Dynamic visual cryptography scheme on the surface of a vibrating structure

Dynamic visual cryptography scheme based on time-averaged fringes generated by Ronchi-type geometric moiré gratings on finite element grids is proposed in this paper. A single cover image is used to encode the secret image and is formed on the surface of a deformable structure. Time-averaged moiré fringes leak the secret when the structure is oscillated according to a predefined Eigen-shape. The envelope functions determining the motion induced blur of the Ronchi-type moiré grating depend on the characteristic features of the motion. And though harmonic oscillations do not result into a completely uniform time-averaged image of the Ronchi-moiré grating, initial phase scrambling and phase normalization algorithms are used to encode the secret in the cover image. Theoretical relationships between the amplitude of the Eigen-shape, the order of the not completely developed time-averaged fringe and the pitch of the deformable one-dimensional Ronchi-type moiré grating are derived

COMPRESSIVE IMAGING AND DUAL MOIRE´ LASER INTERFEROMETER AS METROLOGY TOOLS

Metrology is the science of measurement and deals with measuring different physical aspects of objects. In this research the focus has been on two basic problems that metrologists encounter. The first problem is the trade-off between the range of measurement and the corresponding resolution; measurement of physical parameters of a large object or scene accompanies by losing detailed information about small regions of the object. Indeed, instruments and techniques that perform coarse measurements are different from those that make fine measurements. This problem persists in the field of surface metrology, which deals with accurate measurement and detailed analysis of surfaces. For example, laser interferometry is used for fine measurement (in nanometer scale) while to measure the form of in object, which lies in the field of coarse measurement, a different technique like moire technique is used. We introduced a new technique to combine measurement from instruments with better resolution and smaller measurement range with those with coarser resolution and larger measurement range. We first measure the form of the object with coarse measurement techniques and then make some fine measurement for features in regions of interest. The second problem is the measurement conditions that lead to difficulties in measurement. These conditions include low light condition, large range of intensity variation, hyperspectral measurement, etc. Under low light condition there is not enough light for detector to detect light from object, which results in poor measurements. Large range of intensity variation results in a measurement with some saturated regions on the camera as well as some dark regions. We use compressive sampling based imaging systems to address these problems. Single pixel compressive imaging uses a single detector instead of array of detectors and reconstructs a complete image after several measurements. In this research we examined compressive imaging for different applications including low light imaging, high dynamic range imaging and hyperspectral imaging

The Solar Particle Acceleration Radiation and Kinetics (SPARK) Mission Concept

© 2023by the authors. Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Particle acceleration is a fundamental process arising in many astrophysical objects, including active galactic nuclei, black holes, neutron stars, gamma-ray bursts, accretion disks, solar and stellar coronae, and planetary magnetospheres. Its ubiquity means energetic particles permeate the Universe and influence the conditions for the emergence and continuation of life. In our solar system, the Sun is the most energetic particle accelerator, and its proximity makes it a unique laboratory in which to explore astrophysical particle acceleration. However, despite its importance, the physics underlying solar particle acceleration remain poorly understood. The SPARK mission will reveal new discoveries about particle acceleration through a uniquely powerful and complete combination of γ-ray, X-ray, and EUV imaging and spectroscopy at high spectral, spatial, and temporal resolutions. SPARK’s instruments will provide a step change in observational capability, enabling fundamental breakthroughs in our understanding of solar particle acceleration and the phenomena associated with it, such as the evolution of solar eruptive events. By providing essential diagnostics of the processes that drive the onset and evolution of solar flares and coronal mass ejections, SPARK will elucidate the underlying physics of space weather events that can damage satellites and power grids, disrupt telecommunications and GPS navigation, and endanger astronauts in space. The prediction of such events and the mitigation of their potential impacts are crucial in protecting our terrestrial and space-based infrastructure.Peer reviewe

Metasurface Holographic Optical Traps for Ultracold Atoms

We propose metasurface holograms as a novel platform to generate optical trap arrays for cold atoms with high fidelity, efficiency, and thermal stability. We developed design and fabrication methodologies to create dielectric, phase-only metasurface holograms based on titanium dioxide. We experimentally demonstrated optical trap arrays of various geometries, including periodic and aperiodic configurations with dimensions ranging from 1D to 3D and the number of trap sites up to a few hundred. We characterized the performance of the holographic metasurfaces in terms of the positioning accuracy, size and intensity uniformity of the generated traps, and power handling capability of the dielectric metasurfaces. Our proposed platform has great potential for enabling fundamental studies of quantum many-body physics, and quantum simulation and computation tasks. The compact form factor, passive nature, good power handling capability, and scalability of generating high-quality, large-scale arrays also make the metasurface platform uniquely suitable for realizing field-deployable devices and systems based on cold atoms

Optical Fiber Interferometric Sensors

The contributions presented in this book series portray the advances of the research in the field of interferometric photonic technology and its novel applications. The wide scope explored by the range of different contributions intends to provide a synopsis of the current research trends and the state of the art in this field, covering recent technological improvements, new production methodologies and emerging applications, for researchers coming from different fields of science and industry. The manuscripts published in the Special issue, and re-printed in this book series, report on topics that range from interferometric sensors for thickness and dynamic displacement measurement, up to pulse wave and spirometry applications

Fast SLM-based linear and nonlinear structured illumination microscopy

Fluorescent microscopy becomes an essential tool for medical and biological investigations due to its major advantages of allowing for minimally invasive observation and rapid optical imaging. It is also a highly desirable tool to study the three dimensional interior of living specimens at a small scale. However, the resolution of optical systems is fundamentally limited by the diffraction of light, which consequently coins the development of super-resolution imaging methods. Structured illumination microscopy (SIM) is one of the super-resolution techniques. SIM provides a two-fold lateral resolution improvement for those types of samples where the fluorescence emission intensity depends linearly on the intensity of the illumination pattern. The concept of SIM is based on the Moiré effect. A structured illumination pattern is projected into the sample and high spatial frequency components of the biological sample, which are normally above the cut-off frequency of the optical transfer function and therefore lost, are then down-modulated to low spatial frequencies that reside inside the passband of the optical transfer function of the microscope. Typically, a lateral resolution of 100 nm becomes achievable in SIM. SIM is a wide-field technique and thus allows fast acquisition of large fields of view. This work discusses methods to improve the acquisition speed of SIM and to further enhance the resolution beyond the usual factor of two using nonlinear SIM (NL-SIM). Improvement of the acquisition speed is achieved by exploiting the advantages of a ferroelectric spatial light modulator (SLM) which offers fast switching of the illumination pattern, a modern sCMOS camera which provides fast readout and a novel synchronization approach between the different opto-electronical components