This article is cited in 3 papers

METHODOLOGICAL NOTES

Another look at what is possible and impossible in optics

I. I. Sobel'man

P. N. Lebedev Physical Institute, the USSR Academy of Sciences, Moscow

Abstract: 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.

UDC: 535.8

PACS: 42.60.Jf, 42.65.Re, 42.60.Lh

DOI: 10.3367/UFNr.0113.197408g.0701

 English version: Physics–Uspekhi, 1975, 17:4, 596–598