Dissertation Defense: Spencer Ketchum, "Characterization of optical systems and materials for applications in solar concentration, radar emulation, and computer holography"

    Tuesday, August 2, 2022 - 3:00pm

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    Much of optics and photonics is concerned with the management of light, more specifically, the management or modification of an incident light field. This could include redirecting or shaping the light or managing how light scatters off an object. This dissertation looks at light management and characterization in three sets of projects involving solar concentrators, radar emulation, and computer holography.

    The design and characterization of three different solar concentrator systems using a combination of concentrated photovoltaics (CPV) and concentrated solar power (CSP) are presented. These systems use either large concentration (~160x) and high efficiency multi-junction photovoltaics for high electricity generation or solar spectrum splitting to divide the solar spectrum between applications to optimize usage. These applications include simultaneous electricity and heat generation for solar desalination and simultaneous electricity generation and visible translucency for greenhouse integrated PV.

    Another application of light management is radar scatter from complex structures. When structures are highly complex, computer simulations of radar scatter become very computationally expensive. One method of characterizing radar scatter is to physically emulate the system by scaling the structure size and measuring scatter using an equally scaled wavelength. Historically, this technique has mostly been limited to small scale factors <100. We extend the scale factor to 10,000-100,000, scaling Ka through S-band radar signals down to the optical/near infrared regime. 3D Models for this scale factor can be rapidly fabricated using two-photon lithography (TPL). In order to emulate different dielectric materials, the optical properties of the TPL resin at the scaled wavelength must match the unscaled system. The refractive index of the resin can be tuned by doping the material with high index nanoparticles like TiO2. Synthesis and application of such a material for TPL is demonstrated by 3D printing and characterizing micro lenses.

    Lastly, a new MEMS based phase-only spatial light modulator technology is evaluated for use in computer holography. Diffraction efficiency characteristics of the device are simulated and measures across the visible spectrum. The device is also evaluated for projecting computer generated holograms and the resulting image quality is analyzed.