Harnessing the Natural Resonances of Time-Varying Dispersive Interfaces.

Space-time modulation of electromagnetic parameters offers novel exciting possibilities for advanced field manipulations. In this study, we explore wave scattering from a time-varying interface characterized by a Lorentz-type dispersion with a steplike temporal variation in its parameters. Our findings reveal a new process: an unconventional frequency generation at the natural resonances of the system.

All-optical tunable wavelength conversion in opaque nonlinear nanostructures.

We demonstrate a simple, femtosecond-scale wavelength tunable, subwavelength-thick nanostructure that performs efficient wavelength conversion from the infrared to the ultraviolet. The output wavelength can be tuned by varying the input power of the infrared pump beam and/or relative delay of the control beam with respect to the pump beam, and does not require any external realignment of the system. The nanostructure is made of chalcogenide glass that possesses strong Kerr nonlinearity and high linear refractive index, leading to strong field enhancement at Mie resonances.

Near-infrared to ultra-violet frequency conversion in chalcogenide metasurfaces.

Chalcogenide photonics offers unique solutions for a broad range of applications from mid-infrared sensing to integrated, ultrafast, ultrahigh-bandwidth signal processing. However, to date its usage has been limited to the infrared part of the electromagnetic spectrum, thus avoiding ultraviolet and visible ranges due to absorption of chalcogenide glasses. Here, we experimentally demonstrate and report near-infrared to ultraviolet frequency conversion in an AsS-based metasurface, enabled by a phase locking mechanism between the pump and the inhomogeneous portion of the third harmonic signal.

Universal Multienergy Harvester Architecture.

The energy available in the ambient vibrations, magnetic fields, and sunlight can be simultaneously or independently harvested using universal architecture. The universal harvester design is shown to effectively convert ambient magnetic fields, vibration, and light into electricity. The architecture is composed of a perovskite solar cell integrated onto a magnetoelectric composite cantilever beam.

Effects of flow recirculation on acoustic and dynamic measurements of rotary-wing systems operating in closed anechoic chambers.

An experimental campaign was undertaken to identify the effects posed by flow recirculation on the dynamic performance and acoustic emissions of an isolated rotor, operating in hover in a sealed anechoic chamber. It is shown that flow recirculation is an artifact of testing rotary-wing systems in an enclosed environment, and results in a significant amplification of tonal and broadband noise components. The acoustic emissions produced while the recirculated flow is ingested into the rotor disk vary from those emitted by similar rotors operating in clean inflow conditions.

Widely tunable compact terahertz gas lasers.

The terahertz region of the electromagnetic spectrum has been the least utilized owing to inadequacies of available sources. We introduce a compact, widely frequency-tunable, extremely bright source of terahertz radiation: a gas-phase molecular laser based on rotational population inversions optically pumped by a quantum cascade laser. By identifying the essential parameters that determine the suitability of a molecule for a terahertz laser, almost any rotational transition of almost any molecular gas can be made to lase.

Laser-sculptured ultrathin transition metal carbide layers for energy storage and energy harvesting applications.

Ultrathin transition metal carbides with high capacity, high surface area, and high conductivity are a promising family of materials for applications from energy storage to catalysis. However, large-scale, cost-effective, and precursor-free methods to prepare ultrathin carbides are lacking. Here, we demonstrate a direct pattern method to manufacture ultrathin carbides (MoC, WC, and CoC) on versatile substrates using a CO laser.

Quantitative analysis of gas phase molecular constituents using frequency-modulated rotational spectroscopy.

Rotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial reconstruction of integrated line strengths from modulated spectra, the correlation of pressure-dependent line shape and strength with partial pressure, and the multiple standing wave interferences and modulation-induced line shape asymmetries that sensitively depend on source-chamber-detector alignment. Here, we introduce a quantitative analysis methodology that overcomes these challenges, reproducibly and accurately recovering gas molecule concentrations using a calibration procedure with a reference gas and a conversion based on calculated line strengths.

Ultra-high performance wearable thermoelectric coolers with less materials.

Thermoelectric coolers are attracting significant attention for replacing age-old cooling and refrigeration devices. Localized cooling by wearable thermoelectric coolers will decrease the usage of traditional systems, thereby reducing global warming and providing savings on energy costs. Since human skin as well as ambient air is a poor conductor of heat, wearable thermoelectric coolers operate under huge thermally resistive environment.