Self-Focusing Property of Partially Coherent Beam With Non-Uniform Correlation Structure in Non-Linear Media

Coherence in a light beam has the potential to serve as a degree of freedom for manipulating the beam. In this work, the self-focusing property of a partially coherent beam with a non-uniform correlation structure propagating in a non-linear medium is investigated. The analysis of the evolution of beam width reveals that the coherence structure plays a vital role in the self-focusing formation. A threshold condition for the coherence radius is proposed for the first time, and the relation of self-focusing length and initial coherence radius is studied numerically and analytically. It is shown that a feasible approach for manipulating the self-focusing length by adjusting the initial coherence radius is achieved.

An Alternative Operation Scheme to Improve the Efficiency of a Stark Decelerator

A Stark decelerator can slow down polar molecules to very low velocities. When the velocities are very low, the number of cold molecules obtained is very small. In order to obtain a higher quantity of cold molecules, inspired by the work of Reens et al. [Phys. Rev. Res. 2 (2020) 033 095], we propose an alternative method of operating a Stark decelerator. Through the trajectory simulation of OH molecules in the decelerator, we find that the number of cold molecules can be greatly increased by one order of magnitude at both low and high final velocities on a Stark decelerator consisting of around 150 electrodes. This development is due to the improved longitudinal and the transverse focusing property provided by the new switching schemes and the high-voltage configurations on the decelerator unit.

A solution to the complement of the generalized Luneburg lens problem

Lenses are of interest for the design of directive antennas and multi-optics instruments in the microwave, terahertz and optical domains. Here, we introduce an optical problem defined as the complement of the well-known generalized Luneburg lens problem. The spherically symmetric inhomogeneous lenses obtained as solutions of this problem transform a given sphere in the homogeneous region outside of the lens into a virtual conjugate sphere, forming a virtual image from a real source. An analytical solution is proposed for the equivalent geodesic lens using the analogy between classical mechanics and geometrical optics. The refractive index profile of the corresponding inhomogeneous lens is then obtained using transformation optics. The focusing properties of this family of lenses are validated using ray-tracing models, further corroborated with full-wave simulations. The numerical results agree well with the predictions over the analyzed frequency bandwidth (10–30 GHz). This virtual focusing property may further benefit from recent developments in the fields of metamaterials and transformation optics.

Self-Focusing of High-Power Laser Beam Through Cold Uniform Magnetized Plasma

In present paper the determination of the spot size of an ultra-short laser beam in uniform magnetized plasma with a dominant cold plasma has been studied. The liner dispersion relation of the laser beam propagating in Magnetized plasma have been found. Magnetic field is set up and source dependent expansion method is applied to determining the spot size of the intense laser beam with gaussian profile. The transverse magnetization of plasma and its impact on the self-focusing property of the dense laser governing to reduction in critical power necessary to self-focusing beam is shown.

Metrology of a Focusing Capillary Using Optical Ptychography

The focusing property of an ellipsoidal monocapillary has been characterized using the ptychography method with a 405 nm laser beam. The recovered wavefront gives a 12.5×10.4μm2 focus. The reconstructed phase profile of the focused beam can be used to estimate the height error of the capillary surface. The obtained height error shows a Gaussian distribution with a standard deviation of 1.3 μm. This approach can be used as a quantitative tool for evaluating the inner functional surfaces of reflective optics, complementary to conventional metrology methods.

Calculation on 2 cm ECRIT Thrust Regulation Based on 3D PIC Numerical Simulation Method

Drag-free control is the key technology for space gravitational wave detection, which will be completed by miniature thruster. 2 cm Electron Cyclotron Resonance Ion Thruster (ECRIT) may be used for the drag-free control. Therefore, the 3D PIC method is used to estimate the thrust regulation of 2 cm ECRIT through simulating the property of ion extracting from the double-grid system. Through analyzing the thrust performance and grid focusing property under different grid apertures, the better grid structure is selected for the subsequent calculation. On this basis, the influence of grid voltage and the ion density on the performance of the thruster is analyzed. The result shows that reducing grid aperture can reduce the thrust, but it also affects the focusing property of the grid. Changing the ion density can adjust the thrust in a wide range. At given grid structure and ion density, there is a suitable grid accelerating voltage range to ensure the best ion focus characteristics. Considering the thrust performance and focusing characteristics, the grid structure with screen and accelerating grid aperture in 0.6 mm and 0.34 mm is selected. When the ion density is 1×1 017, 0.7×1 017, 0.4×1 017 and 0.2×1 017 m-3, the thrust can range from 5.05 to 141.44 μN through adjusting the grid accelerating voltage. This study can provide information for analyzing the possibility of the thruster application.

New complex-valued activation functions

We present a new type of activation functions for a complex-valued neuralnetwork (CVNN). A proposed activation function is constructed such that itfixes a given ellipse. We obtain an application to a complex-valued Hopfieldneural network (CVHNN) using a special form of the introduced complexfunctions as an activation function. Considering the interesting geometricproperties of the plane curve ellipse such as focusing property, weemphasize that these properties may have possible applications in variousneural networks.