Search results for "Physics::Optics"

Laser-assisted narrow gap arc welding of an 18MND5 steel thick plate

2020

Abstract Narrow gap arc welding is a common solution for the welding of thick structures. In this study, a defocused laser beam is used to pre-melt the narrow gap walls in front of an arc-welding bath. Such a welding configuration can be referred to a hybrid welding configuration. In the present work, a particular attention is given to evaluation of the interaction between an arc plasma and a defocused laser beam. High-speed imaging of the metal transfer through arc plasma is achieved thanks to a diode laser illumination system. Electrical arc parameters are logged, synchronously, in order to perform a correlation analysis and to make a diagnosis of the interaction level between laser beam …

Generalized Thru-Reflect-Line Calibration Technique for the Measurement of Multimodal Radiating Waveguides

2017

The objective of this letter is to extend the use of the generalized thru-reflect-line measurement technique to the case of a radiating multimodal rectangular waveguide aperture. Although this radiating aperture has been carefully studied from a theoretical point of view, the relevant experimental characterization has been limited to the case where the feeding waveguide is monomodal. In addition to theory, we also present experimental results that agree quite well with full-wave simulations, thereby fully validating the measurement technique.

Out-of-plane orientation of luminescent excitons in two-dimensional indium selenide.

2019

Van der Waals materials offer a wide range of atomic layers with unique properties that can be easily combined to engineer novel electronic and photonic devices. A missing ingredient of the van der Waals platform is a two-dimensional crystal with naturally occurring out-of-plane luminescent dipole orientation. Here we measure the far-field photoluminescence intensity distribution of bulk InSe and two-dimensional InSe, WSe2 and MoSe2. We demonstrate, with the support of ab-initio calculations, that layered InSe flakes sustain luminescent excitons with an intrinsic out-of-plane orientation, in contrast with the in-plane orientation of dipoles we find in two-dimensional WSe2 and MoSe2 at room-…

2017

Significant progress in nonlinear and ultrafast optics has recently opened new and exciting opportunities for terahertz (THz) science and technology, which require the development of reliable THz sources, detectors, and supporting devices. In this work, we demonstrate the first solid-state technique for the coherent detection of ultra-broadband THz pulses (0.1–10 THz), relying on the electric-field-induced second-harmonic generation in a thin layer of ultraviolet fused silica. The proposed CMOS-compatible devices, which can be realized with standard microfabrication techniques, allow us to perform ultra-broadband detection with a high dynamic range by employing probe laser powers and bias v…

Large area conductive nanoaperture arrays with strong optical resonances and spectrally flat terahertz transmission

2017

Using simple and inexpensive nanosphere lithography, we produce large, centimeter-squared sized thin golden films patterned with a hexagonal array of nanoapertures with controllable dimensions on the order of 100–300 nm, spaced by a 350–375 nm pitch distance. The optical transmission spectra of our samples are dominated by the resonant plasmonic features in the spectral range 500–700 nm, caused by the nanostructure in the film. At the same time, the transmission at terahertz (THz) radiation is as high as ∼10% and is spectrally flat. Our measurements are in agreement with finite difference time domain simulations. Such thin metal hole array films allow for very efficient injection of optical…

Studies towards a directional polychromatic sodium laser guide star

2018

In this work we discuss a mechanism for generation of a coherent source of light from the mesosphere as a new concept of directional laser guide star. In contrast to the near-isotropic spontaneous emission, nonlinear processes in atomic vapors like amplified spontaneous emission can yield highly directional emission in the forward and backward directions. Along with directional emission, excited sodium atoms also radiate at different wavelength creating a polychromatic laser guide star (PLGS). If feasible, a directional PLGS would provide a net gain in the return flux of several orders of magnitude compared to traditional LGS schemes, making possible laser-guided tip/tilt-correction in adap…

Parametrical Optomechanical Oscillations in PhoXonic Whispering Gallery Mode Resonators

2019

AbstractWe report on the experimental and theoretical analysis of parametrical optomechanical oscillations in hollow spherical phoxonic whispering gallery mode resonators due to radiation pressure. The optically excited acoustic eigenmodes of the phoxonic cavity oscillate regeneratively leading to parametric oscillation instabilities.

Nanoscale strain-engineering and optics of quantum emitters in a two-dimensional semiconductor

2017

We present deterministic fabrication of a two-dimensional lattice of quantum emitters in an atomically thin semiconductor. Resonant laser spectroscopy of these emitters reveals localized exciton states that exhibit stable, bright and high-purity single photon emission.

Observation of elastic anisotropy in strained optical nanofibers using Brillouin spectroscopy

2019

Optical nanofibers (ONFs) are excellent nanophotonic platforms for many applications such as optical sensing, quantum photonics, and nonlinear optics, due to both tight optical confinement and their evanescent field. From an acoustic viewpoint, it has recently been reported the observation of a new class of Brillouin acoustic resonances in optical nanofibers, including hybrid shear/longitudinal acoustic waves (HAWs) and surface acoustic waves (SAWs) [1–2]. It has been later shown that, under axial tensile strain, the Brillouin frequency shifts (BFS) of these elastic resonances are fundamentally different from that of standard optical fibers [3]. This is principally due to the hybrid nature …

Nonlinear femtosecond pulse propagation in an all-solid photonic bandgap fiber

2009

Nonlinear femtosecond pulse propagation in an all-solid photonic bandgap fiber is experimentally and numerically investigated. Guiding light in such fiber occurs via two mechanisms: photonic bandgap in the central silica core or total internal reflection in the germanium doped inclusions. By properly combining spectral filtering, dispersion tailoring and pump coupling into the fiber modes, we experimentally demonstrate efficient supercontinuum generation with controllable spectral bandwidth.