Programmable deformation of thin liquid films using light projection
Diffractive optical elements (DOEs) enable precise manipulation of wavefronts and are widely used in a variety of optical systems. However, their fabrication relies on lithography or high precision machining processes that are long, expensive, and infrastructure-heavy.
We are developing a one-step rapid fabrication method that leverages the thermocapillary effect to shape thin liquid films into useful DOEs with sub-nanometeric surface roughness. Our system consists of a projection system, which illuminates any desired pattern onto the bottom of a fluidic chamber patterned with heat-absorbing pads. The heat induces surface tension gradients in the polymer-air interface, resulting in the polymer film deformation. The polymer is then photocured to yield a solid device.
We developed a theoretical model that provides the required projection pattern to achieve a desired topography. Based on this model, we demonstrate the fabrication of several DOEs, including phase masks for extended depth of field imaging, and for 3D localization microscopy.
Fabrication is completed in less than five minutes and requires no post-processing.
Operational principle of the thermocapillary fluidic shaping method. (a) Schematic illustration of the experimental setup. The setup is based on a shallow fluidic chamber filled with a thin layer of a curable polymer. The bottom surface of the chamber is a glass substrate patterned with an array of metal pads designed to absorb light in the visible spectrum. A desired illumination pattern is projected onto the surface using a DMD-based system. The inset describes the internal structure of the metallic pads. (b) A desired illumination pattern is projected onto the metal pads, which absorb the light and create a corresponding temperature field. Heat is transferred from the pads, through the thin liquid layer and to the liquid-air interface, leading to surface tension gradients that drive the thermocapillary effect, resulting in spatial deformations of the free surface. (c) Image of the solidified polymer after exposure to UV illumination.
Fabrication of a saddle point phase mask for three-dimensional localization microscopy. (a) Topography map of a saddle point phase mask microfabricated using standard lithography and ion etching processes. (b) The illumination pattern required for deforming the liquid film into a negative mold for the phase mask, as obtained from the inverse problem solution. (c) DHM measurement of the resulting solidified PDMS mask, cast on the mold fabricated by thermocapillary fluidic shaping.
Select Publications
Eshel R., Frumkin F., Nice M., Luria O., Ferdman B., Opatovski N., Gommed K., Shusteff M., Shechtman Y., and Bercovici M., (2022) “Programmable thermocapillary shaping of thin liquid films”, Flow, 2 E27.