125 research outputs found
In-bulk and surface structuring of sapphire by femtosecond pulses
No full textThe actual space–time dependent intensity distribution of a tightly focused (numerical aperture NA = 1.35) Gaussian femtosecond pulse is modeled inside dielectric material. Such focusing is typically used for recording with sub-wavelength resolution inside dielectrics. The multi-pulse structuring inside the bulk and on the surface of sapphire are demonstrated. Formation of nano-cracks and nano-crystals is revealed inside the crystalline sapphire. Ripple formation on the surface is discussed in terms of the efficacy map calculated by theory given in ref. [J.E. Sipe, J.F. Young, J.S. Preston, H.M. van Driel, Laser-induced periodic surface structure. I. Theory, Phys. Rev. B 27 (2) (1983) 1141–1154.]
Decoherence of highly mixed macroscopic quantum superpositions
No full textIt is known that a macroscopic quantum superposition (MQS), when it is exposed to an environment, decoheres at a rate scaling with the separation of its component states in phase space. This is more or less consistent with the well-known proposition that a more macroscopic quantum state is reduced more quickly to a classical state in general. Effects of initial mixedness, however, on the subsequent decoherence of MQSs have been less known. We study the evolution of a highly mixed MQS interacting with an environment and compare it with that of a pure MQS having the same size as the central distance between its component states. Although the decoherence develops more rapidly for the mixed MQS in short times, its rate can be significantly suppressed after a certain time and becomes smaller than the decoherence rate of its corresponding pure MQS. In an optics experiment to generate a MQS, our result has the practical implication that nonclassicality of a MQS can still be observable in moderate times, even though a large amount of noise is added to the initial state
Strong control and squeezing effects of radiation states in a slab waveguide sandwiched between two omnidirectional mirrors
No full textThe effect of sandwiching a slab waveguide in air between two omnidirectional mirrors on the local density of modes is investigated theoretically. Design aspects of such a structure are considered, and it is shown that the local density of modes other than the slab-guided mode can be strongly controlled by the mirrors. Lowering of this quantity may lead to a strong suppression of loss of the slab-guided mode owing to excitation of radiation modes by impurity scattering or by transitions in the slab. Presented time-domain calculations indicate that by small time-dependent structural changes light, radiated by an atom or scattered by an impurity, can be squeezed back into its original state
Design, fabrication, and characterization of deep-etched waveguide gratings
No full textOne-dimensional (1-D) deep-etched gratings on a specially grown AlGaAs wafer were designed and fabricated. The gratings were fabricated using state-of-the-art electron beam lithography and high-aspect-ratio reactive ion etching (RIE) in order to achieve the required narrow deep air slots with good accuracy and reproducibility. Since remarkable etch depths (up to 1.5 /spl mu/m), which completely cut through the waveguide core layer, have been attained, gratings composed of only five periods (and, thus, shorter than 6 /spl mu/m) have a bandgap larger than 100 nm. A defect was introduced by increasing the width of the central semiconductor tooth to create microcavities that exhibit a narrow transmission peak (less than 7 nm) around the wavelength of 1530 nm. The transmission spectra between 1460 and 1580 nm have been systematically measured, and the losses have been estimated for a set of gratings, both with and without a defect, for different periods and air slot dimensions. Numerical results obtained via a bidirectional beam propagation code allowed the evaluation of transmissivity, reflectivity, and diffraction losses. By comparing experimental results with the authors' numerical findings, a clear picture of the role of the grating's geometric parameters in determining its spectral features and diffractive losses is illustrated
Historische en hedendaagse systeem-innovaties in de glastuinbouw en varkenshouderij: Een innovatie-sociologische analyse
No full textTransities en systeem-innovaties in de landbouw zijn het thema van dit rapport. Klimaatverandering, energiegebruik, methaan-emissies, dierenwelzijn, economische concurrentie, voedselschandalen (BSE, dioxine), verzuring, stankproblemen, landschapsinrichting, en rurale ontwikkeling zijn enkele van de socio-economische ontwikkelingen die druk creëren op het landbouwsysteem. Veel van deze ontwikkelingen kunnen (waarschijnlijk) niet binnen de grenzen van het bestaande systeem het hoofd geboden worden. Daarom is het thema van transities naar nieuwe systemen (systeem-innovatie) gestegen op de maatschappelijke en politieke agenda. Wat betreft empirische focus gaat dit rapport over transities in twee sectoren: glastuinbouw en varkenshouderij. Voor beide sectoren is een studie gedaan van historische transities en een studie van contemporaine transities ‘in the making’. Hedentendaage, staat de glastuinbouw onder druk wegens hoog energiegebruik (en dus CO2 emissies en klimaatverandering), vooral gerelateerd aan ruimteverwarming met gas. De varkenssector staat onder druk wat betreft dierenwelzijn (o.a. ruimtegebruik in stallen, onverdoofd castreren van biggetjes), internationale economische concurrentie, en mestproblematiek (verzuring, stank). In reactie op deze druk, zijn in beide sectoren radicale innovatietrajecten gestart die systeemcomponenten aanzienlijk veranderen
In-bulk and surface structuring of sapphire by femtosecond pulses
No full textThe actual space-time dependent intensity distribution of a tightly focused (numerical aperture NA = 1.35) Gaussian femtosecond pulse is modeled inside dielectric material. Such focusing is typically used for recording with sub-wavelength resolution inside dielectrics. The multi-pulse structuring inside the bulk and on the surface of sapphire are demonstrated. Formation of nano-cracks and nano-crystals is revealed inside the crystalline sapphire. Ripple formation on the surface is discussed in terms of the efficacy map calculated by theory given in ref. [J.E. Sipe, J.F. Young, J.S. Preston, H.M. van Driel, Laser-induced periodic surface structure. I. Theory, Phys. Rev. B 27 (2) (1983) 1141-1154.]
Injecting and controlling spin populations and currents in semiconductors using optically induced quantum interference effects
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