Electromechanical tuning of double-membrane Photonic Crystal Cavities
PL spectra and peak shift obtained by applying a gradually increasing voltage are shown in Fig. 1b. We report up to 7 nm mode shift when the applied bias reaches 8.6 V. By further increasing the voltage we observe the well-known pull-in phenomenon: the cantilever collapses on the substrate because electrostatic forces win over elastic forces. We attribute the need for high voltages to fabrication issues and imperfections such as the complete erosion of the p-doped InGaAsP layer in the photonic crystal region during the sacrificial layer etching. Further process optimization should result in PCCs with Q factors>10'000, electromechanically tunable over >30 nm.
Optomechanical wavelength and energy conversion in high- double-layer cavities of photonic crystal slabs.
We demonstrate that ultrasmall double-layer photonic-crystal-slab cavities exhibit a very high-Q value for a wide range of the layer spacing, which enables us to realize unique optomechanical coupling. By mechanically varying the separation, we can achieve extraordinarily large wavelength conversion. In addition, the light stored in the cavity can generate a large radiation force. We show that this system exhibits extremely high energy conversion efficiency between optical and mechanical energy, leading to a novel approach for the optomechanical control of light and matter.
The fragmentation of small asteroids in the atmosphere
The fragmentation of a small asteroid in the atmosphere greatly increases its cross-sections for aerodynamic braking and energy dissipation. The differential pressure across a meteoroid disperses its fragments at a velocity that increases with atmospheric density and impact velocity and decreases with meteoroid density. At a typical impact velocity of 22 km/s, the atmosphere absorbs more than half the kinetic energy of stony meteoroids with diameters, D M < 220 M AND IRON METEOROIDS WITH D M < 80 m. The corresponding diameter for comets with impact velocity 50 km/s is D M < 1600 m. Most of this energy dissipation occurs in a fraction of a scale height, which causes large meteoroids to appear to »explode« or »flare« at the end of their visible paths