多模光纤产生用于大气光通信的部分相干光源

 克服大气湍流对近地大气光通信质量影响,可归结为在接收端的照明均匀化,而采用部分相干光照明则是提高照明均匀性的一种有效途径。提出利用多模光纤的模间色散产生一个具有部分相干光特性的合成光源的方法,分析了该光源的产生原理,表明光束发散角由光纤芯径和发射透镜的焦距决定,由模间色散产生的光程差越大,该合成光源的空间相干性越差。仿真结果表明形成1 mrad远场发散角的合成光源是可行的,因而适于在空间光通信中应用。     

X射线高空间分辨多色显微成像系统研制及应用

在激光间接驱动惯性约束聚变(ICF)领域中,获得具有极高空间分辨率(优于5μm)的X射线辐射图像,是研究烧蚀不稳定性、内爆流线等关键物理过程的数据基础。基于掠入射反射式成像原理的Kirkpatrick-Baez(KB)显微成像系统作为一种具有高空间分辨率和集光效率的X射线显微诊断设备,目前已成为国际ICF装置的X射线关键诊断设备。在神光Ⅱ和神光Ⅲ原型装置条件上开展了KB诊断技术及设备的研究,在KB系统的光学设计、光学元件和物镜与系统装调技术等方面取得了许多重要进展,研制了大视场KB、多色KB等高分辨率X射线显微成像系统。这些系统已应用于我国的ICF内爆芯部发光和流线测量、流体不稳定增长测量等实验中,为关键物理量的测量提供了高空间分辨率的清晰图像。     

光学合成孔径成像技术计算机仿真与实验验证

首先阐明了光学合成孔径成像系统的原理。合成孔径成像系统在获得高截止频率的同时,降低了系统的中频性能,并且合成孔径成像系统的信息获取在方向上具有可选择性。然后对合成孔径成像系统的点扩散函数和光学传递函数进行了计算机仿真,仿真结果与合成孔径系统的成像原理一致。最后通过对辐射靶标的成像实验,再次对合成孔径成像系统的特性进行了验证。     

Soliton switching in inhomogeneous nonlocal media

We address a simple way to achieve routing of optical spatial solitons via soliton interactions in the inhomogeneous nonlocal media. We reveal that the variation of the nonlocality disturbs the solitons pairs and splits them into two individual solitons which have the same escape angle but opposite deflection directions. In particular, the escape angle monotonically increases with the increase of the nonlocality variation rate. We demonstrate that the soliton pairs could form self-consistent waveguides that are able to controllably guide a weak signal by any output positions.     

Theoretical study of broadband near-field optical spectrum of twisted bilayer graphene

We theoretically study the broadband near-field optical spectrum of twisted bilayer graphene (TBG) at various twist angles near the magic angle using two different models. The spectrum at low Fermi energy is characterized by a series of peaks that are almost at the same energies as the peaks in the far-field optical conductivity of TBG. When the Fermi energy is near a van Hove singularity, an additional strong peak appears at finite energy in the near-field spectrum, which has no counterpart in the optical conductivity. Based on a detailed calculation of the plasmon dispersion, we show that these spectroscopic features are associated with interband and intraband plasmons, which can provide critical information about the local band structure and plasmonic excitations in TBG. The near-field peaks evolve systematically with the twist angle, so they can serve as fingerprints for identifying the spatial dependent twist angle in TBG samples. Our findings pave the way for future experimental studies of the novel optical properties of TBG in the nanoscale.     

基于合成波长法的飞秒激光外差干涉测距方法

本文提出了一种基于合成波长法的飞秒激光外差干涉测距方法.系统采用两个带通滤波器产生两个具有一定波长差的单波长,用于产生合成波长.本方法结构简单,能量利用率高.与双频激光干涉仪在40 mm范围内的比对结果表明,该方法比对残差的标准差为91 nm.     

Spatial diffusion in a periodic optical lattice: revisiting the Sisyphus effect

We numerically study the spatial diffusion of an atomic cloud experiencing Sisyphus cooling in a three-dimensional linlin optical lattice in a broad range of lattice parameters. In particular, we investigate the dependence on the size of the lattice sites which changes with the angle between the laser beams. We show that the steady-state temperature is largely independent of the lattice angle, but that the spatial diffusion changes significantly. It is shown that the numerical results fulfill the Einstein relations of Brownian motion in the jumping regime as well as in the oscillating regime. We finally derive an effective Brownian motion model from first principles which gives good agreement with the simulations. Received 8 August 2001 and Received in final form 6 November 2001     

An improved Schlieren method for the sensitive and spatially resolved measurement of the quality of optical crystals with small apertures

We present an improved Schlieren method to measure the optical quality of crystals, defined by it’s optical homogeneity and the surface roughness of it’s facets. The method is based on a combination of Schlieren, interferometric and tilting angle measurements. It is especially appropriate for the optical characterization of crystals with small clear apertures. The theory and an application of this improved technique on a BIBO crystal are given. Spatial resolution and sensitivity of the method are mainly defined by the Schlieren setup, which offers a spatial resolution as high as 27 μm and a minimum deflection angle as low as 2.3×10^-6. PACS 81.70.Fy; 78.20.Ci; 42.25.Hz     

Angular and radial mode analyzer for optical beams

We describe an approach to determining both the angular and the radial modal content of a scalar optical beam in terms of optical angular momentum modes. A modified Mach-Zehnder interferometer that incorporates a spatial rotator to determine the angular modes and an optical realization of the fractional Hankel transform (fHT) to determine the radial modes is analyzed. Varying the rotation angle and the order of the fHT produces a two-dimensional (2D) interferogram from which we extract the modal coefficients by simple 2D Fourier analysis.     

Quantum Dots Luminescence Collection Enhancement and Nanoscopy by Dielectric Microspheres

In recent years, dielectric microspheres have been used in conjunction with optical microscopes to beat the diffraction limit and to obtain superresolution imaging. The use of microspheres on quantum dots (QDs) is investigated, for the first time, to enhance the light coupling efficiency. The enhancement of the QD luminescence collection in terms of extraction and directionality is demonstrated, as well as the enhancement of spatial resolution. In particular, it is found that a dielectric microsphere, placed on top of an epitaxial QD, increases the collected radiant energy by about a factor of 42, when a low numerical aperture objective is used. Moreover, if two or more QDs are present below the microsphere, the modification of the far field emission pattern allows selective collection of the luminescence from a single QD by simply changing the collection angle. Dielectric microspheres present a simple and efficient tool to improve the QD spectroscopy, and potentially QD-based devices.     

飞秒激光与固体靶相互作用中光辐射时间特性的实验研究

为了探索光辐射的时间特性, 在100 TW掺钛蓝宝石飞秒激光器上利用光学条纹相机, 分别在靶背表面法线方向测量了光辐射的时间积分和时间分辨成像光斑. 实验测量结果显示: 光辐射时间积分成像光斑呈长条状, 而辐射区域有发散角、有光强分布, 包含多种辐射成分; 光辐射的时间分辨成像光斑进一步证明, 渡越辐射(TR) 是信号强而快, 持续时间短, 为皮秒(ps) 量级, 是最先到达屏幕上, 并推算出相应的持续时间为85.5ps. 其他成分光辐射是信号弱而慢, 持续时间长, 为纳秒(ns) 量级, 是最后到达屏幕上. 光辐射的时间特性能为鉴别和判断TR信号提供了新的依据.     

BaTiO3晶体中光束自陷的理论研究

对聚焦光束通过有一定外加电场ＢａＴｉＯ３晶体时的自陷现象进行了理论分析，发现在正切割晶体中观察空间孤子是不合适的，因仅利用了很微小的电光系数γ３３。对异型切割情况进行了讨论，给出了维持光束自陷的外加电场范围和实际观察的最佳角度。     

具有存储功能的衍射图像光刻系统的研制

研制了一种在衍射光变图像器件上进行信息存储的新型数字化激光光刻系统。采用空间光调制器作图形自动输入,双远心投影成像系统在光刻记录面上缩微图形。通过光栅干涉光学头对记录面上的微图形进行干涉调制,使微图形上产生干涉条纹,条纹空间频率范围为500-1200lp／mm。在光刻胶干版上的存储实验表明,在衍射光变图像上的单角度存储信息密度大于3．7Mbit／cm^2。改变干涉条纹取向、条纹间隔和需要存储的图形,光刻系统可实现信息的旋转复用存储。上述光刻系统将会在防伪和衍射光变图像器件制造领域有良好应用。     

Optical spatial solitons supported by photoisomerization nonlinearity in a polymer

We present a theory for a new type of optical spatial soliton that is based on the angle hole burning mechanism of photoisomerization in some polymers. We predict that the photoisomerization nonlinearity can support steady-state dark and bright spatial solitons in the polymer. We also discuss the dependence of the FWHM of the spatial soliton on wavelengths of the background beams and on the ratio of the intensity of the background beam to that of the signal beam.     

衍射受限光学合成孔径成像系统像质评价

简述了光学合成孔径成像系统的原理,合成孔径成像系统在获得高截止频率的同时,降低了系统的中频性能,在空域表现为点扩展函数次峰增加。然后运用两点分辨率和光学传递函数对衍射受限光学合成孔径成像系统的像质评价问题进行了分析,指出了瑞利判据、斯派罗准则和“门限”判据的不足,认为当点扩展函数次峰大于主峰的0．5倍时,合成孔径系统与单孔径系统相比将失去优势。以光学传递函数为标准。分析三孔径合成系统子孔径尺寸、相互间距与等效系统孔径尺寸之间的关系。当子孔径直径不变时,随着其所在圆半径的增大,实际截止频率先增大,然后减小。     

Tunable enhanced spatial shifts of reflective beam on the surface of a twisted bilayer of hBN

We investigated Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts of a reflective beam on a twisted bilayer of hexagonal boron nitride (hBN), where a left circularly polarized beam was incident on the surface. Our results demonstrate that the twist angle between the two optical axes plays an important role in obtaining large shifts with a high reflectivity. The GH shift with 10λ₀ is achieved, while the reflectivity is near 100% by tuning the twist angle. The maximum of the IF shift is found in the certain condition satisfied by the reflective coefficients, and the shift strongly depends on the twist angle between the optical axes of the two slabs. The spatial shifts obtained directly from the GH and IF shift definitions were provided, which indicate that the theoretical results from the stationary phase method are believable. These results may open up a new way for developing the nano-optical devices.     

Nonspecular total internal reflection of spatial solitons at the interface between highly birefringent media

We investigate total internal reflection of nonlocal spatial optical solitons at the interface between two differently oriented regions of a highly birefringent nematic liquid crystal. The solitons survive the interaction with an induced index mismatch and undergo nonspecular reflection, with an emerging angle differing appreciably from the incidence angle.     

Complex interaction of polarized light with three-dimensional opal-based photonic crystals: Diffraction and transmission studies

Polarization characteristics of light interaction with the photonic crystal of a-SiO₂ synthetic opals were studied under the conditions of low dielectric contrast. We analyzed 3D diffraction patterns of monochromatic light and calculated optical transmission spectra of oriented samples. The diffraction patterns are found to change with the polarization of incident light, indicating a strong polarization dependence of photonic stop bands in synthetic opals. It is shown theoretically there exists a critical angle, θ_c, of the p-polarized light incident on the (h k l) crystal plane, at which the resonance contribution to Bragg diffraction vanishes.     

SIL-based confocal fluorescence microscope for investigating individual nanostructures

We developed a fluorescence confocal microscope equipped with a hemispherical solid immersion lens (SIL) and apply it to study the optical properties of light-harvesting complexes. We demonstrate that the collection efficiency of the SIL-equipped microscope is significantly improved, as is the spatial resolution, which reaches 600 nm. This experimental setup is suitable for detailed studies of physical phenomena in hybrid nanostructures. In particular, we compare the results of fluorescence intensity measurements for a light-harvesting peridinin-chlorophyll-protein (PCP) complex with and without the SIL.