Thermal, Density, and Other Nonelectronic Nonlinear Mechanisms

In Chapter 5 we discussed how the electrostrictive effect gives rise to density fluctuations in liquid crystals, which are manifested in frequency shifts and broadening in the spectra of the scattered light. In absorbing media, density fluctuations are also created through the temperature rise following the absorption of the laser. The nature of optical absorption in hquid crystals, as in ar r other material, depends on the laser wavelength. 

Under intense laser illrrmination, two- and mirltiphoton absorption processes will occnr, as depicted in Figrrre 9.3. In this case a so-called nortabsorbing material in the single-photon pictrrre outlined previottsly cotrld actrrally be quite absorptive, if the two- or mrrltiphoton process corresponds to a real transition to an excited state. 

The equation describing the rate of change of energy density u is given by 

The first term on the right-hand side denotes the rate of absorption of the light energy, the second term denotes the rate of energy diffusion and the third term describes the 

Liquid Crystals, Second Edition By lam-Choon Khoo Copyright 2007 John Wiley Sons, Inc. 

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Thermal, Density, and Other Nonelectronic Nonlinear Mechanisms... 

THERMAL, DENSITY, AND OTHER NONELECTRONIC NONLINEAR MECHANISMS... 

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