Display of spatial coherence

The mutual-intensity function plays a major role in characterizing quasi-monochromatic, partially coherent optical signals. We demonstrate an optical system for displaying the mutual intensity of a one-dimensional input beam. The experimental system is based on the fact that the mutual intensity of a signal can be expressed as the ensemble averaging of a cross-correlation operation between two related optical signals. The setup consists of a Sagnac interferometer followed by an optoelectronic joint transform correlator. Experimental results demonstrate the capabilities of the mutual-intensity analyzer.     

Beam shaping by spatial coherence modulation based on spatial coherence wavelets

A novel technique for designing specific shapes of power distributions is presented. It bases on the modulation of the spatial coherence of the optical field in amplitude and phase. The modulating functions are synthesized from the phase-space diagram of the field, provided by the marginal power spectrum. Numerical results for the phase modulation of the complex degree of spatial coherence are presented. This beam shaping technique is suitable in applications that require specific shapes and sizes.     

光学空间相干度双稳态

本文首次提出一种由相干度非线性调制得到的新型光学双稳态——空间双稳态及其作用无耦合和有交叉耦合情况下,经γ/υ和υ/ν变换反馈可得到多种形式的双稳态,且给出了几种情况下的稳态特性方程、参数选择区域以及翻转条件等.     

Enhancement of spatial coherence by surface plasmons

We report on a method to generate a stationary interference pattern from two independent optical sources, each illuminating a single slit in Young's interference experiment. The pattern arises as a result of the action of surface plasmons traveling between subwavelength slits milled in a metal film. The visibility of the interference pattern can be manipulated by tuning the wavelength of one of the optical sources.     

Role of spatial coherence in polarization tomography

We analyze an experimental setup in which a quasi-monochromatic spatially coherent beam of light is used to probe a paraxial optical scatterer. We discuss the effect of the spatial coherence of the probe beam on the Mueller matrix representing the scatterer. We show that, according to the degree of spatial coherence of the beam, the same scattering medium can be represented by different Mueller matrices. This result should serve as a warning for experimentalists.     

Effects of spatial coherence on near-field spectra

Expressions are derived for the spectrum of the field generated by a planar, homogeneous, secondary source of any spectral distribution and of any state of spatial coherence. It is shown that the state of coherence affects the contributions of the homogeneous as well as the evanescent waves of the emitted field. The near-field spectra are studied in detail. The analysis is illustrated by examples.     

Ultrahigh-resolution full-field optical coherence tomography using spatial coherence gating and quasi-monochromatic illumination

We developed an ultrahigh-resolution full-field optical coherence tomography (FF-OCT) microscope that is based on the spatial, rather than the temporal, coherence gating. The microscope is capable of observing three-dimensional microbiological structures as small as 0.4 μm × 0.4 μm × 1.0 μm (xyz) using quasi-monochromatic light and a liquid crystal retarder. Unlike traditional FF-OCT systems, this microscope can be operated in high resolution for any preferable wavelength with minimized defocusing and dispersion effects. High-resolution images of an onion cell are presented.     

激光空间相干性对照明均匀性的影响

研究了激光相干性对照明均匀性的影响,为照明激光器的选择提供了理论参考。其中,部分相干高斯光束分解为模式间相互独立的厄米-高斯光束的迭加。采用相位屏的近似处理方法对激光通过大气湍流的传输进行计算模拟。数值模拟的结果表明：当照明光束的空间相干性降低时,其照明均匀度逐步提高。因此对于照明激光器而言,选择空间相干性较差的激光器对其照明均匀度更加有益。     

激光空间相干性对照明均匀性的影响

 研究了激光相干性对照明均匀性的影响，为照明激光器的选择提供了理论参考。其中，部分相干高斯光束分解为模式间相互独立的厄米-高斯光束的迭加。采用相位屏的近似处理方法对激光通过大气湍流的传输进行计算模拟。数值模拟的结果表明：当照明光束的空间相干性降低时，其照明均匀度逐步提高。因此对于照明激光器而言，选择空间相干性较差的激光器对其照明均匀度更加有益。     

Longitudinal purely spatial coherence of a light field

The effects of longitudinal purely spatial coherence of light and the results of observation of these effects in an interference experiment are considered under the condition that the length of temporal coherence l _c is considerably smaller than the length of longitudinal spatial coherence ρ_‖ of the field. It is shown that, for l _c ? ρ_‖, the longitudinal purely spatial coherence of the light field in fact governs the coherence of the wave train in the process of its propagation. The length and the time of coherent (“free”) path of the wave train are considered as new spatial and temporal scales of a partially coherent light field.     

First direct measurement of the spatial coherence of sunlight

Direct sunlight is often deemed incoherent, hence unsuitable for antenna power conversion. However, all radiation exhibits spatial coherence when detected on a sufficiently small scale. We report the first direct measurement of the spatial coherence of solar beam radiation, achieved with a customized tabletop cyclic-shearing interferometer. Good agreement is found between experiment and theory, with promising ramifications for solar aperture antennas.     

基于空间相干性控制的环形光源技术

提出了一种利用二元相位光栅产生环形光源的新方法,并且可以实现环形光源的环半径和环厚度连续或固定可调。阐述了环形光源抑制相干噪声的原理,推导了环形光源半径及干涉腔长度与条纹对比度之间的关系。实验表明：环形光源能保持干涉条纹对比度,同时有效抑制相干噪声,环形光源模式系统的本征噪声峰谷值小于点光源模式,且没有明显牛顿环噪声,测量重复性和测量精度都高于点光源模式,从而提高了测量精度。     

The effect of spatial coherence of sound field on subspace-based high-resolution spatial spectrum estimation

When the signals received by any two array elements are not fully correlated, the performance of DOA (Direction Of Arrival) estimation methods might degrade if the plane-wave model assumption is still used. For narrowband uniform linear array, by utilizing the property of Toeplitz matrix, it is proved that the received signals can be expressed as the sum of several plane-wave signals, which can be viewed as the "splitting" parts of the true sources. The "splitting" of sources makes it difficult to estimate the true number of sources. As a result, spurious peaks might occur in the spatial spectrum when subspace-based high-resolution spatial spectrum estimation technique is used.     

光场空间相干性的测量方法及比较

本文归纳了基于分波前干涉原理的具有代表性的干涉测量方法——杨氏双孔干涉法、逆波前杨氏干涉法和非冗余孔径阵列干涉测量法,以及基于分振幅干涉原理的干涉测量方法——自参考干涉测量法;介绍了各种测量方法的工作原理、实验配置;比较了4种测量方法的优缺点,并给出每种方法的最佳应用领域。本文结论可为根据对空间相干性测量的不同要求,选择合适的测量方法提供初步参考。     

Impact of the spatial coherence on self-interference digital holography

Owing to the unique feature that the signal and reference waves of self-interference digital holography (SIDH) contain the same spatial information from the same point of object, compared with conventional digital holography, the SIDH has the special spatial coherence properties. We present a statistical optics approach to analyzing the formation of cross-correlation image in SIDH. Our study reveals that the spatial coherence of illumination light can greatly influence the imaging characteristics of SIDH, and the impact extent of the spatial coherence depends substantially on the recording distance of hologram. The theoretical conclusions are supported well by numerical simulation and optical experiments.     

Quantitative measurements of undiilator spatial coherence at the ALS

Modern synchrotron-based X-ray fluorescence microscopy (XFM) has become a critical tool for many a research program, addressing extremely broad and highly relevant scientific questions. Their ability to map trace elemental content and probe local chemical state has been applied to numerous scientific areas in the life sciences [1 Paunesku, T. 2006. J Cell Biochem, 99(6): 1489–502. [Crossref], [PubMed] , [Google Scholar]–3 Bohic, S. 2012. J Struct Biol, 177(2): 248–58. [Crossref], [PubMed] , [Google Scholar]], the environmental and earth sciences [4 Fittschen, U. E. A. and Falkenberg, G. 2011. Spectrochimica Acta Part B-Atomic Spectroscopy, 66(8): 567–580. [Crossref] , [Google Scholar], 5 Lombi, E. 2011. Analytical and Bioanalytical Chemistry, 400(6): 1637–1644. [Crossref], [PubMed] , [Google Scholar]], the materials sciences, as well as in cultural heritage studies. The newest generation of instruments utilizes high-brightness X-ray sources and incorporate state-of-the-art focusing optics and detector systems. Advances in X-ray sources and nanofocusing optics, for example, have allowed these instruments to achieve spatial resolutions of 20–30 nm using diffractive optics such as Fresnel zone plates and 200 nm using reflective optics such as Kirkpatrick-Baez mirrors. New beamlines, now in the design stage, aim to achieve similar (and better) resolutions within the next five years.     

Experimental study of coherence vortices: local properties of phase singularities in a spatial coherence function

By controlling the irradiance of an extended quasimonochromatic, spatially incoherent source, an optical field is generated that exhibits spatial coherence with phase singularities, called coherence vortices. A simple optical geometry for direct visualization of coherence vortices is proposed, and the local properties and the spatial evolution of coherence vortex are experimentally investigated. To our knowledge, this is the first direct and quantitative experimental measurement of a generic coherence vortex.