Search results for "Physics::Optics"
showing 10 items of 1958 documents
Modulation of surface plasmon coupling-in by one-dimensional surface corrugation
2008
Surface plasmon-polaritons have recently attracted renewed interest in the scientific community for their potential in sub-wavelength optics, light generation and non-destructive sensing. Given that they cannot be directly excited by freely propagating light due to their intrinsical binding to the metal surface, the light-plasmon coupling efficiency becomes of crucial importance for the success of any plasmonic device. Here we present a comprehensive study on the modulation (enhancement or suppression) of such coupling efficiency by means of one-dimensional surface corrugation. Our approach is based on simple wave interference and enables us to make quantitative predictions which have been …
High-Resolution Nonlinear Raman-Spectroscopy in Gases
1990
0377-0486; The resolution in the Raman spectra of gases has been greatly improved by the development of the different methods of non-linear Raman scattering. When two laser beams, one of which has a tunable frequency, are focused in a sample, a stimulated Raman process occurs as soon as the frequency difference between the two lasers is equal to a Raman-active rovibrational or rotational transition frequency. The Raman resonance can be detected in different ways: by coherent anti-Stokes Raman scattering (CARS) or the corresponding Stokes process (CSRS), by a gain in one of the beams (stimulated Raman gain spectroscopy, SRGS) or a loss in the other (inverse Raman spectroscopy, IRS), or even …
Parametric Solitons in Two-Dimensional Lattices of Purely Nonlinear Origin
2008
We demonstrate spatial solitons via twin-beam second-harmonic generation in hexagonal lattices realized by poling lithium niobate planar waveguides. These simultons can be steered by acting on power, direction, and wavelength of the fundamental frequency input.
Photons, Photon Jets and Dark Photons at 750 GeV and Beyond
2016
In new physics searches involving photons at the LHC, one challenge is to distinguish scenarios with isolated photons from models leading to "photon jets". For instance, in the context of the 750 GeV diphoton excess, it was pointed out that a true diphoton resonance $S \to \gamma\gamma$ can be mimicked by a process of the form $p p \to S \to a a \to 4\gamma$, where $S$ is a new scalar with a mass of 750 GeV and $a$ is a light pseudoscalar decaying to two collinear photons. Photon jets can be distinguished from isolated photons by exploiting the fact that a large fraction of photons convert to an $e^+e^-$ pair inside the inner detector. In this note, we quantify this discrimination power, an…
Probing ultrafast changes of spin and charge density profiles with resonant XUV magnetic reflectivity at the free-electron laser FERMI
2017
We report the results of resonant magnetic XUV reflectivity experiments performed at the XUV free-electron laser FERMI. Circularly polarized XUV light with the photon energy tuned to the Fe M2,3 edge is used to measure resonant magnetic reflectivities and the corresponding Q-resolved asymmetry of a Permalloy/Ta/Permalloy trilayer film. The asymmetry exhibits ultrafast changes on 240 fs time scales upon pumping with ultrashort IR laser pulses. Depending on the value of the wavevector transfer Qz, we observe both decreasing and increasing values of the asymmetry parameter, which is attributed to ultrafast changes in the vertical spin and charge density profiles of the trilayer film.
Reference-Plane Invariant Method for Measuring Electromagnetic Parameters of Materials
2010
This paper presents a simple and effective wideband method for the determination of material properties, such as the complex index of refraction and the complex permittivity and permeability. The method is explicit (non-iterative) and reference-plane invariant: it uses a certain combination of scattering parameters in conjunction with group-velocity data. This technique can be used to characterize both dielectric and magnetic materials. The proposed method is verified experimentally within a frequency range between 2 to 18 GHz on polytetrafluoroethylene and polyvinylchloride samples. A comprehensive error and stability analysis reveals that, similar to other methods based on transmission/re…
Electric polarization of Onsager fluids
2002
The problem of correct determination of electrical and optical characteristics of molecules of dielectric fluids can actually be brought to problem of description of the effective internal field which consist of the field included by external sources and the cumulate electric field of molecules on the medium including intermolecular interactions. An attempt was made to modify the model Onsager theory. A polarizable molecular dipole enclosed in spherical cavity is substituted for a rigid one submerged in polarizable medium which fills the cavity. The local dielectric permittivity of the Heaviside type is replaced for the oscillating, rapidly damping function of Fresnel integral. The analytic…
Imprinting the complex dielectric permittivity of liquids into the spintronic terahertz emission
2021
We report an approach in time-domain terahertz (THz) spectroscopy for measuring the dielectric response of liquids based on inherent properties of spintronic THz emitters (STEs). The THz electric field radiated from the STE is inversely proportional to the sum of the complex refractive indices of the media surrounding the thin metallic stack of the STE and the stack's conductivity. We demonstrate that by bringing a liquid in contact with the emitter, its complex refractive index and accordingly its dielectric response are imprinted into the radiated electromagnetic field from the emitter. We use water as the test liquid and ascertain its dielectric loss and permittivity in the range of ∼0.…
Dielectric response of α-LiIO3 acid type crystals
1998
Abstract α-LiIO 3 is often used as non-linear optical material. In view of its preparation, low pH aqueous solutions are used as mother solutions, which give crystals with some hydrogen incorporated to the lattice. Thus, dielectric characterization appears as a very important tool. In this work, the dielectric properties of acid type α-LiIO 3 crystals (conductivity, permittivity, loss-angle tangent) are investigated as functions of temperature and frequency, through an original method allowing seemingly continuous measurements and avoiding space charge contributions to the measurements. The results show the dipolar and low frequency conductivity contributions to the dielectric response. The…
Nonresonant dielectric hole-burning spectroscopy on a titanium-modified lead magnesium niobate ceramic
2001
Nonresonant dielectric hole-burning experiments were performed on the titanium-modified relaxor ferroelectric lead magnesium niobate around the diffuse maximum in the dielectric permittivity. After applying large alternating electric pump fields we monitored the polarization response to small field steps for times between 0.3 ms and 100 s. Depending on the frequency of the pump oscillation a speedup of the polarization response was observed with a maximum located around times corresponding to the inverse pump frequency. The refilling of the dielectric holes was investigated for several temperatures, pump frequencies, and pump field amplitudes. It proceeded always slower than the time scale …