Rapid Prototyping of Metalenses using a Focused Beam

Michael Shares

Abstract


Metalenses offer an alternative to typical glass lenses possessing unique physical characteristics such as negative indices of refraction, that enables sub-diffraction limited focusing and lens uses. DuPont Kapton film, a cheap polyimide, may be altered to demonstrate these properties using individual unit cells to create alternating dielectric, inductive, and capacitive layers combined to produce a metalens. Current processes achieve unit cells with line widths as narrow as 15µm, expanding the frequency range of these lenses into the microwave spectrum. Our team seeks to find whether using a high-powered, focused laser beam, using pyrolysis, provides a viable rapid metalens prototyping procedure for even higher frequencies by producing lines thinner than 15µm. We designed a multiple-lens system to focus a 532 nm beam to a near diffraction limited spot size of 1-2µm. Matlab script controlled two Thorlabs Z825B Servos, a Lambda Sutter SC shutter system, and a Physike Instrument E-664 servo to automate the burn process. We controlled the incident power on the Kapton using a Thorlabs ½-λ plate and beamsplitter, monitored by a power meter. Since a tightly focused beam has an extremely short Rayleigh Range, we first conducted experiments to empirically optimize the focus of the beam and maximize intensity delivered to the Kapton. After finding the optimal focus, experiments conducted at different incident powers and shutter timings found an optimal combination of 13ms and 375mW, producing the smallest, carbonized spots our team found to date at 2.29µm. To prevent warping, which moves the Kapton out of the Rayleigh Range; we believe repeated spots are best to produce a composite, conducting line. Previous research on this project produced conducting lines that correlated strongly with the burn spot size, suggesting that conducting lines of less than 15µm are obtainable with continued work and our current system.


Keywords


Metalenses, Pyrolization, Kapton Polyimide

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