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This paper derives explicit expressions for the propagation of Gaussian beams carrying two vortices of equal charges m=±1 diffracted at a half-plane screen, which enables the study of the dynamic evolution of vortices in the diffraction field. It shows that there may be no vortices, a pair or several pairs of vortices of opposite charges m=+1, -1 in the diffraction field. Pair creation, annihilation and motion of vortices may appear upon propagation. The off-axis distance additionally affects the evolutionary behaviour. In the process the total topological charge is equal to zero, which is unequal to that of the vortex beam at the source plane. A comparison with the free-space propagation of two vortices of equal charges and a further extension are made. 相似文献
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The concept of partially coherent nonparaxial modified Bessel--Gauss (MBG)
beams is proposed. Based on the generalized Rayleigh-Sommerfeld diffraction
integral, the analytical propagation equations of nonparaxial MBG beams in
free space are derived and analysed, and some special cases are discussed.
In particular, under the paraxial approximation our results reduce to the
corresponding paraxial ones. Numerical calculation examples are given to
illustrate the dependence of intensity and spectral degree of coherence on
the beam order $m$, \textit{$\xi $} and $f$ parameters, and to compare
the difference between the paraxial and nonparaxial results. 相似文献
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Anomalous spectral behaviour of diffracted chirped Gaussian pulses in the near field 总被引:1,自引:0,他引:1 下载免费PDF全文
By using the Fourier transform method, analytical expressions for the axial power spectrum and near-field intensity in the spacetime domain of chirped Gaussian pulses diffracted at an aperture are derived, which permit us to study changes in spectral and temporal profiles of the chirped Gaussian pulses both analytically and numerically. Detailed numerical results and physical analysis show that spectral anomalies take place in the neighbourhood of certain critical distances, and the shifting of maximum and splitting of temporal intensity profiles appear. In particular, for ultrashort chirped pulses, there exists also spectral switch. Besides the truncation parameter, the chirp parameter and pulse duration affect the behaviour of spectral switches. 相似文献
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Based on the propagation law of cross-spectral density function,
studied in this paper are the coherence vortices of partially
coherent, quasi-monochromatic singular beams with Gaussian
envelope and Schell-model correlator in the far field, where our
main attention is paid to the evolution of far-field coherence
vortices into intensity vortices of fully coherent beams. The
results show that, although there are usually no zeros of
intensity in partially coherent beams with Gaussian envelope and
Schell-model correlator, zeros of spectral degree of coherence
exist. The coherence vortices of spectral degree of coherence
depend on the relative coherence length, mode index and
positions of pairs of points. If a point and mode index are kept
fixed, the position of coherence vortices changes with the
increase of the relative coherence length. For the low coherent
case there is a circular phase dislocation. In the coherent
limit coherence vortices become intensity vortices of fully
coherent Laguerre--Gaussian beams. 相似文献
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本文建立了有限几何尺寸板条激光介质的三维温度分布模型.在普遍情况下,推导出温度分布的解析式.由此便于分析板条温度分布和泵浦参数、激光介质等的依赖关系.借助计算机进行的数值计算,证实了理论结果. 相似文献