摘要:

Direct access storage devices are widely used in computers to store and manage data. In conventional magnetic recording, a magnetic head flying very close to the disc surface alters the polarization of the magnetic field at the disc surface to write and/or erase information on the disc. An optical disc is a multilayered medium consisting of a thick glass substrate on which many layers of different materials are sputtered. Only one of these layers serves as a recording medium and it is initially magnetized uniformly in one direction. To write on this disc, the initial magnetic field is altered by focusing light from a laser source with high numerical aperture (NA) lens to heat the magnetic medium beyond its Curie point, the temperature at which the magnetic medium loses its magnetization. This domain with zero magnetization is subsequently magnetized in the reversed direction by using an induction magnet. All these processes take place while the disc is rotating at a very high speed with respect to the laser. In this paper, we examine optical imaging and transient heat transfer problems to study the writing process. We first make use of the vector diffraction theory to calculate energy distribution on the disc surface and then use this energy distribution as a source for the heat transfer problem. We examine writing with lenses of various NA and consider various optical effects such as ‘fill factors’ and obscuration, mechanical effects such as the thermal properties of the disc material, and writing conditions. Results pertinent to the design of the disc medium, the optical elements, the mechanical components, and the development of the write algorithm are discussed. We also discuss the quality of the written spots and the resulting data densities during a typical write sequence.

ISSN:0950-0340    

DOI:10.1080/09500349414550111

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Michelson visibility is used to identify areas of correct focusing in stacks of images with progressively severe defocusing. It is found that visibility is a maximum when focusing is correct. An image with partially corrected defocusing is constructed using this criterion.

ISSN:0950-0340    

DOI:10.1080/09500349414550121

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new method for phase unwrapping using a lexicographically updated cellular processor is presented. The method is robust concerning noise induced inconsistencies and those caused by invalid data regions. For a phase map containing small noise, the convergence time of the algorithm is only one iteration. When a large number of inconsistencies are present, the proposed technique may typically take 30 to 60 whole field iterations to converge. The number of iterations required increases with the amount of inconsistencies in the wrapped phase map.

ISSN:0950-0340    

DOI:10.1080/09500349414550131

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new fast algorithm for the computation of the second-order derivatives is described. The method is applicable to the evaluation of the second-order derivatives of reflectance, transmittance and corresponding phase shifts for the light impinging on the substrate from both sides and with respect to any parameters of the system. The time needed for the computation of the whole Hessian matrix is roughly linearly dependent on the number of layers. The precise and fast computation of Hessian matrix enables one to use the optimization methods of quadratic rate of convergence such as modified Newton method and speed up the optimization routines for thin film systems.

ISSN:0950-0340    

DOI:10.1080/09500349414550141

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In optical processors the structure (object or filter) can be considered as a superposition of Fourier components, that is of sinusoidal gratings of different spatial frequencies and orientations. If these gratings do not work in parallel light, aberrations will appear. The fourth-order aberration function introduced by each of the gratings depends on the diffraction or field angle. Taking into account the grating equation and if the wavelength and interference order are fixed, the field angle is associated with the spatial frequency of the grating. When a plane structure with its normal coincident with the optical axis of the lens system is considered, the Seidel aberrations at a given point of the spectral plane are that of a grating which has the spatial frequency that corresponds to that point. The expressions for the aberrations introduced by the structure are totally similar to those obtained for centred optical systems and can be incorporated into the Seidel sums for application to the usual method of predesign.

ISSN:0950-0340    

DOI:10.1080/09500349414550151

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We study the evolution of the wavefunction in the intensity dependent Jaynes—Cummings model. It is shown that apart from the periodic revivals indicated by the dynamics of inversion, half-time revivals of the wavefunction take place in the limit of [nbar] ≫ 1. The decoupled atomic state is a superposition of the upper and lower levels and is independent of the initial atomic condition. The decoupled field state is an even or odd coherent state with a spiked distribution function, depending on the initial atomic state.

ISSN:0950-0340    

DOI:10.1080/09500349414550161

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0950-0340    

DOI:10.1080/09500349414550171

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0950-0340    

DOI:10.1080/09500349414550191

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0950-0340    

DOI:10.1080/09500349414550201

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0950-0340    

DOI:10.1080/09500349414550221

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor