Search results for "Physics::Optics"
showing 10 items of 1958 documents
Efficient analysis of cubic junction of rectangular waveguides using admittance-matrix representation
2000
In the paper an efficient and accurate method, based on the multimode-admittance-matrix representation and the theory of cavities, is proposed for the analysis of a six-port ‘cubic’ junction composed of the orthogonal intersection of three rectangular waveguides. Very simple closed-form analytical expressions are explicitly detailed for all matrix elements of this basic key building block. More general waveguide multiport junctions, composed of a central cubic junction with arbitrarily shaped waveguide access ports, are also studied using a segmentation procedure. To validate the theory, numerical results are first discussed for a standard rectangular waveguide six-port cross junction. Fina…
Multi-level optimization of a fiber transmission system via nonlinearity management
2006
Nonlinearity management is explored as a complete tool to obtain maximum transmission reach in a WDM fiber transmission system, making it possible to optimize multiple system parameters, including optimal dispersion pre-compensation, with fast simulations based on the continuous-wave approximation. © 2006 Optical Society of America.
Programmable linear quantum networks with a multimode fibre
2019
Reconfigurable quantum circuits are fundamental building blocks for the implementation of scalable quantum technologies. Their implementation has been pursued in linear optics through the engineering of sophisticated interferometers. While such optical networks have been successful in demonstrating the control of small-scale quantum circuits, scaling up to larger dimensions poses significant challenges. Here, we demonstrate a potentially scalable route towards reconfigurable optical networks based on the use of a multimode fibre and advanced wavefront-shaping techniques. We program networks involving spatial and polarisation modes of the fibre and experimentally validate the accuracy and ro…
Laser-induced torques in metallic antiferromagnets
2021
We study the laser-induced torques in the antiferromagnet (AFM) Mn$_2$Au. We find that even linearly polarized light may induce laser-induced torques in Mn$_2$Au, i.e., the light does not have to be circularly polarized. The laser-induced torques in Mn$_2$Au are comparable in magnitude to those in the ferromagnets Fe, Co and FePt at optical frequencies. We also compute the laser-induced torques at terahertz (THz) frequencies and compare them to the spin-orbit torques (SOTs) excited by THz laser-pulses. We find the SOTs to be dominant at THz frequencies for the laser-field strengths used in experiments. Additionally, we show that the matrix elements of the spin-orbit interaction (SOI) can be…
Stability of E' centers induced by 4.7eV laser radiation in SiO2
2007
The kinetics of E' centers (silicon dangling bonds) induced by 4.7eV pulsed laser irradiation in dry fused silica was investigated by in situ optical absorption spectroscopy. The stability of the defects, conditioned by reaction with mobile hydrogen of radiolytic origin, is discussed and compared to results of similar experiments performed on wet fused silica. A portion of E' and hydrogen are most likely generated by laser-induced breaking of Si-H precursors, while an additional fraction of the paramagnetic centers arise from another formation mechanism. Both typologies of E' participate to the reaction with H_2 leading to the post-irradiation decay of the defects. This annealing process is…
Optical and dielectric properties of MoO 3 nanosheets for van der Waals heterostructures
2021
Two-dimensional (2D) insulators are a key element in the design and fabrication of van der Waals heterostructures. They are vital as transparent dielectric spacers whose thickness can influence both the photonic, electronic, and optoelectronic properties of 2D devices. Simultaneously, they provide protection of the active layers in the heterostructure. For these critical roles, hexagonal Boron Nitride (hBN) is the dominant choice due to its large bandgap, atomic flatness, low defect density, and encapsulation properties. However, the broad catalogue of 2D insulators offers exciting opportunities to replace hBN in certain applications that require transparent thin layers with additional opti…
Faster chiral versus collinear magnetic order recovery after optical excitation revealed by femtosecond XUV scattering
2020
While chiral spin structures stabilized by Dzyaloshinskii-Moriya interaction (DMI) are candidates as novel information carriers, their dynamics on the fs-ps timescale is little known. Since with the bulk Heisenberg exchange and the interfacial DMI two distinct exchange mechanisms are at play, the ultra-fast dynamics of the chiral order needs to be ascertained and compared to the dynamics of the conventional collinear order. Using an XUV free-electron laser we determine the fs-ps temporal evolution of the chiral order in domain walls in a magnetic thin film sample by an IR pump - X-ray magnetic scattering probe experiment. Upon demagnetisation we observe that the dichroic (CL-CR) signal conn…
Twisting graphene nanoribbons into carbon nanotubes
2011
Although carbon nanotubes consist of honeycomb carbon, they have never been fabricated from graphene directly. Here, it is shown by quantum molecular-dynamics simulations and classical continuum-elasticity modeling, that graphene nanoribbons can, indeed, be transformed into carbon nanotubes by means of twisting. The chiralities of the tubes thus fabricated can be not only predicted but also externally controlled. This twisting route is an opportunity for nanofabrication, and is easily generalizable to ribbons made of other planar nanomaterials.
Continuum elastic sphere vibrations as a model for low-lying optical modes in icosahedral quasicrystals
2004
The nearly dispersionless, so-called "optical" vibrational modes observed by inelastic neutron scattering from icosahedral Al-Pd-Mn and Zn-Mg-Y quasicrystals are found to correspond well to modes of a continuum elastic sphere that has the same diameter as the corresponding icosahedral basic units of the quasicrystal. When the sphere is considered as free, most of the experimentally found modes can be accounted for, in both systems. Taking into account the mechanical connection between the clusters and the remainder of the quasicrystal allows a complete assignment of all optical modes in the case of Al-Pd-Mn. This approach provides support to the relevance of clusters in the vibrational prop…
Enhanced Reflectivity Change and Phase Shift of Polarized Light: Double Parameter Multilayer Sensor
2022
Herein, the concept of point of darkness based on polarized light phase difference and absorption of light is demonstrated by simulations using low refractive index and extinction coefficient semiconductor and dielectric, and high refractive index nonoxidizing metal multilayer thin film structures. Several multilayer sensor configurations show great sensitivity to thickness and refractive index variation of the detectable material by measuring the reflectivity ratio {\Psi} and phase shift {\Delta}. Focus is on such multilayers, which have sensitivity to both parameters ({\Psi}, {\Delta}) in the visible spectral range, thus opening the possibility for further research on a new biomedical sen…