It is well-known that conservation of phase-space volume or optical etendue leads to strict limits to concentration. Less well- known is the connection between entropy and etendue. Entropy has a logarithmic dependence on etendue in addition to the familiar linear dependence on heat. This trade-off permits, in principle, an exponential boost in concentration. Optical systems that make use of this possibility will be discussed.

© 2009 The Optical Society

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