Linear and non-linear photo-induced deformations of cantilevers
Glassy and elastomeric nematic networks with dye
molecules present respond to illumination by reversibly straining because their order parameter is reduced. Elastomers may respond with huge strains and possibly also with director rotation. Appreciable absorption means strain decreases with depth into a cantilever, leading to bend -- the basis of micro-opto-mechanical systems (MOMS). Experimentally, bend can occur even when Beer's law
suggests a tiny penetration of light into a heavily dye-doped system. We model general non-linear absorptive processes behind deep penetration into dyes, and also the resultant opto-elastic processes in dye-loaded cantilevers. Bleaching of the active dye species allows deeper penetration of strong beams. When incident light of high intensity gives optimal bending, for a given cantilever thickness, there are three neutral surfaces. We discuss
the form of the strains arising when only order parameter reduction is considered. Compressive strains aid director rotation which may be important in elastomeric cantilevers. In practice non-linear absorptive effects are probably important since heavily dye-doped optical cantilevers are commonly used.