ABSTRACT
High quality factor whispering-gallery-mode microresonators are ideally suited for nonlinear optical interactions. We analyze, experimentally and theoretically, a variety of χ((3)) nonlinear interactions in silica microspheres, consisting of third harmonic generation and Raman assisted third order sum-frequency generation in the visible. A tunable, room temperature, cw multicolor emission in silica microspherical whispering-gallery-mode microresonators has been achieved by controlling the cavity mode dispersion and exciting nonequatorial modes for efficient frequency conversion.
Subject(s)
Microspheres , Optics and Photonics/methods , Silicon Dioxide/chemistry , Nonlinear Dynamics , Optics and Photonics/instrumentation , Spectrum Analysis, Raman/instrumentation , Spectrum Analysis, Raman/methodsABSTRACT
Whispering-gallery-mode (WGM) microresonators are used as optical transducers for sensing applications. The typical detection scheme is based on tracking the WGM resonance shift, by scanning with a tunable laser, when a change of the refractive index in the region probed by the WGM takes place. We propose a sensing approach based instead on monitoring the position of the laser line of a fiber ring laser having a WGM microsphere in its loop. We have demonstrated that the induced shift is the same for the ring laser line and for the microsphere resonance. The proposed method requires simpler, cheaper equipment and may also improve the sensor resolution because the ring laser line is much narrower than the microsphere WGM resonance.
ABSTRACT
The Earth's equatorial stratosphere shows oscillations in which the east-west winds reverse direction and the temperatures change cyclically with a period of about two years. This phenomenon, called the quasi-biennial oscillation, also affects the dynamics of the mid- and high-latitude stratosphere and weather in the lower atmosphere. Ground-based observations have suggested that similar temperature oscillations (with a 4-5-yr cycle) occur on Jupiter, but these data suffer from poor vertical resolution and Jupiter's stratospheric wind velocities have not yet been determined. Here we report maps of temperatures and winds with high spatial resolution, obtained from spacecraft measurements of infrared spectra of Jupiter's stratosphere. We find an intense, high-altitude equatorial jet with a speed of approximately 140 m s(-1), whose spatial structure resembles that of a quasi-quadrennial oscillation. Wave activity in the stratosphere also appears analogous to that occurring on Earth. A strong interaction between Jupiter and its plasma environment produces hot spots in its upper atmosphere and stratosphere near its poles, and the temperature maps define the penetration of the hot spots into the stratosphere.
ABSTRACT
Temperatures obtained from early Cassini infrared observations of Titan show a stratopause at an altitude of 310 kilometers (and 186 kelvin at 15 degrees S). Stratospheric temperatures are coldest in the winter northern hemisphere, with zonal winds reaching 160 meters per second. The concentrations of several stratospheric organic compounds are enhanced at mid- and high northern latitudes, and the strong zonal winds may inhibit mixing between these latitudes and the rest of Titan. Above the south pole, temperatures in the stratosphere are 4 to 5 kelvin cooler than at the equator. The stratospheric mole fractions of methane and carbon monoxide are (1.6 +/- 0.5) x 10(-2) and (4.5 +/- 1.5) x 10(-5), respectively.
Subject(s)
Hydrocarbons , Methane , Nitriles , Saturn , Atmosphere , Carbon Monoxide , Extraterrestrial Environment , Spacecraft , Temperature , WindABSTRACT
Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude. If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies. Saturn's south polar stratosphere is warmer than predicted from simple radiative models. The C/H ratio on Saturn is seven times solar, twice Jupiter's. Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers). Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites.
Subject(s)
Saturn , Atmosphere , Carbon , Extraterrestrial Environment , Hydrogen , Methane , Spacecraft , Spectrum Analysis , Temperature , WindABSTRACT
The Composite Infrared Spectrometer observed Jupiter in the thermal infrared during the swing-by of the Cassini spacecraft. Results include the detection of two new stratospheric species, the methyl radical and diacetylene, gaseous species present in the north and south auroral infrared hot spots; determination of the variations with latitude of acetylene and ethane, the latter a tracer of atmospheric motion; observations of unexpected spatial distributions of carbon dioxide and hydrogen cyanide, both considered to be products of comet Shoemaker-Levy 9 impacts; characterization of the morphology of the auroral infrared hot spot acetylene emission; and a new evaluation of the energetics of the northern auroral infrared hot spot.