“禁戒光”近场光学显微镜原理与系统

扫描近场光学显微术是８０年代后期发展起来的一种分辨率超过衍射极限的新型光学显微镜技术。本文介绍了国外最近出现的“禁戒光”近场光学显微镜系统的工作原理及结构。透射式ＳＮＯＭ中部分光沿着光轴向前传播；部分光沿着大于全内反射临界角的方向传播。前者称为允许光；后者称为禁戒光。应用“禁戒光”近场光学显微镜可同时获得三幅图像，即允许光像、禁戒光像和反映样品表面形貌的剪切力图像。禁戒光图像能够提供很好的对比度和分辨率。     

脉冲激光诱导光纤损伤的测试方法

 针对传能光纤的高峰值功率激光损伤过程，研究了光纤损伤测试方法。实验装置搭建中增加了定位孔，有利于激光注入光纤对准；分别采用刀口法和CCD法对入射光束不同截面处光斑大小进行了测量，两种方法的测量结果基本一致。参考GJB1487-92激光光学元件测试方法和ISO11245光学表面的激光诱导损伤阈值测试方法，采用N-ON-1损伤测试和有效光斑面积计算方法对芯径为400 μm的石英包层阶跃折射率石英光纤进行了损伤阈值测试。实验发现：光纤损伤部位全部为入射端面，利用200倍显微镜观察光纤端面，出现明显永久性损伤点。最后采用统计学原理和线性拟合等方法得出测试光纤的端面零概率损伤阈值为3.85 GW/cm²。     

On the spin fluctuation approach to the anderson and Kondo hamiltonians

The free energy expression of the full Anderson model is derived in a similar way as has been done before for the Kondo model. Use is made of the “asymptotic time approximation” first invented to study the x-ray threshold singularity. Again the procedure leads to a classical Coulomb gas on a ring. The magnetic field is included and plays the role of an electric field for the Coulomb gas. Further it turns out that the “symmetric” Anderson model (2ε _d =?U) is identical to the antiferromagnetic Kondo model. The method and the results suggest the construction of a “polaron” model which in the approximation used is equivalent to the Kondo model as well as the Anderson model. From this a new picture of the “Kondo effect” in terms of spin fluctuations is developed.     

Applying the stochastic parallel gradient algorithm in the auto alignment problem for the amplifier channel of the UFL-2M facility

The procedure of automatic alignment of the four-pass amplifier channel of a UFL-2M facility has been simulated numerically in the presence of aberrations in the optical path. The alignment procedure is based on the “marker” or “reference” method. The control elements are directed by the stochastic parallel gradient algorithm. The order of executing the automatic alignment is determined. The numerical simulation shows the possibility of positioning the beam at the exit from the channel with an accuracy of 1% of the pinhole size in the far field and of 0.1% of the beam aperture size in the near field. It was established that the centering accuracy of the alignment beam in inner pinholes in the presence of optical inhomogeneities in the amplifier channel can be worse than at the exit of the channel. The possibility of symmetrizing the picture of far-field markers has been considered in the case where the position of the optical axis of the channel is unknown.     

Definitions and control of the CEP and CEO

The definitions of the carrier to envelope phase (CEP) and carrier to envelope offset (CEO) arc reviewed. It is pointed out that a unique separation of the field of an ultrashort pulse in a “carrier” and “envelope” is not always possible for ultrashort pulses. Another definition is proposed for pulses of a few optical cycles, that is not dependent on the notion of “carrier” and “envelope.” The carrier to envelope offset (CEO) is a frequency, generally defined as the ratio of the change in CEP between pulses, to the pulse (temporal) spacing. It is shown that the CEO exists for trains of long pulses, for which the CEP cannot be measured. Methods of measuring the CEO of a mode-locked laser are proposed. It is shown that MQW have a locking tendency on the CEO of two pulse trains.     

低于再碰撞阈值下强激光场原子非序列双电离

在最近的实验和理论研究中,我们探讨了氩原子和氖原子在红外强激光场中低于再碰撞阈值的非序列双电离问题。在研究中,我们发现在非序列双电离过程中,氖原子的电子关联表现为在激光偏振面内肩并肩出射,而对于氩原子的电子关联行为表现为在激光偏振面内的背对背出射,我们采用三维半经典模型（考虑电子隧道电离）很好地解释了实验结果。在阈值附近,我们发现电子在激光场中的多次散射以及电子再碰撞激发后电子隧道电离是氩原子反关联行为的主要原因,而电子在激光场作用下的单次碰撞是电子关联行为的主要原因。通过测量双电离过程中产生电子的横向电子动量分布,观察到了库伦聚焦效应,我们认为这是非经典的关联行为。最后,我们给出了氩原子和氖原子在激光场中阈值的解析模型,并给出了原子的关联和反关联激光强度区域.     

激光对光学薄膜加热过程的数值分析

采用“交替隐型算法”对光学薄膜中的加热过程进行了数值分析,求解得到了薄膜中的二维温度场,并给出一些计算实便。     

Why optical data communications and why now?

Our focus here is on data communications within IT equipment and in IT data centers. Optical communications is not new. Thus the obvious question is likely; why a paper entitled, “Why optical data communications and why now?”. The reasons are twofold. First, optical data communications is more necessary now than it has ever been in the past. It is not excessive to even consider that it will be required in the not too distant future. Second, the advances in the broad field of photonics and optics have brought optical communications nearly to the point that it can finally cross over the threshold to be less expensive than electronic signaling. In this paper we make the case why we must aggressively pursue optics for data communications at all length scales within the data center. The summarization of this paper is that optical communications is inevitable, and we offer reasons why we believe this is true.     

Spatial and temporal coherence effects in interference microscopy and full‐field optical coherence tomography

Low‐coherence optical microscopy or optical coherence microscopy uses light with short coherence length. The well‐known case is: “white‐light interferometry”, which became recently more known as: “optical coherence tomography”. However, when lenses and microscope objectives are used to create interferometric images, in what is known classically as “interference microscopy” or today as “full‐field optical coherence tomography” the spatial coherence starts to play a critical role. In this article the coherence effects in low‐coherence optical microscopy are reviewed. As this technology is becoming increasingly publicized due to its importance in three‐dimensional imaging, particularly of scattering biological media and optical metrology, the understanding of the fundamental physics behind it is essential. The interplay between longitudinal spatial coherence and temporal coherence and the effects associated with them are discussed in detail particularly when high numerical apertures are used. An important conclusion of this study is that a high‐contrast, high‐resolution system for imaging of multilayered samples is the one that uses narrowband illumination and high‐NA objectives with an index‐matching fluid. Such a system, when combined with frequency‐domain operation, can reveal nearly real‐time three‐dimensional images, and is thus competitive with confocal microscopy.     

脉冲电场下两种电极材料表面电子发射阈值特性的实验研究

研究了金属表面电子发射阈值的测量原理.以待测材料为阴极,以法拉第筒作为阳极收集电子.在"晨光号"加速器上,测量了不同粗糙度的304L不锈钢和铝表面电子发射阈值及经表面涂覆工艺处理后这两种电极材料表面电子发射阈值.研究发现:电极表面磨光可以抑制电子发射,随着粗糙度的增加,电子发射阈值降低;金属表面涂覆对抑制电子发射效果更为显著,电子发射阈值增加了一倍.     

Dynamical theory of magnetic quantum beats of γ radiation passing through a thick <Superscript>181</Superscript>Ta Mössbauer absorber

The theory of transmission of magnetic quantum beats of γ radiation, induced by an RF magnetic field in the magnetic resonance method, is considered. The dependence of the γ-resonance spectra of harmonics on the “optical” path length and the polarization of the incident γ radiation is analyzed. It is shown that the dependence of the harmonic intensity on the “optical” path length is nonmonotonic. The polarization selection of harmonics and their spectral sensitivity are revealed.     

Charged particle motion in the field of a short laser pulse of relativistic intensity

The electron motion in the field of the laser radiation of relativistic intensity was analyzed using the Lorentz force. In the laser pulse field, an initially rest electron does not move along trajectories such as “figure eight”. At relativisitic intensities, the electron oscillations in an optical field are significantly anharmonic.     

Microwave diagnostics of the influence of physical effects on the electromagnetic characteristics of water

Changes in the dielectric constant and dielectric loss tangent of water that was first subjected to impact loads under the action of an alternating magnetic field were determined quantitatively using a micro-wave system, which allows solution of the inverse problem. The results of measurements of the optical spectrum of water in the “transmission” mode, which was subjected to a shock load, in comparison with the optical spectrum of distilled water, are described.     

Generalized derivation of equations for four-wave interaction in photorefractive media

The emergence of optical waves out of optical noise (fanning) in a photorefractive medium is considered in an unconventional manner, i.e., using the Lorentz lemma and ensemble averaging. The derivation of equations for four-wave interaction in the scheme of a double incoherent phase-conjugate mirror is described in detail. Numerical calculation based on the resulting system of equations provides insight into the effect of noise on the oscillation threshold and makes it possible to discover the “higher threshold” effect in saturation-free noisy materials.     

Variation of the grazing angular momentum with energy and deviations from the quarter-point recipe

The energy-dependence of the grazing angular momentum is given for a Saxon-Woods nuclear potential. Deviations from the “quarter-point recipe” are found and explained in terms of the optical model reflection coefficients and an optical model “deflection function”.     

Measurements of the laser linewidth due to quantum phase and quantum amplitude noise above and below threshold. I

The natural linewidths and line shapes due to quantum phase and quantum amplitude noise have been investigated above, within and below the threshold region of laser operation using a Fourier spectroscopic technique. Outside the threshold region the linewidths of the laser spectrum were found to be inversely proportional to the laser power, and measurements confirm the “factor of two” difference in the linewidth equation. Within the threshold region the results are in agreement with calculations of Hempstead, Lax and Risken. A Mach-Zehnder interferometer with optical path differences up to 1500 meters was used for the measurements. The method of investigation combines a high spectral resolution with a good signal-to-noise ratio. The method is suited to linewidth measurements of a laser both above and below threshold and allows the technical and natural linewidths to be clearly distinguished.     

无机纳米发光材料研究展望:如何走出自己的舒适区?

无机纳米发光材料由于其独特的发光性质,具有广泛的应用前景。本文结合作者的科研经历,展望了无机纳米发光材料未来的发展机遇和挑战,聚焦该领域前沿“痛点”和“冷门”,探讨研究工作如何面向国家重大需求。倡议科学家应走出自己的研究舒适区,树立自己的标签性工作,共同推进无机纳米发光材料研究的可持续发展。     

真空条件下激光诱导光纤损伤特性研究

实验研究并分析了调Q Nd:YAG 脉冲激光诱导光纤损伤特性.设计了在真空条件下全石英光纤传输1064 nm 脉冲激光实验.通过将激光注入光纤端面气压降低到10—100 Pa, 光纤端面击穿阈值提高到大气环境下的185 倍.结合光纤端面损伤形貌分析可知,光纤端面损伤主要是由于激光驻波场和烧蚀共同作用的结果,光纤端面或内部大量的缺陷降低了光纤抗激光损伤的能力.在真空条件下由于光纤端面光学击穿阈值的提高,激光诱导光纤损伤特性又表现出了另外一种损伤模式——光纤初始输入段损伤.它发生在光纤输入段附 关键词： 激光损伤 光束传输 真空 石英光纤     

Optical properties of LiNbO3:Mg(5.21 mol %) and LiNbO3:Fe(0.009 mol %):Mg(5.04 mol %) crystals

Using methods of electronic spectroscopy, laser conoscopy, photoinduced (photoreactive) light scattering, and Raman light-scattering spectroscopy, we have studied the optical homogeneity, optical transmission, and photorefractive properties of single crystals LiNbO₃:Mg(5.21 mol %) and LiNbO₃:Fe(0.009 mol %):Mg(5.04 mol %) that were grown from congruent melts. We have ascertained that doping with “nonphotorefractive” Mg²⁺ cations causes suppression of the photorefractive effect in a lithium-niobate crystal. Upon double doping (Fe:Mg), if the concentration of Mg²⁺ cations exceeds the threshold concentration, the photorefractive effect is almost not observed and the presence of “photorefractive” Fe cations does not affect the photorefractive effect as strongly as in congruent crystals doped with Fe.     

MATFESA: strain and refractive index field estimation after femtosecond laser interaction with transparent material

In this paper we present the development of an open code (“MATFESA”) based on the Finite Element Method (FEM) which can be used to estimate the strain and refractive index fields after femtosecond laser writing process by means of an iterative analysis. The fs-laser pulse residual stress control is the key to obtain high performance guiding structures for photonics. The whole complex physical problem consists in almost three steps inside the material during/after femtosecond laser interaction which cannot be analyzed using thermodynamic equilibrium equations. These are: ionization, expansion and re-solidification. In the numerical model solved, a mechanical expansion is introduced in the focal plane to simulate laser interaction at intensities above the optical breakdown threshold. Numerical results were compared to experimental measurements of optical guided modes in LiNbO₃ fs-waveguides. The MATFESA model was compared with ABAQUS commercial software in order to verify the strain field results and also to test the 2D, plane strain approximation.