Tunneling induced quantum interference experienced by an incident probe in asymmetric double quantum wells can easily be modulated by means of an external control light beam. This phenomenon, which is here examined within the dressed-state picture, can be exploited to devise a novel all-optical ultrafast switch. For a suitably designed semiconductor heterostructure, the switch is found to exhibit frequency bandwidths of the order of 0.1 THz and response and recovery times of about 1 ps. DOI: 10.1103/PhysRevLett.95.057401 PACS numbers: 78.67.De, 42.50.Gy, 42.50.Hz, 78.66.Fd Transmission and switching of data using all-optical devices is currently the ultimate goal of most telecommunication research. To build all-optical networking systems, optical analogues of existing microelectronics devices must clearly be found. Interesting proposals toward the realization of fast switches, for instance, have already been brought forward whereas important steps toward their actual implementation are now being made. Schemes based on dipole-dipole interactions [1], nonlinear Bragg diffraction [2], photonic band-gap materials [3], as well as those most recent ones based on quantum interference in atomic media [4 -7] all seem to be quite promising.This Letter describes a proof-of-principle study demonstrating that tunable tunneling induced quantum interference in asymmetric quantum wells can be exploited to devise an efficient new mechanism for ultrafast and broadband all-optical switching working at low temperatures (T 10 K). Unlike most familiar switching schemes based on photo-induced changes of the medium macroscopic refractive index [3] or other less usual ones based instead on virtual excitation of spin-polarized excitons [8] or on switchable mirrors made of thin polycrystalline films [9], this mechanism relies on quantum interference and hence it is quite sensitive. Quantum interference based phenomena such as, e.g., coherent population trapping [10], electromagnetically induced transparency [11], lasing without inversion [12], and light speed reduction [13] have recently attracted considerable attention. For many potential applications, solid-state solutions to implement these effects, first predicted and observed in dilute atomic media, are preferred and are now being sought after. In solid media [14] only few proposals followed the original idea of making use of quantum interference to devise an optical switch, first suggested [4] to work and recently observed [6] on a four-level atomic system.We investigate the steady-state and transient behavior of a weak probe light signal incident upon an asymmetric quantum well. The probe can be stopped in the presence of an external control switch beam but made instead to propagate with little absorption when the switch beam is off. The different response depends, respectively, on whether tunneling induced quantum interference is quenched or well developed. Such a control of quantum interference hinges on the creation of a new dipole allowed intersubband transition. Large pro...

An intense laser-induced fluorescence of sodium and of other alkali atoms (K, Rb) at room and lower temperatures has been observed in polysiloxanecoated cells, producing a vapor density of the metal which is much higher than that corresponding to the thermal equilibrium between the vapor and the condensed phase. This enhancement is attributed to the light-induced ejection of atoms absorbed by the polysiloxane coating. The atomic density of the vapor can be manipulated by changing either the laser power or frequency. The dependence of the atomic density on these and other parameters as well as its time-dependent behavior are studied experimentally. A tentative interpretation of the phenomenon is discussed in terms of the properties of solutions of the alkali metals in several solvents.PACS 32.80 -Photon interactions with atoms. PACS 32.80.Fb -Photoionization and photodetachment.

The photoejection of Na and Na 2 from surfaces prepared by adsorption of sodium vapor on solid films of polydimethylsiloxane ͑PDMS͒ of various molecular weights and structures is found to be dependent on light intensity and frequency. At low power levels the desorption yields of Na and Na 2 are linear functions of desorbing light power and exhibit frequency thresholds for photoejection analogous to the photoelectric effect. The frequency thresholds are 9500 cm Ϫ1 for Na and 11 500 cm Ϫ1 for Na 2 , and the 2000-cm Ϫ1 difference can be accounted for with a model in which the alkali-metal species form charge-transfer complexes Na ϩ PDMS Ϫ and Na 2 ϩ PDMS Ϫ , with the cations stabilized by interaction with the oxygen atoms of the PDMS polymer backbone. The ejection mechanism takes place by a reverse charge transfer to form a less polar complex with enough energy to eject Na or Na 2 from the surface.

Triplicate groups of 40 Japanese seabass Lateolabrax japonicus (initial weight, 11.3 ± 0.4 g) reared in seawater (salinity, 30.0-33.0 g L -1 ) were fed with five isonitrogenous (41.3 ± 0.2% crude protein) and isoenergetic (18.5 ± 0.3 MJ kg -1 ) experimental diets formulated with increasing lipid levels (4.3, 8.4, 12.2, 15.8 and 20.1% lipid) for 10 weeks. Survival throughout the feeding experiment ranged from 87.5 to 100%, but the survival of fingerlings fed with the 4.3% lipid diet was significantly lower than the rest of the diets. At the end of the feeding experiment, fish fed with 12.2% lipid diet showed optimal growth performance (P \ 0.05). Lipid contents of whole body, liver and muscle increased in parallel with the increase in dietary lipid levels. Viscerosomatic index (VSI), hepatosomatic index (HSI) and muscle lipid content were higher in 20.1% lipid group than those in the rest of the lipid level groups indicating that viscera and muscle tissues played important contributions to body lipid deposition. High proportions of 18:1n-9, eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), and low concentrations of n-6 polyunsaturated fatty acids (PUFAs) occurring in liver and muscle, to some extent, reflected fatty acid (FAs) composition in the experimental diets.

We report on the transition from the strong to the weak light-matter coupling regime between an intersubband excitation and a photonic crystal resonance in a nanostructured semiconductor membrane. Such a transition is induced by varying the intensity of an ultrafast light pulse, which is employed for pumping and probing the system eigenmodes. The phenomenon is interpreted in terms of the saturation of the intersubband transition due to the large number of photoexcited electrons in the quantum well, as confirmed by a thorough analysis performed both in frequency and time domain