Propagation properties of a partially polarized electromagnetic twist anisotropic Gaussian Schell-model beam in turbulent atmosphere

Based on the extended Huygens-Fresnel integral formula, analytical formulae for the elements of cross-spectral density matrix of partially polarized electromagnetic twist anisotropic Gaussian Schell-model (TAGSM) beam propagating in turbulent atmosphere can been derived by a tensor method. Our main attention was focus on the effect of the atmospheric turbulence, twist parameters and partial coherence on the spectral degree of polarization, the spectral degree of coherence and the spectral density. Numerical calculation results and analysis are given.     

Spectral properties of apertured stochastic electromagnetic twist anisotropic Gaussian Schell-model beam propagating in turbulent atmosphere

Based on the extended Huygens-Fresnel principle, analytical formulas are derived for the cross-spectral density matrix of an apertured stochastic electromagnetic twist anisotropic Gaussian Schell-model (ETAGSM) beam propagating in a turbulent atmosphere by use of a tensor method. Spectral properties of apertured ETAGSM beam are closely related with the strength of atmospheric turbulence, the aperture widths and the beam's parameters, etc. Our main attention was focused on the influence of the aperture widths, atmospheric turbulence, twist parameters and partial coherence on the spectral properties (including spectral degree of polarization, the spectral degree of coherence and the spectral density) of apertured ETAGSM beam propagating in turbulent atmosphere. Numerical calculation results and analysis are given.     

Amplitude and phase control of spontaneous emission in a double-driven four-level atom

The spontaneous emission property of a coherent microwacve-driven four-level atomic system is investigated. It is shown that a few interesting phenomena due to microwave generated coherence (MGC) such as spectral narrowing, partial cancellation, and spectral-line enhancement can be achieved by varying the Rabi frequency and the phase of microwave field coupling the two upper levels in the atomic system.     

Changes in the spectral degree of coherence and spectral intensity of spatially and spectrally partially coherent cosh-Gaussian pulsed beams in free space

The analytical expressions for the spectral degree of coherence and spectral intensity of spatially and spectrally partially coherent cosh-Gaussian pulsed (ChGP) beams propagating in free space are derived. It is shown that the spectral degree of coherence and spectral intensity of spatially and spectrally partially coherent ChGP beams depend on the spatial correlation parameter, decentered parameter and temporal coherence length. Depending on the decentered parameter, the effective width of the spectral degree of coherence can be larger than, smaller than or equal to that of the spectral intensity. The results are illustrated by numerical examples.     

Spatial structure of the degree of coherence for broadband dispersed laser beams

1D and 2D spatial distributions of a complex degree of coherence are obtained using numerical simulation for the broadband dispersed laser beams. The configuration of the spatial inhomogeneities (speck-les) of the degree of coherence is studied at various spectral widths and dispersions of the beam. It is shown that the speckle size increases with increasing distance from the initial plane where the light field is assumed to be spatially coherent. The small- and large-scale structures of the degree of coherence are shown for the transverse cross section of the beam. The results are compared with the analytically calculated correlation functions of the spatial coherence. The features of the speckle structure are interpreted using the concept of partial speckles.     

Changes in the spectrum, polarization, and coherence of stochastic spatially and spectrally partially coherent electromagnetic J0-correlated Schell-model pulsed beams propagating in free space

Taking the stochastic electromagnetic J ₀-correlated Schell-model pulsed (JSMP) beam as a typical example of stochastic spatially and spectrally partially coherent electromagnetic pulsed beams, the analytical expressions for the cross-spectral density matrix, spectral density, spectral degree of polarization and spectral degree of coherence of stochastic electromagnetic JSMP beams propagating in free space are derived, and used to study the changes in the spectrum, polarization, and coherence of stochastic spatially and spectrally partially coherent electromagnetic JSMP beams. It is shown that the on-axis spectrum is blue-shifted in free-space propagation and is dependent on the pulse temporal coherence length and spatial correlation parameter. The distribution of the on-axis spectral degree of polarization depends on the frequency and spatial correlation parameter. The spectral degree of coherence increases with increasing pulse temporal coherence length. The results derived are interpreted physically.     

四个部分相干点源的完全相消干涉特性

使用部分相干光的干涉定律,对部分相干光照明呈正方形对称四孔干涉仪的干涉场做了研究.结果表明,一定条件下,可出现完全相消干涉,并存在光强和光谱相干度的相位奇点.与二个、三个部分相干点源的干涉做了比较.对所得结果物理上可解释为：虽然四个点源是部分相干的,但从两个点源出射场之和与从另外两个点源出射场之和却可能是完全相关的. 关键词： 相关奇点光学 完全相消干涉 部分相干光 刃型位错线     

部分相干修正贝塞尔高斯光束通过光阑透镜的光谱特性

基于部分相干光的传输理论,研究了部分相干修正贝塞尔高斯光束（MBGB）通过光阑透镜系统后,轴上光谱位移及光谱开关.数值计算结果表明,光谱开关主要与截断参量、光束菲涅耳数以及光谱相干度有关.光谱开关的个数随着光束菲涅耳数以及截断参量的增大将增多,而随光谱相干度的增大而减少.但当截断参量增大到一定值时,光谱开关将消失.例如,当光谱相干度取0.5时,截断参量大于2.2,光谱开关将消失,仅表现出蓝移.     

部分相干涡旋光束在大气湍流中的远场传输特性

运用广义惠更斯-菲涅耳原理,详细研究了部分相干涡旋光束在湍流介质中的远场传输规律.研究表明,部分相干涡旋光束的光谱相干度及光强分布与光束的拓扑电荷数、空间相对相干长度及湍流介质的折射率结构常数等因素有关.在湍流介质中,光谱相干度存在相位奇点,并且随着空间相对相干长度的增大,相干涡旋逐渐演化为强度涡旋,而湍流介质的强弱对部分相干涡旋光束的影响则相反,随着湍流介质的折射率常数的增大,强度涡旋逐渐演化为相干涡旋.     

Beam radiated from quasi-homogeneous uniformly polarized electromagnetic source scattering on quasi-homogeneous media

We study the coherence properties of the field generated by beam radiated from quasi-homogeneous (QH) electromagnetic source scattering on QH media. Formulas for the spectral density and spectral degree of coherence of the three dimensional scattered field are derived. The results show under assumption that the diagonal correlation coefficients of the source are proportional to each other, the far field of the scattered light satisfy two reciprocity relations analogous to that in the scalar case, that, the spectral density is proportional to the convolution of the spectral density of the source and the spatial Fourier transform of the correlation coefficient of the scattering potential; the spectral degree of coherence is proportional to the convolution of the diagonal correlation coefficients and the strength of the scattering potential.     

Spatial correlation properties and the spectral intensity distributions of focused Gaussian Schell-model array beams

The spatial correlation properties and the spectral intensity distributions of focused Gaussian Schell-model (GSM) array beams are studied in detail. The closed-form expressions for the spectral degree of coherence and the spectral intensity of focused GSM array beams are derived. It is shown that the spectral degree of coherence of focused GSM array beams is the same as that of focused GSM beams in the focal plane. On the other hand, it is found that, in the focal plane the spectral intensity distribution of focused GSM array beams is the fringe pattern when the value of the coherence length is small. However, it becomes one peak located at the center as the value of the coherence length is large enough. In the focal plane, the spectral intensity maximum increases and the width of the normalized spectral intensity distribution decreases as the beam number increases. In general, for GSM array beams, the width of the modulus of the spectral degree of coherence in the focal plane always exceeds that of the normalized spectral intensity distribution, which is different from the behavior of focused GSM beams. In addition, the power in the bucket (PIB) and the beam propagation factor (M² factor) are also discussed. The main results are explained physically.     

A study of the relaxation dynamics in a quadrupolar NMR system using Quantum State Tomography

This article reports a relaxation study in an oriented system containing spin 3/2 nuclei using quantum state tomography (QST). The use of QST allowed evaluating the time evolution of all density matrix elements starting from several initial states. Using an appropriated treatment based on the Redfield theory, the relaxation rate of each density matrix element was measured and the reduced spectral densities that describe the system relaxation were determined. All the experimental data could be well described assuming pure quadrupolar relaxation and reduced spectral densities corresponding to a superposition of slow and fast motions. The data were also analyzed in the context of Quantum Information Processing, where the coherence loss of each qubit of the system was determined using the partial trace operation.     

Can two partially coherent cosh-Gaussian beams generate far fields with the same spectral degree of coherence？

Taking partially coherent cosh--Gaussian (ChG) beams as an example of more general partially coherent beams, we have studied the spectral degree of coherence of partially coherent ChG beams in the far field. It is shown that, unlike Gaussian Schell-model (GSM) beams, in the strict sense there do not exist two partially coherent ChG beams which can generate far fields with the same spectral degree of coherence. However, under certain conditions it is possible to find two partially coherent ChG beams with the same spectral degree of coherence in the far field.     

Coherence vortices of partially coherent beams in the far field

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.     

Stokes parameters and polarization contrasts in Young's interference experiment

We derive a spectral interference law that governs the behavior of the four Stokes parameters in Young's two-pinhole experiment with a random electromagnetic beam. In addition to the visibility of intensity fringes, we introduce three new contrast parameters that describe the interference-induced changes in the field's state of partial polarization. The polarization modulation depends on the electric field correlations at the pinholes and is closely related to the two-point Stokes parameters. The results are expected to be particularly useful in polarization interferometry and electromagnetic coherence theory. The formalism is demonstrated with specific examples.     

Phase singularities of the coherence functions in Young's interference pattern

We analyze the coherence properties of a partially coherent field emerging from two pinholes in an opaque screen and show that the spectral degree of coherence possesses phase singularities on certain surfaces in the region of superposition. To our knowledge, this is the first illustration of the singular behavior of the spectral degree of coherence, and the results extend the field of singular optics to the study of phase singularities of correlation functions.     

部分相干涡旋光束形成的相干涡旋特性研究

推导出部分相干涡旋平顶光束的传输解析公式,并用以研究了聚焦场和自由空间中部分相干涡旋光束形成相干涡旋的特性.结果表明,相干涡旋与光束阶数N,空间相干参数α和参考点位置(x1,y1)有关.依赖于参考点的选择,光谱相干度可能存在零值点,也可能没有零值点.特别是,若选取x1=y1=0,光谱相干度零值点处的位相可以是确定的,因而不存在相干涡旋.     

Spectral shaping to improve the point spread function in optical coherence tomography

We demonstrate inhibition of the sidelobes of the axial point spread function in optical coherence tomography by shaping the power spectrum of the light source with a remaining power of 4.54 mW. A broadband amplified spontaneous emission source radiating at 1565 +/- 40 nm is employed in a free-space optical coherence tomography system. The axial point spread functions before and after optical spectral shaping are presented. Results show that spectral shaping of the source can inhibit sidelobes of the point spread function up to 12.9 dB, with an associated small increase of 2.2 dB in noise floor in the far field. The effect of spectral shaping on axial resolution is demonstrated according to three metrics. Image quality improvement is also illustrated with optical coherence tomography images of an onion before and after spectral shaping.     

Full Bandwidth Measurement of Supercontinuum Spectral Phase Coherence in Long Pulse Regime

Abstract

This article reports that spectral phase coherence in the supercontinuum in long pulse regime can be measured simply and effectively by using an interference technique with the help of a Mach–Zehnder interferometer. It is also demonstrated that chromatic dispersion on the fringe visibility of interference spectral patterns is overcome in the setup. The technique is applied to characterize supercontinuum spectral phase coherence in a highly non-linear optical fiber with different input conditions: unseeded, coherent seeded, and incoherent seeded picosecond pumps. The results confirm the phase coherence characteristic predicted theoretically in previous studies.     

Study on the spatial coherence of vortex Gaussian beams passed atmospheric turbulence

In this paper, the spectral degree of coherence formula was derived by using the generalized Huygens–Fresnel principle and the method of Rytov phase structure function quadratic approximation. The spatial coherence of vortex Gaussian beams passed atmospheric turbulence was studied. It showed that the spatial coherence was mainly affected by the coherence of light source, the number of topological charges and the transmission distance. The distance of transmission was farther, the spatial coherence of beam was better. The number of topological charges were more, the spatial coherence of beam was better. In a certain transmission distance, the coherence of light source was better, the spatial coherence of beam was worse. In addition, there were coherent vortexes which spectral degree of coherence was zero after the partially coherent vortex beams getting through atmospheric turbulence transmission.