Fast reconfigurable liquid optical interface: Investigation of higher harmonics in the periodic liquid surface wrinkle

We have recently reported a novel approach to producing voltage programmable optical devices in which static wrinkles are created at the surface of a thin film of oil [Nature Photonics 3(7), 403 (2009)]. The oil coats a 2d electrode pattern and dielectrophoretic forces created from the non-uniform fringing electric field profiles near to the electrodes determine how this pattern is "imprinted" at the remote oil/air interface. Sinusoidal wrinkles have been created on the surface of decanol oil with pitch lengths of between 20 and 240 micrometers and have been rapidly switched on in less than 40 microseconds. Non-sinusoidal surface wrinkles with higher harmonics appear when electrodes with the larger pitches are used in conjunction with an oil that has a lower dielectric constant, for example hexadecane. It is found that the higher Fourier components of the shape of the periodic wrinkle decay faster than the fundamental component as the thickness of the oil film is increased.