摘要:

A new method for measuring the inner scale and structure constant of atmospheric turbulence is proposed and tested. It utilizes both phase and amplitude fluctuations of laser radiation propagating in the medium. The measured quantities are the intensity variance of a spherical wave and the transverse-displacement variance (wandering) of a narrow laser beam. The method is developed within the limits of geometrical optics. Experimental laboratory results are presented. Values of inner scale of a few millimetres are measured.

ISSN:0950-0340    

DOI:10.1080/09500349014551731

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A time dependent theory of resonant degenerate four-wave mixing (DFWM) with broad bandwidth lasers is outlined and used to calculate the temporal evolution of DFWM signals generated by pulsed lasers. Experimental measurements of saturation-induced pulse-shortening and reshaping effects are reported for DFWM in atomic Na vapour and found to be in quantitative agreement with theoretical predictions.

ISSN:0950-0340    

DOI:10.1080/09500349014551741

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A numerical study is presented of the effective gain in degenerate two-wave mixing, for a reflection geometry in a photorefractive crystal. Apart from the so-called ‘shooting method’ we employ a simple explicit method of ‘finite differences’ to obtain numerical solutions of the nonlinear coupled-wave equations. A comparison between the two indicates that the computed results from the finite differences method are still in reasonable agreement with those obtained from the shooting method. At the same time the finite differences method is more straightforward and usually found to be faster than the shooting method for a small number of discrete points. The dependence of the effective gain on various parameters is shown at the saturation as well as non-saturation (i.e. below saturation) stage of the refractive-index modulation. A significant difference in gain is found to exist between these two regimes of modulation. Numerical results are compared and presented as graphs.

ISSN:0950-0340    

DOI:10.1080/09500349014551751

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The population dynamics of a four-level atom, with decay from the highest level, interacting with three arbitrarily intense laser fields is studied. In a previous paper [4], this four-level system was investigated with no decay included. For a specific set of input fields, it was found that substantial population could be transferred from the ground state to the highest excited state. In that study, the detunings required to obtain this maximum population transfer were not explained. In this present work, we have introduced a two-level atom model that explains this choice of detunings. They are such as to make the three fields resonant with the Stark-shifted

ISSN:0950-0340    

DOI:10.1080/09500349014551761

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

An ideal pulsed laser is placed on the axis of a disk-shaped receiver and aimed at the centre of the disk. The space between the laser and receiver disk is filled with an aerosol of isotropically scattering particles. Using a novel analytical technique that isnotbased on the familiar radiative transfer equation, we derive exact formulae for the time dependent singly-scattered power and the total singly scattered energy that is received by the disk. We find in particular that, in the limit of a vanishingly small receiver disk, the ratio of singly scattered to unscattered energy received isr0βs/2, wherer0is the radius of the receiver disk and βsis the scattering coefficient of the aerosol. This result is remarkable not only for its simplicity, but also because it implies that the singly scattered energy received by the small disk is proportional to thesquare rootof the area of the disk.

ISSN:0950-0340    

DOI:10.1080/09500349014551771

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

In this paper, two self-similar structures on a plane are designed, corresponding diffraction screens are made and their Fraunhofer patterns are given. Based upon a point of view of generative production, we have found the recurrence spectral formulae and plotted a series of spectral function curves. Finally some characteristics of the curves have been discussed. This investigation may be taken as an optical simulation for researching practical self-similar problems occurring in chaos.

ISSN:0950-0340    

DOI:10.1080/09500349014551781

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We describe a new robust approach for the analysis of strip gratings, both of finite and infinite conductivity, for the TE and TM cases. The field distributions in the plane of the grating are expanded in a Fourier series, whose coefficients are derived as the solution to an infinite-dimensional system of linear equations. Various configurations of the scatterer are considered and it is shown that even in cases where the Tsao-Mittra SIT procedures fails to converge and the moment method requires a large matrix to arrive at a solution, our method yields reasonable results even for small matrix sizes. The accuracy of the solution procedure is analysed by considering the mean-square error in the field magnitudes as a function of the truncation size of the infinite system of linear equations.

ISSN:0950-0340    

DOI:10.1080/09500349014551791

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The absorption and reflection of a plane wave at the interface of a linear dielectric and a very dense saturable absorber is studied in situations where the linear refractive index has an imaginary part that is much bigger than its real part. In this domain of parameters, computed results calculated without the use of the slowly varying envelope approximation show the presence of a self-reflected wave that eventually might lead to a bistable reflectivity.

ISSN:0950-0340    

DOI:10.1080/09500349014551801

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The third principle of group theoretical statistical mechanics is used to define the existence of many new nonlinear optical rotatory phenomena caused by the interaction of intense electromagnetic radiation with molecular ensembles. This treatment removes the necessity of having to distinguish between ‘natural’ and ‘magnetic’ optical activity; both processes emerge consistently from the analysis, which is based on an application of the Hellman-Feynman theorem and a double Taylor expansion of the induced electric and magnetic dipole moments.

ISSN:0950-0340    

DOI:10.1080/09500349014551811

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Quantum signals propagating in nonlinear media are studied with the anharmonic oscillator model. The results are used to calculate the information and the signal-to-noise ratio in binary optical communications which use those signals.

ISSN:0950-0340    

DOI:10.1080/09500349014551821

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor