Optical force regulation with nanostructured materials
thesisposted on 10.03.2020 by Li-Fan Yang
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
The use of light to control mechanical systems is of broad importance in science and technology. From Maxwell’s theory, the maximum optical pressure on a mirror is twice the average incident power density divided by the velocity of light. Here it is experimentally demonstrated that, with a specially designed nanostructured membrane, the optical pressure substantially exceeds that on a perfect mirror. Enhanced pressure is demonstrated by deflection measurement of a patterned gold film on a silicon nitride membrane, in conjunction with a model and with established error bounds to draw definitive conclusions. The enhancement of the net optical pressure with nanostructured material over that on a perfect mirror can be understood as being due to an asymmetric cavity effect within a modest quality factor regime, and this is illustrated using a simple one-dimensional model. Therefore, carefully harnessing the photon confinement in nanostructured material leads to pressure enhancement.
The physical basis of a net pulling force on a structure is presented. Whether there is a pushing or a pulling pressure can be regulated by excitation of a surface wave on the front or back side of a nanostructured metal film. This can be achieved through geometrical and material design, and it is shown that pushing or pulling with a single structure, depending on wavelength, is possible. Furthermore, an enhanced pulling pressure can also be achieved in a simple all-dielectric silicon-based system.Various applications will benefit from optomechanics with pushing or pulling achieved by control of the characteristic of the incident light.