Nicholas A. Charipar

By combining the enhanced photosensitive properties of zinc oxide nanoparticles and the excellent transport characteristics of graphene, UV-sensitive, solar-blind hybrid optoelectronic devices have been demonstrated. These hybrid devices offer high responsivity and gain, making them well suited for photodetector applications. Here, we report a hybrid ZnO nanoparticle/graphene phototransistor that exhibits a responsivity up to 4 × 10⁴ AW⁻¹ and gain of up to 1.3 × 10⁵ with high UV wavelength selectivity. ZnO nanoparticles were synthesized by pulsed laser fragmentation in liquid to attain a simple, efficient, ligand-free method for nanoparticle fabrication. By combining simple fabrication processes with a promising device architecture, highly sensitive ZnO nanoparticle/graphene UV photodetectors were successfully demonstrated.

Self-assembled plasmonic metasurfaces are promising optical platforms to achieve accessible flat optics, due to their strong light-matter interaction, nanometer length scale precision, large area, light weight, and high-throughput fabrication. Here, using photothermal continuous wave laser lithography, we show the spectral and spatial tuning of metasurfaces comprised of a monolayer of ligand capped hexagonally packed gold nanospheres. To tune the spectral response of the metasurfaces, we show that by controlling the intensity of a laser focused onto the metasurface that the absorption peak can be reconfigured from the visible to near-infrared wavelength. The irreversible spectral tuning mechanism is attributed to photothermal modification of the surface morphology. Combining self-assembled metasurfaces with laser lithography, we demonstrate an optically thin (λ/42), spectrally selective plasmonic Fresnel zone plate. This work establishes a new pathway for creating flat, large area, frequency selective optical elements using self-assembled plasmonic metasurfaces and laser lithography.

Multiscale laser patterning of indium tin oxide thin films using the combination of direct laser interference patterning (DLIP) and laser induced periodic surface structuring (LIPSS) was studied. By balancing DLIP and LIPSS, structures in an ordered hierarchical pattern consisting of 75 nm LIPSS, 650 nm DLIP, and 50 µm laser spot size were demonstrated. The effects of laser fluence on the DLIP, LIPSS, and grain growth are discussed. The anisotropic conductance due to LIPSS was shown to exceed 50,000:1. Infrared reflectance measurements indicated that the anisotropy was uniform across the laser patterned samples.

Circular arrays offer the ability to form directional beams throughout a full 360 degrees of azimuth coverage without the drawbacks of beam broadening and/or scan loss. These advantages make them an attractive choice for a WiMAX base station antenna where the directional beams in any arbitrary direction facilitate range extension and throughput. In this paper, we demonstrate a 3D-printed circular array that provides a low cost design with simple manufacturing that is suitable for WiMAX base station operation from 5.1 -- 5.8 GHz.

An ultrafast insulator–metal–insulator phase transition cycle in epitaxially strained vanadium dioxide films is observed. The films are characterized by optoelectronic autocorrelation measurements that reveal a 400 fs transient change in response spanning two orders in magnitude. These findings suggest a predominantly electronic mechanism and demonstrate the promise of this material for optoelectronic applications requiring fast, high‐contrast switching.

We report the design, fabrication, and characterization of broadband terahertz emitters based on the semiconductor-metal transition in thin film VO2 (vanadium dioxide). With the appropriate geometry, picosecond electrical pulses are generated by illuminating 120 nm thick VO2 with 280 fs pulses from a femtosecond laser. These ultrafast electrical pulses are used to drive a simple dipole antenna, generating broadband terahertz radiation.