摘要:

Fluorescent microspheres of diameter 10μm embedded in a turbid medium consisting of polystyrene beads suspended in water are imaged under two-photon and single-photon excitation. A comparison of two-photon and single-photon fluorescence images shows that multiple scattering leads to a dominant limiting factor of the signal-to-noise ratio in the former case, while it results in a dominant limiting factor of resolution in the latter case. These results are qualitatively consistent with the predication by the Monte-Carlo simulation based on Mie scattering theory.

ISSN:0950-0340    

DOI:10.1080/09500340008233398

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A method for reducing the reconstruction error and improving the spectral distribution in holographic data storage has been proposed. An optimized phase mask is introduced into the optical system. By using the phase mask, the reconstruction error and uniformity of the spectral distribution can be optimized. The relative importance between reconstruction error and uniformity can be emphasized with an adjustable weight factor. The phase mask can be designed by using amplitude-phase retrieval algorithms. Simulation results have shown the merits of the proposed method. The feasibility of optical realization is investigated briefly.

ISSN:0950-0340    

DOI:10.1080/09500340008233399

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The coupled wave theory (CWT) for axial propagation of light in dielectric thin-film helicoidal bianisotropic media is presented and compared with the full electromagnetic analysis (FEMA). Two sets of formulas are developed for the location and bandwidth of the wavelength regime wherein the circular Bragg phenomenon is exhibited. Multi-layer structures are also analysed using the CWT, the location of the spectral hole in a class of threelayer structures being determined analytically. Absorption and dispersion effects are considered.

ISSN:0950-0340    

DOI:10.1080/09500340008233400

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Although it is well known that light carries momentum and exerts a pressure on objects, a conservation of momentum principle is apparently rarely used in optics. In nonlinear optics light waves interact and may exchange both energy and momentum. We demonstrate that a conservation of momentum principle holds in these cases and in fact its use is widespread but generally unrecognized in the standard mathematical methods. In both the cases of linear basis waves interacting nonlinearly, e.g. coupled-wave theory and frequency mixing, and fully nonlinear waves, we demonstrate that a governing Hamiltonian is related to momentum. Action principles are used to discuss the generality of these results.

ISSN:0950-0340    

DOI:10.1080/09500340008233401

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An experimental investigation of the angular distribution of the light scattered by randomly rough, two-dimensional, isotropic dielectric surfaces is presented. The surfaces, whose profiles constitute good approximations to Gaussian random processes with Gaussian correlation functions, are fabricated in a photoresist and characterized by means of a mechanical profilometer. The substrates employed in the fabrication of the samples consist of thick parallel plates of filter glass that absorb the incident light and whose refractive index is close to that of the photoresist. This allows us to approximate experimentally a situation in which the light is scattered by a randomly rough interface between two semi-infinite dielectric media, illuminated from the air side. The results display features that can be attributed to multiple scattering. In particular, significant amounts of cross-polarized scattered light, as well as an enhanced backscattering peak, were observed in the scattering measurements.

ISSN:0950-0340    

DOI:10.1080/09500340008233402

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this article we study the potential for coherently control spontaneous emission in a four-level scheme. Our control parameter is the relative phase of two laser fields having the same angular frequency. We investigate in detail the trapping conditions, the population dynamics and the behaviour of the (long time) spontaneous emission spectrum, which are now phase dependent. Inhibition of spontaneous emission and extreme spectral narrowing are shown as the relative phase is varied. Our results are interpreted using a dressed state analysis of the dynamics.

ISSN:0950-0340    

DOI:10.1080/09500340008233403

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The usual definition of squeezing, based on the Heisenberg uncertainty principle, measures uncertainty in terms of the standard deviation. It can run into difficulties when applied to squeezing in the two-level atom. An alternative definition of squeezing is presented for this system, based on information entropy theory, which overcomes the disadvantages of the definition based on the Heisenberg uncertainty relation. The utility of this definition is illustrated by examining squeezing in the information entropy of a two-level atom in the Jaynes-Cummings model, and in resonance fluorescence.

ISSN:0950-0340    

DOI:10.1080/09500340008233404

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper we derive the quantum statistical and dynamical properties of nonlinear optical couplers composed of two nonlinear waveguides operating by second subharmonic generation, which are coupled linearly through evanescent waves and nonlinearly through non-degenerate optical parametric interaction. Main attention is paid to generation and transmission of non-classical light, based on a discussion of the squeezing phenomenon, the normalized second-order correlation function and quasiprobability distribution functions. Initially coherent, number and thermal states of optical beams are considered. In particular, results are discussed with dependence on the strength of the nonlinear coupling relatively to the linear coupling. We show that if the Fock state |1⟩ enters the first waveguide and the vacuume state |0⟩ enters the second waveguide, the coupler can serve as a generator of squeezed vacuum state governed by the coupler parameters. Further, if thermal fields enter initially the waveguides the coupler plays a similar role as a microwave Josephson-junction parametric amplifier to generate squeezed thermal light.

ISSN:0950-0340    

DOI:10.1080/09500340008233405

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Photopolymers are studied as holographic recording materials for recording computer-generated phase holograms. The recording was performed using a holographic copying process, in which the master is produced by means of a high resolution graphic device. To our knowledge it is the first time a photopolymer has been used to obtain copies with this technique. As it does not work in real time, it is possible to store the diffractive optical element for a long time because the dye is finished during exposition and no wet processing is needed after exposition. The photopolymer used in these experiments was composed of acrylamide and triethanolamine as the co-initiator, photo-initiated with a dye, yellow eoxine. Components were supported by a film of poly-(vinylalcohol) (PVA). The resulting thickness of the film was 70 & plusmn; 5 μm, symmetrical and asymmetrical diffraction gratings were obtained as phase holograms by index and thickness modulation, monitored with an electron microscope, and the low spatial frequency response of the photopolymer was studied. Diffraction efficiency achieved for copied gratings was about 30%. With this study we get a complete characterization of the photopolymer for the full range of the typical spatial frequencies that can be recorded with the high resolution graphic device used.

ISSN:0950-0340    

DOI:10.1080/09500340008233406

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In surface plasmon resonance (SPR) fibre-optic sensors, the optical power transmittance is important in determining behaviour. In this paper numerical calculations are used to estimate the optical power transmittance of SPR fibre-optic sensors. These analytical estimations can be applied in SPR fibre-optic sensors both with a transducing layer and without a transducing layer. The results of these numerical calculations agree well with previously published experimental results. This work will aid in the design of SPR fibre-optic sensors in terms of geometrical structure, materials and dynamic range as well as allowing the prediction of performance and of limitations of the design.

ISSN:0950-0340    

DOI:10.1080/09500340008233407

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor