302 resultados para Radiation fields


Relevância:

20.00% 20.00%

Publicador:

Resumo:

An approximate analytical description for fundamental-mode fields of graded-index fibers is explicitly presented by use of the power-series expansion method, the maximum-value condition at the fiber axis, the decay properties of fundamental-mode fields at large distance from the fiber axis, and the approximate modal parameters U obtained from the Gaussian approximation. This analytical description is much more accurate than the Gaussian approximation and at the same time keep the simplicity of the latter. As two special examples, we present the approximate analytical formulas for the fundamental-mode fields of a step profile fiber and a Gaussian profile fiber, and we find that they are both highly accurate in the single-mode range by comparing them with the corresponding exact solutions.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Based on the Huygens-Fresnel diffraction integral and Fourier transform, propagation expression of a chirped Gaussian pulse passing through a hard-edged aperture is derived. Intensity distributions of the pulse with different frequency chirp in the near-field and far-field are analyzed in detail by numerical calculations. In the near-field, amplitudes of the intensity peaks generated by the modulation of the hard-edged aperture decrease with increasing the frequency chirp, which results in the improving of the beam uniformity. A physical explanation for the smoothing effect brought by increasing the frequency chirp is given. The smoothing effect is achieved not only in the pulse with Gaussian transverse profile but also in the pulse with Hermite-Gaussian transverse profile when the frequency chirp increases. (C) 2005 Elsevier B.V. All rights reserved.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Theoretical method to analyze three-layer large flattened mode (LFM) fibers is presented. The modal fields, including the fundamental and higher order modes, and bending loss of the fiber are analyzed. The reason forming the different modal fields is explained and the feasibility to filter out the higher order modes via bending to realize high power, high beam quality fiber laser is given. Comparisons are made with the standard step-index fiber. (c) 2006 Elsevier B.V. All rights reserved.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Starting from the Huygens-Fresnel diffraction integral, the field expressions of apertured polychromatic laser beams with Gaussian and Hermite-Gaussian transverse modes are derived. Influence of the bandwidth on the intensity distributions of the laser beams is analyzed. It is found that when the bandwidth increases, the amplitudes and numbers of the intensity spikes decrease and beam uniformity is improved in the near field and the width of transverse intensity distribution of the apertured beams decreases in the far field. Thus, the smoothing and narrowing effects can be achieved by increasing the bandwidth. Also, these effects are found in the laser beams with Hermite-Gaussian transverse modes as the bandwidth increases.(c) 2006 Elsevier Ltd. All rights reserved.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

We analyze the electromagnetic spatital distributions and address an important issue of the transmission properties of spherical transverse-electric (TE) and transverse-magnetic (TM) eigenmodes within a tapered hollow metallic waveguide in detail. Explicit analytical expressions for the spatital distributions of electromagnetic field components, attenuation constant, phase constant and wave impedance are derived. Accurate eigenvalues obtained numerically are used to study the dependences of the transmission properties on the taper angle, the mode as well as the length of the waveguide. It is shown that all modes run continuously from a propagating through a transition to an evanescent region and the value of the attenuation increases as the distance from the cone vertex and the cone angle decrease. A strict distinction between pure propagating and pure evanescent modes cannot be achieved. One mode after the other reaches cutoff in the tapered hollow metallic waveguide as the distance from the cone vertex desreases. (C) 2008 Optical Society of America

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Based on the 2 x 2 (electric field) cross-spectral density matrix, a model for an electromagnetic J(0)-correlated Schell-model beam is given that is a generalization of the scalar J(0)-correlated Schell-model beam. The conditions that the matrix for the source to generate an electromagnetic J(0)-correlated Schell-model beam are obtained. The condition for the source to generate a scalar J(0)-correlated Schell-model beam can be considered as a special case. (C) 2008 Optical Society of America

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Fluorophosphate glasses with different contents of ErF3 were prepared. Due to the radiation trapping of Er, concentration dependence of the fluorescence lifetime is subject to distortion, and the stimulated-emission cross section calculated by the Fuchtbauer-Ladenburg equation is underestimated. The influence of radiation trapping on the measured fluorescence lifetime and width are investigated quantitatively. By comparing the intensity ratio of the 1556-1532 nm peak in the fluorescence spectrum with that in the stimulated-emission cross-section spectrum obtained according to the McCumber theory, the distortion ratio of fluorescence spectrum due to radiation trapping is obtained. An empirical way to quantitatively evaluate the influences of radiation trapping on fluorescence lifetime and width is proposed. (c) 2007 Optical Society of America.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Photoluminescence spectrum of Ce:YAG single crystal was studied employing vacuum ultraviolet (VUV) synchrotron radiation. Intrinsic absorption edge at about 52,000 cm(-1) was observed in the absorption spectrum. From the VUV excitation spectrum, the energy of the highest d-component of 53,191 cm(-1) (188 nm) for the Ce3+ ions in YAG was obtained at 300 K. The disappearance of the third 5d level at 37,735 cm(-1) (265 nm) in absorption and excitation spectra in our samples may be due to the impurity Fe3+ ions absorption. (C) 2006 Elsevier Ltd. All rights reserved.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Temperature fields of 355 nm high-reflectance (HR) coatings were investigated based on the interface absorption model. It was found that the highest temperature in the HR coatings increased with an increase in the extinction coefficient of the interface A, B, C, Al2O3 and MgF2. The highest temperature of HR coatings that can be reached increased quickly with the increase in the extinction coefficient of interface A in particular. The temperature rises of 355 nm HR coatings at different layers and different deposition temperatures were investigated based on experiments also. The damage mechanism of 355 nm HR coatings was confirmed with temperature fields and the interface absorption model.