Growth Angle and Melt Meniscus of the RF-heated Floating Zone in Silicon Crystal Growth

This article presents a direct measurement of the growth angle during the growth of a cylindrical 2" silicon crystal using a radio-frequency heated floating zone process. From the high-resolution pictures taken during the process, this growth angle was evaluated to be 11{\deg}{\pm}2{\deg}. Furthermore, the free surface of the melt was modeled using the Laplace-Young equation. This model has to include the electromagnetic pressure calculated by the surface ring currents approximation. The results were compared to the experimental free surface derived from video frames. It could be shown that the calculated free surface will only fit the experimentally determined one if the right growth angle is considered

Face tracking using a hyperbolic catadioptric omnidirectional system

In the first part of this paper, we present a brief review on catadioptric omnidirectional systems. The special case of the hyperbolic omnidirectional system is analysed in depth. The literature shows that a hyperboloidal mirror has two clear advantages over alternative geometries. Firstly, a hyperboloidal mirror has a single projection centre [1]. Secondly, the image resolution is uniformly distributed along the mirror’s radius [2]. In the second part of this paper we show empirical results for the detection and tracking of faces from the omnidirectional images using Viola-Jones method. Both panoramic and perspective projections, extracted from the omnidirectional image, were used for that purpose. The omnidirectional image size was 480x480 pixels, in greyscale. The tracking method used regions of interest (ROIs) set as the result of the detections of faces from a panoramic projection of the image. In order to avoid losing or duplicating detections, the panoramic projection was extended horizontally. Duplications were eliminated based on the ROIs established by previous detections. After a confirmed detection, faces were tracked from perspective projections (which are called virtual cameras), each one associated with a particular face. The zoom, pan and tilt of each virtual camera was determined by the ROIs previously computed on the panoramic image. The results show that, when using a careful combination of the two projections, good frame rates can be achieved in the task of tracking faces reliably

Laser calibration system for the CERES Time Projection Chamber

A Nd:YAG laser was used to simulate charged particle tracks at known positions in the CERES Time Projection Chamber at the CERN SPS. The system was primarily developed to study the response of the readout electronics and to calibrate the electron drift velocity. Further applications were the determination of the gating grid transparency, the chamber position calibration, and long-term monitoring of drift properties of the gas in the detector.Comment: 28 pages, 26 figures; reference to the TPC preprint update

An investigation of film wavy structure in annular flow using two simultaneous LIF approaches

The paper is devoted to development and validation of film thickness measurement techniques in interfacial gas-liquid flows. The specific flow investigated here is that of downwards (co-flowing) annular flow in a vertical pipe, however, many of the observations and findings are transferable to similar flow geometries. Two advanced spatially resolved techniques, namely planar laser-induced fluorescence and brightness-based laser-induced fluorescence , are used simultaneously in the same area of interrogation. A single laser sheet is used to excite fluorescence along one longitudinal section of the pipe, and two cameras (one for each method) are placed at different angles to the plane of the laser sheet in order to independently recover the shape of the interface along this section. This allows us to perform a cross-validation of the two techniques and to analyse their respective characteristics, advantages and shortcomings

Complete polarization control for a nanofiber waveguide using directional coupling

Optical nanofiber waveguides are widely used for near-field delivery and measurement of light. Despite their versatility and efficiency, nanofibers have a critical drawback - their inability to maintain light's polarization state on propagation. Here, we design a directional coupler consisting of two crossed nanofibers to probe the polarization state at the waist region. Directionality of coupling occurs due to asymmetric dipolar emission or spin-locking when the evanescent field pattern breaks the mirror symmetry of the crossed-nanofiber system. We demonstrate that, by monitoring the outputs from the directional coupler, two non-orthogonal polarization states can be prepared at the nanofiber waist with a fidelity higher than 99%. Based on these states, we devise a simple and reliable method for complete control of the polarization along a nanofiber waveguide.Comment: 8 pages, 8 figure

Light-sheet microscopy: a tutorial

This paper is intended to give a comprehensive review of light-sheet (LS) microscopy from an optics perspective. As such, emphasis is placed on the advantages that LS microscope configurations present, given the degree of freedom gained by uncoupling the excitation and detection arms. The new imaging properties are first highlighted in terms of optical parameters and how these have enabled several biomedical applications. Then, the basics are presented for understanding how a LS microscope works. This is followed by a presentation of a tutorial for LS microscope designs, each working at different resolutions and for different applications. Then, based on a numerical Fourier analysis and given the multiple possibilities for generating the LS in the microscope (using Gaussian, Bessel, and Airy beams in the linear and nonlinear regimes), a systematic comparison of their optical performance is presented. Finally, based on advances in optics and photonics, the novel optical implementations possible in a LS microscope are highlighted.Peer ReviewedPostprint (published version