摘要:

Average solid angles subtended by an external contour of a given body from several points are required for the calculation of radiation fluxes or particle beams that are incident on the body from multiple-point isotropic emitters of analogous kinds. To consider the refraction effects for fluxes of light propagating through various optical media, knowledge of the angular distributions of such average solid angles is necessary. In this paper the formula describing angular dependence of the average solid angle subtended by a circular disc from uniformly distributed points within the circular surface of a parallel and coaxial disc was derived analytically and used for the calculation of some representative results. The solution has been made in the cylindrical coordinate system. The final and some intermediate formulas were expressed as functions of the polar angle, of the radii of both discs and of the distance between their planes. These formulae were represented by superpositions of simple elementary functions, single integrals of, these superpositions and by incomplete and complete Legendre—Jacobi elliptic integrals of all three kinds. Mathematica 2.2.3 software was used to illustrate graphically the relationships between some computed data. These data indicate that the derived formula is directly applicable in any computer programs calculating the Legrendre—Jacobi elliptic integrals to estimate the fluxes of optical radiation and particle beams propagated within a non-absorbing homogeneous medium. The expressions obtained may also be used to calculate the fluxes of optical radiation propagated through various homogeneous media.

ISSN:0950-0340    

DOI:10.1080/09500340008235090

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An experimental investigation of a pulsed tunable injection-seeding system pumped by a Nd:YAG laser is presented. The slave laser (SL) of the system is a gain-switched Ti:Sapphire laser with a dual-channel competitive cavity which consists of a main ring channel and an auxiliary linear one with different lengths. The use of this configuration results in full and reliable suppression of both the perturbing reverse radiation from the SL to the master laser (ML) and the broadband spectral background of the SL's ring channel. This is achieved irrespective of the ratio between the energies of the SL and ML, fluctuations of laser parameters, and spectral detuning. We take advantage of the gain-switched regime of the Ti:Sapphire laser to avoid simultaneous competition between the SL's channels; this allows us to obtain spectrally pure, unidirectional output radiation with high seeding and overall efficiency. The principle of operation of the ring-linear-cavity Ti:Sapphire slave laser provides a natural optical isolation between the SL and ML; this makes such lasers suitable for use as regenerative amplifiers when seeded by single-frequency diode lasers as well as in chirped-pulse-amplification systems to amplify ultrashort laser pulses without the necessity of optical isolators.

ISSN:0950-0340    

DOI:10.1080/09500340008235091

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper describes finite-element techniques to simulate scattering of electromagnetic radiation from objects in inhomogeneous solution spaces. The motivation for the work is the development of software to model field interactions at surfaces for scanning near-field optical microscopes. The calculation is performed in a computational anechoic chamber—a finite volume surrounded by an absorbing layer to simulate free space. The volume may consist of any configuration of materials, including lossy dielectrics and ferrites. The first step in the procedure is to find a distribution of element current sources consistent with the absorbing boundaries that generate the desired unperturbed wave solution. The base solution is not limited to simple plane waves. It may consist of any valid electromagnetic disturbance including mixed propagating and evanescent waves. The second step is to introduce one or more scattering objects and to solve finite-element equations for the perturbed fields. One advantage of the approach is that the boundaries need only absorb the scattered field components. Another useful feature for the microscopy calculations is that the method is equally effective for near and far fields. In simulations of small object scattering the absorbing boundary can be at a distance much less than a wavelength.

ISSN:0950-0340    

DOI:10.1080/09500340008235092

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The theory of interaction between an arbitrary electromagnetic shaped beam and a sphere with an eccentrically located spherical inclusion is presented. This theory is built as a synthesis between two available theories (i) the generalized Lorenz-Mie theory for a homogeneous sphere (illuminated by an arbitrary shaped beam) and (ii) the theory of interaction between a plane wave and an eccentrically stratified dielectric sphere.

ISSN:0950-0340    

DOI:10.1080/09500340008235093

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A new technique for determining the stress of thin films is described. This technique combines digital phase shifting interferometry with image-processing software. A circular disc polished on one side is used as the coated substrate during film deposition. The average stress in thin films can be derived by comparing the deflection of the substrate before and after film deposition. The deflection of the substrate by the deposited film is obtained by the phase map. Using the Zernike polynomial fitting algorithm, a three-dimensional contour map is generated from the polynomial coefficients to visualize the deformation of the thin film and to examine the tensile or compressive stress after film deposition. Four oxide films prepared by ionbeam sputter deposition are investigated for their film stresses. The experimental results show that the stress values are concordant with measurements using other methods.

ISSN:0950-0340    

DOI:10.1080/09500340008235094

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Usually it is assumed that the stimulated emission appears as a consequence of the Bose—Einstein statistics of photons and that to observe this effect at least two excitations have to be initially present in the atom—field system. That is, both the atom and the electromagnetic field have to be excited. In this paper we show that stimulated emission can appear exclusively as a consequence of quantum interference in a system with just a single excitation. Specifically, we consider a single two-level atom which is initially in its lower energy state and it interacts with a single-photon multi-mode wave packet. We show that for a proper choice of the photon-wave packet the atom can exhibit stimulated emission.

ISSN:0950-0340    

DOI:10.1080/09500340008235095

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We report the appearance of circular birefringence (optical activity) in amorphous side-chain azobenzene polymer films on illumination with circularly polarized light. The effect is observed only if an optical axis is previously created in the film with the help of linearly polarized light. The photoinduced optical activity is believed to be due to changes in the polymer structure initiated by a circular momentum transfer from the circularly polarized light to the azobenzene chromophores.

ISSN:0950-0340    

DOI:10.1080/09500340008235096

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The photorefractive holographic recording is a dynamic grating formulation process, where the grating is induced by the interference modulation of two beams, and the energies of the beams are exchanged with each other owing to their interaction in the induced grating. The grating modulation envelope is a comprehensive analysis for holographic dynamic recording and non-destructive readout, but analytic solutions can only be obtained by simultaneously solving the materials equations and the coupled wave equations. In this paper, based on Kukhtarev's model and Moharam's field function exact steady-state analytic expressions for dynamic grating envelopes are deduced for any constant values of light modulation depth and light excitation efficiency. Thus their approximations for straight formulation instead of parametric formulation are then obtained. These steady-state analytic solutions to envelopes describe the dynamic holographic recording and readout more clearly and exactly.

ISSN:0950-0340    

DOI:10.1080/09500340008235097

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

It is experimentally and numerically shown that a simple binaryphase optical element can be used for levelling the light energy in the focal plane of the focused Gaussian beam, generating a square-shaped focal beam, and transforming the Gaussian beam into a uniform beam which preserves its radius at a definite length of its path.

ISSN:0950-0340    

DOI:10.1080/09500340008235098

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Using vector diffraction theory, we have addressed the issue of finding the pupil function when the rate of decay of the intensity in the vicinity of the Gaussian focus along the optical axis is prescribed. The problem posed here reduces to a Fredholm integral equation, which is then solved to obtain the pupil function. We show that the diffraction integrals, as formulated by Wolf, are invariant if they are expressed in terms of thezth (the direction of the optical axis) component of the unit normal to the aberrated wave front. This makes it possible to obtain the pupil function from the solution of the Fredholm integral equation. We present results for lenses with high numerical aperture and show that the depth of focus is significantly increased without any loss of transmitted energy. Results further indicate that the FWHM of the primary lobe is significantly narrower than the clear aperture.

ISSN:0950-0340    

DOI:10.1080/09500340008235099

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor