Single-Pixel Imaging with Heralded Single Photons

Traditional remote sensing applications are often based on pulsed laser illumination with a narrow linewidth and characteristic repetition rate, which are not conducive to covert operation. Whatever methods are employed for covert sensing, a key requirement is for the probe light to be indistinguishable from background illumination. We present a method to perform single-pixel imaging that suppresses the effect of background light and hence improves the signal-to-noise ratio by using correlated photon-pairs produced via spontaneous parametric down conversion. One of the photons in the pair is used to illuminate the object whilst the other acts as a temporal reference, allowing the signal photons to be distinguished from background noise. This heralding method shows how the noise regime is key to producing higher contrast images.

Observation of frequency dependent resonances in magnetic vortex core gyration using time-resolved magneto-optical Kerr microscope with pulsed semiconductor laser illumination

Frequency dependent resonance of magnetic vortex core gyration in micrometer sized permalloy squares was observed by time-resolved magneto-optical Kerr microscope using pulsed semiconductor lasers as a light source in stroboscopic method. Uniform and efficient laser illumination was realized by a speckle reducer consisting of an oscillating multimode optical fiber and a microbending mode scrambler. The resonance frequency of the same sized permalloy squares showed a non-uniformity of up to 15%, suggesting the flatness of the underlayer have a strong influence to the gyration motion.

Normalization in dynamic speckle analysis for non-destructive monitoring of speed of processes

The paper is dedicated to analysis of normalized intensity-based pointwise algorithms for processing dynamic speckle images with spatially varying speckle statistics in non-destructive visualization of regions of faster or slower changes across an object. Both existing and newly proposed algorithms are analyzed. Extraction of speed of changes is done by acquiring correlated in time speckle images formed on the object surface under laser illumination. The studied algorithms have been applied to simulated low and high contrast speckle data. Their performance has been compared to processing of binary patterns as another approach for dealing with varying speckle statistics in the acquired images. The efficiency of the algorithms have been checked on the experimental data, including data in a compressed format. We have proven that the algorithms with normalization at successive instants by a sum of two intensities or a single intensity outperform as a whole the algorithms which apply the time-averaged estimates of the mean value and the variance of speckle intensity.

Anomalous anti-Stokes Scattering in Amorphous Carbon Thin Films

This work is devoted to a study of temperature-dependent Raman scattering of amorphous carbon (a-C) thin films. An anomalous rise of the anti-Stokes intensity in respect to the Stokes intensity was observed. This result comes from the resonant enhancement of anti-Stokes scattering of defects of graphite-like crystals. The observed discrepancy is quantified through a coefficient, a, defined as a ratio of the anti-Stokes and Stokes scattering cross sections. Understanding the mechanism for anomalous enhancement of anti-Stokes scattering provides a way for correct probing the temperature of the a-C thin films exposed to cw laser illumination.

Optical Heating Controlled With a Thermoplasmonic Metasurface

We develop a photothermal technology to control optical heating of polymer and liquid crystal films through a refractory titanium nitride (TiN) metasurface. The metasurface represents an array of identical square-shaped TiN nanoantennas on a Si substrate. Upon CW laser illumination, a TiN nanoantenna experiences anomalous Joule heating at a plasmon resonance. A temperature rise provides a unique opportunity for locally probing phase transitions. In the case of heterogeneous PMMA thin films or polymeric blends, a controlled optical heating is needed to probe the glass transition temperature (Tg) of their constituents. Here, we model a controlled thermal response originating from the TiN nanoantenna under CW laser illumination by using FDTD/FEM methods.

Picosecond Pulsed Laser Illumination: An Ultimate Solution for Photonic vs. Thermal Processes’ Contest in SOI Photo- Activated Modulator

The functionality of a nanoscale silicon-based optoelectronic modulator is deeply analyzed while it appears that two competing processes, thermal and photonic, are occurring at the same time, and are preventing the optimization of the electro-optics coupling. While an incident illumination-beam first process is translated into photons, generating pairs of electrons-holes, a second process of thermal generation, creating phonons enables a loss of energy. Complementary studies, combining strong analytical models and numerical simulations, enabled to better understand this competition between photonic and thermal activities, in order to optimize the modulator. Moreover, in order to prevent unnecessary heating effects and to present a proposed solution, a picosecond pulsed laser is suggested and demonstrated as the ultimate solution so no energy will be wasted in heat, and still the photonic energy will be fully used. First ever-analytical solution to the heating produced due to the laser illumination applied on a nano-photonic device, while the illumination is produced in a periodic time changing function, e.g. a pulsed illumination, is presented. The present case study and proposed adapted solution can serve as a basis of generic approach in sensors’ activation towards optimized photonics absorption.