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2014高考英语作文Quantum dot
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native measure of cavity perfection that does not include propaga-tion effects within the cavity as does the Q factor, of 1.9ǂ106 (ref.26)has been obtained using the mirrors. Optimization of n o and N o ,however, involves joint optimization of the mode volume and fines (or Q ). So, for example, the results cited above ud a resonator with mode volume V=1.69ǂ103µm 3and fines of 4.8×105. A detailed review of the technological limits impod by mirror technology in optimizing Fabry–Perot microcavities for strong-coupling studies has recently been performed 32.
In addition to ultrahigh-fines Fabry–Perot microcavities, the whispering gallery modes of silica and quartz microspheres have received considerable attention 27–29,33,34. Whispering gallery res-onators are typically dielectric spherical structures in which waves are confined by ‘continuous total internal reflection’. Silica micros-pheres, which are robust ultrahigh-Q microresonators, were first studied by Braginsky and Ilchencko 35. Spheres feature an atomic-like mode spectrum in which high ᐉnumber (principal angular index or optical mode) and low radial number modes execute orbits near the sphere’s surface 33(Fig. 5). Excellent surface finish is crucial for maxi-mizing Q , and the formation of spheres through surface tension (that is, as a molten droplet) provides a near atomically
smooth surface (with only a few nanometres or less of surface roughness 28,29). The bulk optical loss from silica is also exceptionally low and record Q fac-tors 28,29of 8ǂ109(and fines 29of 2.3ǂ106) have been obtained. For the measurements, dependence of Q on sphere diameter is consis-tent with Q being limited by loss of surface roughness 29. Also, a time dependency for the measured Q was obrved and is believed to result from water adsorption and formation of OH groups at the sphere’s surface 28,34. For diameters below 20 Ȗm in silica spheres, radiation leakage becomes a significant factor in determining Q 31. The lowest order radial modes (in terms of nodes) with m =ᐉ31are minimal vol-ume, equatorial ring orbits (e Fig. 5) and are best suited for cavity QED. Experimental work has demonstrated strong coupling in this system 34, and recent modelling 31shows that substantial improve-ments in strong coupling are possible using spheres with reduced diameters.
Microcavities bad on photonic crystals (Fig. 3) can provide extremely small mode volumes 7, and donor-mode cavity geometries (in which a small additional hole is drilled within the design of Fig. 3)have been modelled with a neutral atom suspended within the hole 30.Strong coupling is theoretically feasible; however, at prent, Q values in fabricated structures are well below the theoretical optima.
For the purpos of optical probing/output-coupling,Fabry–Perot cavities enable direct ‘endfire’ coupling along the cavity axis. Whispering gallery modes, however, must be pha matched 36
,
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Vacuum Rabi oscillation. An excited atom is introduced into the cavity NATURE|VOL 424|14 AUGUST 2003|/nature841
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vfp是什么Etched
holes
Defect region
Figure 3Cross-ctional illustration of a photonic crystal defect microcavity lar. The
microcavity is formed by dry etching a hexagonal array of holes and subquent lective
etch of an interior region, creating a thin membrane. One hole is left unetched creating a
‘defect’ in the array and therefore a defect mode in the optical spectrum. The mode
(illustrated in green) is confined to the interior of the array by Bragg reflection in the plane手续英语
and conventional waveguiding in the vertical direction. Also, shown in pink are quantum
wells that upon photo pumping provide the amplification necessary for lar oscillation7.
头饰英文Int: Scanning electron micrograph of a photonic crystal defect microcavity lar.
xinxinMicrograph is courtesy of O. Painter and A. Scherer (Caltech, CA).
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怪奇物语百度云843
Mirror surface
Probe lar
Cavity mode
Ultracold
atom
Figure 4If the coupling energy ᐜg in a strongly coupled system exceeds the thermal energy of the atom, then the atomic centre of mass motion will be altered by interaction with the vacuum cavity mode. In recent experiments 21,22, ultracold atoms have been produced to satisfy this condition, resulting in atomic motion that is entrained for substantial periods of time by cavity QED coupling. In this figure, an ultracold atom is entrained in an orbital motion before escaping. Becau the coupling energy depends on the amplitude of the vacuum cavity field near the atom, optical transmission probing of the cavity during the atomic entrainment acts as an ultransitive measure of atomic location. Figure ud with permission of H. J. Kimble (Caltech, CA).
Emission wave
Pump wave
Fibre-taper waveguide
Silica
microsphere
=m mode
Pump wave whispering gallery orbit
Figure 5 Illustration of a silica microsphere whispering gallery resonator. The green orbit is a ᐉ=m mode entrained at the sphere’s surface. Also shown is a fibre taper waveguide ud for power coupling to and from the resonator. In the figure, a blue pump wave induces a circulating intensity within the sphere that is sufficient to induce lar
oscillation (green emission wave). Int: Photomicrograph showing a doped microsphere (the glass
挤压英文sphere contains a rare earth). The green emission in this ca traces the pump wave whispering gallery orbit. The int micrograph was provided by M. Cai.
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