Diffraction radiation interference pattern obtained upon electron beam propagation through a slit target

The interference pattern of coherent diffraction radiation (CDR) from a silt target is measured using the extracted beam of the microtron at Tomsk Polytechnic University. A theoretical interference pattern is calculated based on a model developed earlier for calculating the CDR characteristics in the far and near zones with allowance for the detector-sensitivity function. Comparison of the theoretical and experimental interference patterns makes it possible to obtain information about the longitudinal size of the bunch. The results obtained by the proposed and earlier methods agree well with each other.     

高斯光束照射下与矩孔相关的孔径衍射

依据基尔霍夫衍射理论,利用幂级数展开的方法,推导出傍轴条件下高斯光束的矩孔及单缝衍射的近似计算公式,并通过数值计算、数值模拟等方法对衍射场的基本特性进行了讨论。     

带有相位拓朴数的环形相位板调控高斯光束的梯度力

 用基于德拜近似条件的矢量衍射理论研究了带有相位拓朴数的环形相位板调控高斯光束的光梯度力分布,改变相位板环形区的相对半径或当相位板的相位以一定拓扑数呈现拓扑变化时,可以调节光学系统焦点区域的光梯度力分布,形成各种非常有规则的几何形状的光陷阱,如当拓朴数分别取3,4,5,6时,可形成三角形、四边形、五边形和六边形光陷阱。此种相位板可用来构建可调的光镊系统,且通过调节相位板的各区域半径和拓扑数可以得到所希望的光陷阱。     

带有相位拓朴数的环形相位板调控高斯光束的梯度力

用基于德拜近似条件的矢量衍射理论研究了带有相位拓朴数的环形相位板调控高斯光束的光梯度力分布,改变相位板环形区的相对半径或当相位板的相位以一定拓扑数呈现拓扑变化时,可以调节光学系统焦点区域的光梯度力分布,形成各种非常有规则的几何形状的光陷阱,如当拓朴数分别取3,4,5,6时,可形成三角形、四边形、五边形和六边形光陷阱。此种相位板可用来构建可调的光镊系统,且通过调节相位板的各区域半径和拓扑数可以得到所希望的光陷阱。     

Diffraction of millimeter waves by projecting a shadow pattern onto a semiconductor

The transmission of millimeter waves through a semiconductor changes according to the amount of light falling on it. In the experiments reported here, a pattern of light and shadow is projected onto a sheet of semiconductor and the regions of greater and lesser transmission serve as a diffracting object for a millimeter-wave beam. The light source is a quartz tungsten halogen lamp. A lock-in amplifier is employed to overcome difficulties due to the differences in transmitted power being small.     

Total internal reflection of a Gaussian light beam

An approximate theoretical model for calculating the reflected and refracted fields of a Gaussian light beam at a plane interface between two isotropic media is formulated on the basis of a Fourier integral. In the vicinity of the critical angle of incidence (for total internal reflection) the model predicts the presence of two refracted beams, one displaced along the interface by an amount equal to the Goos-Hänchen shift; curvature of the phase fronts and nonalignment of the effective directions of energy and phase propagation occur for each beam, as in an anisotropic medium.     

Radiation forces of a dielectric medium plate induced by a Gaussian beam

Based on the angular spectrum method, we investigate the radiation forces on a finite-size dielectric medium plate induced by a Gaussian beam. The formulas for the radiation force along longitudinal and transverse direction are derived, and numerically calculation is performed. It is shown that for the finite-size dielectric medium plate, the radiation forces exerted by the Gaussian beam is dependent upon the angle and position of a single ray striking on the plate and the intensity of light. Our numerical results indicate that if we choose the appropriate parameters there will be enough transverse forces to overcome the gravity force, making the plate move upwards.     

Gradient force evolution of Gaussian beam induced by a phase plate

The evolution of gradient force pattern induced by an annular phase distribution plate is numerically investigated in this paper. The phase plate, which may alter the wavefront phase of incident Gaussian beam with tunable topological charge, consists of two concentric portions, one center circle portion and one annular portion. Numerical simulations show that the proposed plate can induce the tunable gradient force on the particles in the focal region. By adjusting the geometrical parameters or changing the topological charge of the phase-shifting plate, some novel trap patterns may occur, such as triangle shape trap, quadrangle shape trap, pentagon shape trap, hexagon shape trap, and the shapes of optical traps change very considerably. Therefore, the phase plate may be very advantageous for constructing tunable optical traps. The method is more versatile in that it allows precise control of the parameters and has the possibility of generating specific patterns of optical vortices. The gradient force pattern focal of intensity distribution depends on both the annular width and the topological charge.     

Focusing properties of Gaussian beam by a nonspiral phase plate system

In this article, a nonspiral plate is investigated numerically by vector diffraction theory to observe the focusing properties of Gaussian beams. Both low- and high-numerical-aperture (NA) optical systems are considered in the investigation. It is found that the parameter of NA and the phase vary rate of the phase plate influence the focal intensity distribution considerably. When a nonspiral plate is used to provide linear phase variation on one half of the Gaussian beam, it may adjust the focal spot considerably and conveniently. Changing the vary rate of the phase plate or the parameter of NA can alter optical intensity distribution; some novel focal spots and focal switch may also occur.     

Transformation of a Gaussian light beam reflected in the vicinity of the Brewster angle

Variations in the profile and shift of a Gaussian light beam upon reflection from a plane interface between a transparent dielectric and a medium with a complex refractive index are studied. The beam is assumed to be incident at angles close to the Brewster’s angle, where the effects of transformation of the beam profile are most substantial. Based on numerical analysis, the reflected beam profiles are obtained for different properties of the media, parameters of the incident beam, and positions of the plane of observation.     

会聚高斯光束焦点附近的三维光分布状态

根据惠更斯 菲涅耳原理 ,推导出了会聚高斯光束经圆形孔径衍射后焦点附近的三维光分布状态级数表达式 ,并与经典的均匀光波理论进行了比较。讨论了会聚高斯光束焦移与光学系统及高斯光束参数的关系。给出了会聚高斯光束焦点附近的等照度线图。结果表明 ,对于大菲涅耳数系统来说 ,其光强分布具有对称性     

Second-order temporal interference of two independent light beams at an asymmetrical beam splitter

The second-order temporal interference of classical and nonclassical light at an asymmetrical beam splitter is discussed based on two-photon interference in Feynman's path integral theory. The visibility of the second-order interference pattern is determined by the properties of the superposed light beams, the ratio between the intensities of these two light beams, and the reflectivity of the asymmetrical beam splitter. Some requirements about the asymmetrical beam splitter have to be satisfied in order to ensure that the visibility of the second-order interference pattern of nonclassical light beams exceeds the classical limit. The visibility of the second-order interference pattern of photons emitted by two independent single-photon sources is independent of the ratio between the intensities. These conclusions are important for the researches and applications in quantum optics and quantum information when an asymmetrical beam splitter is employed.     

Transformation and shift of a Gaussian light beam upon reflection from a resonant medium

The specific features of the transformation and shift of a Gaussian beam reflected from a resonant absorbing medium are analyzed numerically. The study is based on the expansion of the field of the incident Gaussian beam into plane-wave components by using the Fourier integral transform. The calculations are performed for a frequency range covering the resonance region. The conditions for the splitting of the profile of the reflected beam and for its negative shift are established.     

Interference pattern generation and simulation in the single beam of a white light continuum

We demonstrate the interference phenomenon in the White Light Continuum(WLC) generated by a single femtosecond laser beam. Different kinds of spatial interference patterns of the WLC generation under various conditions were investigated. The spatial patterns were attributed to interference between the filaments in the WLC generated by the fundamental laser beam yielding the diffraction effect from spatial confinement. Simulations of different patterns were performed. By comparing the results of simulation with those of experiments,the distances of several micrometers between the neighboring filaments can be derived,which agree with the literature values from direct measurements.     

Investigation of diffractive optical element for shaping a Gaussian beam into a ring-shaped pattern

To convert a given single-mode He–Ne laser beam into a ring-shaped intensity distribution, a diffractive optical element with 16 levels was designed by YG amplitude-phase retrieval and iteration algorithm. This beam shaper is investigated experimentally and compared with the results of the computer design. The results show good conformity, and the measured diffraction efficiency is 87.2%. In addition, the diffractive effect is observed when the distance between diffractive optical element and CCD is changed.