Hohlraum

Not to be confused with Holuhraun.

In radiation thermodynamics, a hohlraum (German: [ˈhoːlˌʁaʊ̯m] ⓘ; a non-specific German word for a "hollow space", "empty room", or "cavity") is a cavity whose walls are in radiative equilibrium with the radiant energy within the cavity. First proposed by Gustav Kirchhoff in 1860 and used in the study of black-body radiation (hohlraumstrahlung),[1] this idealized cavity can be approximated in practice by a hollow container of any opaque material. The radiation escaping through a small perforation in the wall of such a container will be a good approximation of black-body radiation at the temperature of the interior of the container.[2] Indeed, a hohlraum can even be constructed from cardboard, as shown by Purcell's Black Body Box, a hohlraum demonstrator.[3]

In spectroscopy, the Hohlraum effect occurs when an object achieves thermodynamic equilibrium with an enclosing hohlraum. As a consequence of Kirchhoff’s law, everything optically blends together and contrast between the walls and the object effectively disappears.[4]

  1. ^ Harrison, Edward R. (March 1988). Black-Holes in History. Vol. 29. p. 87. Bibcode:1988QJRAS..29...87H. Retrieved June 28, 2024.
  2. ^ Allen, William H. (1965). Dictionary of Technical Terms for Aerospace Use. NASA SP-7. Vol. 7. NASA, Washington, D.C. p. 134. Bibcode:1965NASSP...7.....A. Retrieved June 27, 2024.
  3. ^ "Purcell's Black Body Box". Harvard Natural Sciences Lecture Demonstrations.
  4. ^ Mitchell, Herbert J.; Salvaggio, Carl (2003). "The MWIR and LWIR Spectral Signatures of Water and Associated Materials" (PDF). In Shen, Sylvia S.; Lewis, Paul E. (eds.). Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery IX. Vol. 5093. Proceedings of SPIE.