorbs all incident radiation across the entire electromagnetic spectrum, regardless of wavelength or frequency. As a result, no radiation is reflected or transmitted through a blackbody.

Thermal equilibrium: A blackbody is in thermal equilibrium with its surroundings, meaning that its temperature remains constant over time. Any radiation absorbed by the blackbody is re-emitted as thermal radiation.

Spectral radiance: The intensity and spectral distribution of radiation emitted by a blackbody depend solely on its temperature and follow a characteristic curve known as the blackbody radiation curve, which is described by Planck's law. At higher temperatures, a blackbody emits more radiation at shorter wavelengths, shifting the peak of its emission towards shorter wavelengths.

While a true blackbody is an idealized concept, certain materials and objects approximate blackbody behavior to varying degrees. Examples of practical blackbody sources include heated cavities with small openings, such as a small hole in a furnace or a hollow cavity with a highly absorbing interior surface. These sources can be used in various applications, including calibration of temperature sensors, thermal imaging systems, and spectroscopy.