Light pressure on chiral sculptured thin films

Sculptured thin films (STFs) are porous thin films manufactured by physical vapor deposition processes, and possess a morphology that is engineered at the nanoscale. When a circularly polarized plane wave is obliquely incident on a chiral STF, the Maxwell stress dyadic exhibits a decreasing periodic variation across the thickness of the film. Normal and tangential surface tractions exist on the two faces of the chiral STF, as well as a net normal pressure across the film. These stresses are affected by the incidence angle of light, and are maximized when (i) the incident plane wave and the chiral STF are co-handed, (ii) the wavelength falls within a regime called the Bragg regime, (iii) the ratio of film thickness to the structural period of the chiral STF reaches a saturation value, (iv) the deviation from normal incidence is small, (v) the loss factor in the chiral STF is as low as possible, and (vi) the vapor incidence angle is optimally chosen during film deposition.