Issues

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1975

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April

  

Methodological notes


Another look at what is possible and impossible in optics

According to the Lagrange--Helmholtz law, no optical system can ever increase the brightness (and therefore the effective temperature) of a light beam. This limitation is frequently interpreted as a consequence of the second law of thermodynamics. Actually, thermodynamics imposes no limitations of practical importance on the possibilities of increasing the brightness of light beams: the decrease of the entropy of the light beam associated with the increase of its brightness can be compensated by a loss of a negligible fraction of the energy of the beam. The general discussions are illustrated by a number of specific examples.

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Fulltext is also available at DOI: 10.1070/PU1975v017n04ABEH004431
PACS: 42.60.Jf, 42.65.Re, 42.60.Lh (all)
DOI: 10.1070/PU1975v017n04ABEH004431
URL: https://ufn.ru/en/articles/1975/4/j/
Citation: Sobel’man I I "Another look at what is possible and impossible in optics" Sov. Phys. Usp. 17 596–598 (1975)
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Оригинал: Собельман И И «Еще раз о возможном и невозможном в оптике» УФН 113 701–705 (1974); DOI: 10.3367/UFNr.0113.197408g.0701

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