We detect macroscopic currents driven by intense light fields in a photoconductive antenna, which we switch on using ultrafast vacuum ultraviolet light pulses. By comparing these currents with the vector potential of the incident light, we can follow nonequilibrium inter- and intra-band carrier dynamics with attosecond resolution.
Phase singularities are loci of darkness surrounded by light in a scalar field. We engineer an array of closely-spaced identical point singularities structured along the optic axis. The array is experimentally realized with a TiO2 metasurface under 760 nm narrowband illumination. We study possible application in blue-detuned neutral atom trap arrays, for which this field would enforce 3D confinement and a potential depth around 0.22 mK per watt of trapping power. The field is tolerant to around 10 nm changes in wavelength with a 0.11 degree angular bandwidth. Metasurface-enabled point singularity engineering may simplify and miniaturize the architecture required for super-resolution microscopes and dark traps.
Faraday rotation is a physical phenomenon that results in the rotation of linearly polarized light when it passes through a magneto-optical (MO) material. The angle of rotation is linearly proportional to the product of an applied magnetic field and the distance light travels inside the material. The proportionality constant is called the Verdet constant. EuS is a semiconductor material that poses a very large Verdet constant at low temperatures (~6K) Its room temperature properties have not been studied so far. In this work, we measured a Verdet constant of EuS at room temperature.
Since the emergence of nanoscale photonic systems to tailor light at-will, electro-optic transducers have become critical components to link the optical domain further with the electronic domain. Many electro-optic transducers have been reported for integrated photonic circuits that are ideally suited for fiber-based applications. Instead, free-space electro-optic transducers could target entirely different applications that require a combined in-plane and time-domain control of freely propagating light at high speeds. Here, we demonstrate nano-engineered free-space electro-optic transducers that combine low-loss dielectric Mie resonators arranged into a meta-array and high-performance electro-optic molecules. We discuss how various design parameters influence the tuning of optical resonances which we show to reach up to 20 nm at a center wavelength of 1550 nm.
Optical singularities are dark regions of a light field that exhibit rich and nonintuitive behaviors such as local wavenumbers that far exceed the light field wavenumber. For example, helical beams have a one dimensional singularity along the axis of the optical vortex where the phase is undetermined. We demonstrate that both phase and polarization singularities can be engineered and that in addition to the common one-dimensional string-like topologies, we can produce a broader family of 0D (point) and 2D (sheet) singularities. As a potential application, we design an array of point singularities to serve as identical blue-detuned cold atom traps with three-dimensional confinement. Singularity engineering imbues microscale wavefront engineering tools with the ability to produce exotic forms of light deterministically and on-demand and has wide applicability to other wave-like systems in physics.
We demonstrate an electrically tunable metasurface from an array of nanoresonators coated by a single layer of electro-optic molecules that are embedded in a polymer matrix. By periodic poling of the non-linear coating in plane, we tune the resonant frequency of the array under an applied bias at high speeds and over a broad range in the near-infrared.
All-dielectric focusing metasurfaces have attracted a lot of attention in recent years because of their lightweight, superior performance, and compact form factor. Traditionally, metasurfaces are fabricated from dielectric material shaped into pillar-like structures. Pillars are fragile and tend to fall, especially for high aspect ratio structures. We have developed and characterized a monolithic metasurface in the infrared spectral range. The monolithic design of realized metasurfaces allows for the creation of rugged structures that can withstand harsh cleaning and handling, while maintaining good focusing performance. This metasurface platform thus widens the range of practical applications for metalenses.
Energy efficient generation of white light has become an important issue in recent years. Technology of white-light emitting diodes (LEDs) is one of the promising directions. The main challenges in the LED production are understanding scattering, absorption and emission from ab-initio, and obtain chromaticity independent emission directions. Physical understanding of multiple light scattering in the LED can provide us with simple tools for extracting optical parameters of this system.
We have studied the transport of light through phosphor diffuser plates that are used in commercial solid-state lighting modules (Fortimo). These polymer plates contain YAG:Ce+3 phosphor particles that both elastically scatter light and Stokes shift light in the visible wavelength range (400-700 nm). We excite the phosphor with a narrowband light source, and measure spectra of the outgoing light. The Stokes shifted light is spectrally separated from the elastically scattered light in the measured spectra. Using this technique we isolate the elastic transmission of the plates. This result allows us to extract the transport mean free path ltr over the full wavelength range by employing diffusion theory. Simultaneously, we determine the absorption mean free path labs in the wavelength range 400 to 530 nm where YAG:Ce+3 absorbs. The diffuse absorption (µ_a=1/l_abs ) spectrum is qualitative similar to the absorption coefficient of YAG:Ce+3 in powder, with the diffuse spectrum being wider than the absorption coefficient. We propose a design rule for the solid-state lighting diffuser plates.
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