摘要:

We propose an experiment that is a variation of the Schrödinger's cat ′paradox' wherein the entanglement between a microscopic system and a macroscopic system is of primary interest. The experiment involves tunable entanglement and serves as a model for controllable decoherence in the context of cavity quantum electrodynamics where atoms interact dispersively with a cavity field initially in a coherent state. The interaction produces an entanglement between the atom and the field, and the degree of entanglement can be probed by subjecting the atom to resonant classical radiation after it leaves the cavity. The amplitude of the resulting Rabi oscillations reflects the degree of the entanglement, there being no Rabi oscillations when the entanglement is maximum. We show that the cavity damping does not affect the experiment.

ISSN:0950-0340    

DOI:10.1080/09500349908230398

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We calculate the nonlinear phase shift acquired by a laser beam in propagating through a one-dimensional photonic bandgap material, that is a material in which the linear refractive index is periodically modulated along the direction of propagation. We find that the nonlinear phase shift shows resonances for laser frequencies close to the edge of the stop band of the photonic bandgap structure. Enhancements of the nonlinear phase shift compared with that of a homogeneous nonlinear optical material by a factor of approximately five are predicted under realistic laboratory conditions. We find that similar enhancements of the two-photon absorption rate can occur for a material with an imaginary nonlinear susceptibility. We also treat the case of a photonic bandgap material containing a ′defect,' that is a central region somewhat too thick to conform to the periodicity of the system, and find that the nonlinear phase shift can be enhanced by a factor of approximately thirty.

ISSN:0950-0340    

DOI:10.1080/09500349908230399

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A diffractive optical element (DOE) has been designed, fabricated and used in an external feedback configuration to set the wavelength of operation of uncoated Fabry-Pérot diode lasers. The DOE was designed to replace the conventional elements of an external feedback system, which are a collimating lens and grating in the Littrow configuration. The goal was to simplify use of the external cavity laser by replacing the lens and grating with a single optical element while maintaining the performance that is achieved with a grating and lens. Four DOEs were fabricated with two different focal lengths and two different reflectivities. DOE external cavity lasers were tested for maximum tunable range and stability of the wavelength of operation and compared with an external cavity laser based on a lens and grating in the Littrow configuration. A 40 nm tuning range was achieved with the DOE external cavity laser and this is comparable with the tuning range of the external cavity lasers based on a grating and collimating lens in the Littrow configuration.

ISSN:0950-0340    

DOI:10.1080/09500349908230400

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Applications such as refractive surgery demand an objective appraisal of the retinal image quality. The modulation transfer function (MTF) provides that information when measured directly. Moreover, the MTF obtained using a simple and objective method such as that described in this paper allows the neural contrast sensitivity function (CSF) to be obtained from the global CSF and the MTF. When calculating the MTF it must be borne in mind whether the applicable theory is coherent or incoherent. In the literature, the developed theory presents some approximations and incongruities. Also, it is interesting to note that the method of recording the MTF (short or long time of integration, sum of images, etc.) and the source used (laser or others) can essentially change the nature of the problem. This theory is not directly applicable to any experiment. This work comprises a thorough theoretical study of the possible cases according to the experimental method and therefore as a function of the coherence degree. Two different solutions are found: the MTF calculated as the square root of the Fourier Transform (FT) of the recorded intensity for any light source or the MTF calculated as the FT square root of the image.

ISSN:0950-0340    

DOI:10.1080/09500349908230401

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A new aqueous photopolymer containing the monomers acrylamide,N,N'-methylenbisacrylamide and zinc acrylate, the initiators 4,5-diiodosuccinylfluorescein (2ISF) and methylene blue (MB), and the coinitiator sodiump-toluenesulphinate is described. This formulation exhibits a clear enhancement of the high-energy sensitivity upon irradiation with 514 or 633 nm light (Ar+laser or He–Ne laser respectively), with respect to the same mixture but with only one of the two dyes, reaching maximum diffraction efficiencies of 15–20% with 15–60 mJ cm−2. This enhancement is explained by the more efficient photogeneration of initiator radicals by the ground-state formation of an ion-pair complex between cationic (MB) and anionic (2ISF) chromophores. This must compensate the observed decrease in the absorbance of the mixture of the two dyes at 514 nm, with respect to the absorbance of the same medium but with only 2ISF (maximum absorption at 490 nm). A clear absorbance increase at 633 nm, with respect to the absorbance of this system with only MB (maximum absorption at 660 nm), must also favour photopolymerization.

ISSN:0950-0340    

DOI:10.1080/09500349908230402

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this work we present grating-coupled surface plasmon characterization of aluminium in the ultraviolet. Light of wavelength 325 nm from a helium-cadmium laser was used to excite surface plasmon-polaritons both at a buried aluminium-silica interface and on oxidized aluminium. By fitting the angle-dependent reflectivity data to model grating theory, the optical permittivity of uncontaminated aluminium at 325 nm is deduced. These results are compared with those extrapolated from prism-coupled surface plasmon excitation in the visible. The further characterization of the oxidized aluminium allows optical non-contact profilometry to be performed on short-pitch gratings that are opaque or are comprised of materials with ill-defined optical properties. This profile characterization is demonstrated for a short-pitch grating manufactured in photoresist.

ISSN:0950-0340    

DOI:10.1080/09500349908230403

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The theory of quantum-optical measurements is developed via a Heisenberg picture approach to quantum scattering theory. The multitime quantum correlation functions describing the measurements are expressed in terms of input or output operators, which are related via the scattering operator.

ISSN:0950-0340    

DOI:10.1080/09500349908230404

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Optical sensors are designed usually for microscopic or for macroscopic applications. White-light interferometry on the other hand enables high-resolution measurements to be made for small and for large fields. In this paper we present a flexible set-up that can be used for both microscopic and macroscopic applications. The magnification can easily be changed in seconds and the zoom range is greater than 160. This set-up is especially designed for the investigation of optically rough surfaces. A novel filtering technique enables fast and accurate data acquisition and evaluation with standard hardware components. Further we demonstrate results of roughness measurements in different scales.

ISSN:0950-0340    

DOI:10.1080/09500349908230405

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A detailed near-field analysis of planar waveguides supporting two modes has been carried out. Theoretical calculations for both step- and gradedindex profiles, have shown the near-field features produced by interference of the two mode wavefunctions, which depend on their phase difference and intensity ratio. Theoretical results have been experimentally confirmed by performing an independent control of the two last magnitudes during the measurements. Fitting the calculated near-field intensity distribution to the measured one, the index profile of the waveguide has been reconstructed. The profile parameters differ by less than 5% from those obtained with them-line method. Theoretical and experimental single mode analysis, also included for comparison, result in less accurate parameters showing index jump deviations, with respect to them-line method, of the order of 10%.

ISSN:0950-0340    

DOI:10.1080/09500349908230406

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The LiF:F+2colour centre laser was achieved by creating the F+2centres through the photoionization of the F2colour centres at room temperature using 532 nm laser radiation and simultaneously by exciting the produced F+2centres with the same 532 nm radiation. Simultaneous laser oscillation due to the F2and F+2colour centres was observed but the F2laser oscillation disappeared in about 100s during the pumping. It was observed that the F+2laser intensity increases with a form given byP(F+2) ∼P2, wherePis the pump pulse energy, but it increases with a form given byP(F+2) ∼P0.85atP> 8 mJ. A discussion on the reason for this deviation from theP2law is given.

ISSN:0950-0340    

DOI:10.1080/09500349908230407

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor