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Contrary to local resonances of single nanostructures, collective (or nonlocal) resonances in periodic metasurfaces, such as surface lattice resonances (SLRs), can significantly enhance light–matter interaction, leading to higher spectral selectivity. The dynamic control of such nonlocal response represents an emerging field of research. While tuning of SLRs has been demonstrated in plasmonic metasurfaces, the use of dielectric metasurfaces provides additional conditions to control both reflectance and transmittance, with minimum absorption effects. A close-to-homogeneous environment is usually required to guarantee the excitation of SLRs. Here, we propose theoretically and demonstrate experimentally a practical strategy for the tuning of SLRs in dielectric metasurfaces when an arbitrary index mismatch is considered between substrate and superstrate. The approach is based on a generalized lattice sum theory that accounts for the presence of a substrate. Dynamic tuning of the SLRs in silicon metasurfaces placed on a substrate is achieved with a changeable superstrate via an optofluidic process. Two tuning mechanisms are revealed corresponding to shifting and damping of the SLR, depending on the superstrate–substrate refractive index contrast. The demonstrated dynamic manipulation of transmission and reflection may be exploited in dielectric metasurfaces for tunable spectral selectivity, sensing, or novel display technologies.

Lanthanides, known as the “vitamin of industry”, have been playing a pivotal role in a wealth of advanced materials and modern technologies including catalysts, magnets, lasers, economical lighting, and solar-energy conversion. With the development of nanoscience, lanthanide nanoparticles have been attracting increasing research interest as a new form of the old materials since 2000. These nanoparticles not only bring properties previously thought impossible in bulk lanthanide materials, but also raise concerns and challenges (e.g. quenching) that were not considered towards practical applications. This dissertation is dedicated to understanding and tackling these challenges with designed colloidal lanthanide nanoparticles. Particularly, the first theme explains how the dopants in the nanoparticle matrix contribute to the size and shape of nanoparticles (doping). The second theme explores the growth behavior of core-shell nanoparticles with controlled interfacial strains (epitaxy). The third theme introduces how to address the quenching challenges and enhance the photoluminescence on nanoparticles with the optimized doping and epitaxy (photon management). We show that the optimized lanthanide nanoparticles have record-high emission efficiency, provide insight for future nanoparticle designs, and can be used as a promising toolset for a wide ranges of research topics including bioimaging, therapeutics, photocatalysis, and optical energy conversion.

Lanthanides, known as the “vitamin of industry”, have been playing a pivotal role in a wealth of advanced materials and modern technologies including catalysts, magnets, lasers, economical lighting, and solar-energy conversion. With the development of nanoscience, lanthanide nanoparticles have been attracting increasing research interest as a new form of the old materials since 2000. These nanoparticles not only bring properties previously thought impossible in bulk lanthanide materials, but also raise concerns and challenges (e.g. quenching) that were not considered towards practical applications. This dissertation is dedicated to understanding and tackling these challenges with designed colloidal lanthanide nanoparticles. Particularly, the first theme explains how the dopants in the nanoparticle matrix contribute to the size and shape of nanoparticles (doping). The second theme explores the growth behavior of core-shell nanoparticles with controlled interfacial strains (epitaxy). The third theme introduces how to address the quenching challenges and enhance the photoluminescence on nanoparticles with the optimized doping and epitaxy (photon management). We show that the optimized lanthanide nanoparticles have record-high emission efficiency, provide insight for future nanoparticle designs, and can be used as a promising toolset for a wide ranges of research topics including bioimaging, therapeutics, photocatalysis, and optical energy conversion.

Theoretical and experimental analysis of active, absorption induced optical tuning of silicon photonic devices using silicon strip waveguides combined with nematic liquid crystal (NLC) claddings. Tuning of the silicon structures is performed under low power photo irradiation, which offers a very simple way to control the spectral response of ring resonator devices., The original document contains color images.

We demonstrate rapid tuning of the emission frequency of a room-temperature mid-infrared quantum cascade laser by external optical pumping. Emission frequency tuning over 0.3 cm(expn -1) (10GHz) has been achieved for a lambda = 9 micro m device by optical generation of electron-hole pairs along the entire length of the laser stripe. Measurements indicate that this approach allows for rapid broadband frequency-modulation of mid-infrared quantum cascade lasers at above 300MHz modulation frequencies., Published in Applied Physics Letters, v102 article ID 011125, 9 Jan 2013. Prepared in cooperation with the Dept of Electrical and Computer Engineering, State Univ of New York at Stony Brook, and the Dept of Electrical and Computer Engineering, The Univ of Texas at Austin.

Crossing a barrier: Molecules with saturated ER2 units (E=C or Si, R=electron-releasing group) inserted between two π-conjugated segments have electronic and optical properties that resemble those of cross-conjugated molecules (see figure). This cross-hyperconjugation provides a deeper understanding of the conjugation phenomenon, and is an alternative to cross-conjugation in the design of molecules for nano and materials applications.

We use an elastomer as infill material for a photonic crystal. As a result of the thermal-expansion-induced strongly negative thermal optical coefficient, this material is highly suitable for thermal tuning of the transmission of a cavity. This is demonstrated by global infilling of a hole-type silicon photonic crystal slab and global thermal tuning. In the temperature range 20-60?°C the cavity peak shows a pronounced elastomer-induced blue shift of 2.7 nm, which amply overcompensates the red shift arising from the thermo-optic property of the silicon. These results qualify the elastomer for tuning by local optical heating., QN/Quantum Nanoscience, Applied Sciences

A nonlinear photonic crystal with a rectangular domain lattice of 6.09x6 mu m(2) has been fabricated and characterized in flux-grown KTiOPO4. It was used to demonstrate continuous-wave and multiple beam tunable blue second harmonic generation., QC 20100525

Mode-dependent shifts of resonant frequencies of cavities in liquid crystal (LC) infiltrated planar photonic crystals (PhC) are experimentally observed when the temperature is varied across the LC ordering transition. The shifts can be in opposite directions, even for two very similar nearly degenerate modes. The behavior is attributed to the different interactions of the modes with the two components of the refractive index of the LC infill and directly demonstrates that at least a substantial amount of the LC is oriented perpendicular to the PhC-hole axis., Kavli Institute of Nanoscience, Applied Sciences

Mode-dependent shifts of resonant frequencies of cavities in liquid crystal (LC) infiltrated planar photonic crystals (PhC) are experimentally observed when the temperature is varied across the LC ordering transition. The shifts can be in opposite directions, even for two very similar nearly degenerate modes. The behavior is attributed to the different interactions of the modes with the two components of the refractive index of the LC infill and directly demonstrates that at least a substantial amount of the LC is oriented perpendicular to the PhC-hole axis., Kavli Institute of Nanoscience, Applied Sciences