Search results for "Physics::Optics"
showing 10 items of 1958 documents
Collapse and revival of a Dicke-type coherent narrowing in potassium vapor confined in a nanometric-thin cell
2015
A nanometer-thin-cell (in the direction of laser beam propagation) has been elaborated with the thickness of the atomic vapor column varying smoothly in the range of $L = \unit[50-1500]{nm}$. The cell allows one to study the behavior of the resonance absorption over the $D_1$ line of potassium atoms by varying the laser intensity and the cell thickness from $L = \lambda / 2$ to $L = 2 \lambda$ with the step $\lambda/2$ ($\lambda =\unit[770]{nm}$ is the resonant wavelength of the laser). It is shown that despite the huge Doppler broadening ($>\unit[0.9]{GHz}$ at the cell temperature $\unit[170]{^{\circ}C}$), at low laser intensities a narrowing of the resonance absorption spectrum is observe…
On the Rigorous Calculation of All Ohmic Losses in Rectangular Waveguide Multi-Port Junctions
2005
In this paper, all ohmic losses effects present in rectangular waveguide multi-port junctions are rigorous and efficiently computed. For this purpose, a new formulation based on the theory of cavities, which provides generalized admittance matrix representations for such junctions, is proposed. To validate this theory, we have successfully compared our results with numerical data of a lossy E-plane T-junction and of a hollow waveguide, as well as with experimental measurements of a real H-plane T-junction.
Control of nonlinear processes in two-photon excited rubidium vapour by resonant laser light
2019
Frequency up- and down-conversion in warm alkali vapours over a range of applied cw laser intensities has received much attention in recent years due to promising applications in the fields of remote detection, quantum information and computing, specifically in the implementation of correlated photon pairs, photon storage and quantum memory interface to name a few. The generation of directional laser-like blue and infrared light in alkali vapours has been extensively studied. However, important details of the interplay of parametric and nonparametric nonlinear processes, such as the four-wave mixing (FWM) and amplified spontaneous emission (ASE) responsible for the new field generation, are…
Duty-ratio control of Nonlinear phase noise in dispersion-managed WDM transmissions using RZ-DPSK modulation at 10 Gb/s
2006
International audience; The authors compare analytical and numerical estimates, showing that the nonlinear phase noise of short optical pulses associated with the coupling between amplified spontaneous emission noise and fiber nonlinearity may be controlled by adjusting the duty cycle of the return-to-zero (RZ) signal modulation format. The impact of this effect in the optimization of the performance of 10-Gb/s dispersion-managed wavelength division multiplexed (WDM) systems using RZ-differential phase-shift keying (DPSK) modulation is discussed. By extensive numerical simulations, it is shown that the transmission quality of ultradense WDM systems using the RZ-DPSK modulation format may be…
Intensity spiral patterns in a semiconductor microresonator
2005
Spiral waves appear frequently in nature. They have been studied, e.g., in hydrodynamic systems, chemical reactions, and in a large variety of biological and physical systems [Grill et al., Phys. Rev. Lett. 75, 3368 (1995); Goryachev and Kapral, Phys. Rev. Lett. 76, 1619 (1996)]. In contrast to chemical and hydrodynamic processes where the field amplitude exhibits the spiral patterns (intensity spirals), in optics the spiral structures relate generally to the phase structure of the optical field (so-called 'optical vortices' [Lugiato et al., Adv. At., Mol., Opt. Phys. 40, 229 (1999); Arecchi et al., Phys. Rep. 318, 1 (1999); Weiss et al., Appl. Phys. B:Lasers Opt. B68, 151 (1999)]). Thus th…
Harmonic generation from nanorings driven by a two-color laser field
2014
We study the high harmonic generation and the polarization of the harmonics emitted by a nanoring driven by two laser fields of angular frequency ?1 and ?2, with ?2?=?2?1, and ?1 resonant between the ground and the first excited state. We show that by varying parameters, such as laser intensity, photon energy and the delay between the two laser pulses, we can control the number of harmonics and the polarization of the radiation. In particular we show that with this choice of two-laser photon frequency rate we obtain more harmonics with respect to other configurations. We also calculated the average absorbed energy and the average angular momentum acquired by the electron as a function of th…
Energy flow canalization of evanescent cylindrical-vector beams
2013
We analyzed ultra-confined vector beams with radial and azimuthal polarizations which are critically self-governed inside plasmonic metamaterials. We succeeded in the separation of polarization singularities in the fields at the nanoscale. The examined metamaterials are suitable for long-range transport of subwavelength Bessel beams without discernible blurring. These results open the door to develop integrated devices for applications such as the manipulation of polarization and angular momentum of surface-plasmon excitations.
Field Emission of Electrons Generated by the Near Field of Strongly Coupled Plasmons
2012
Field emission of electrons is generated solely by the ultrastrong near-field of strongly coupled plasmons without the help of a noticeable dc field. Strongly coupled plasmons are excited at Au nanoparticles in subnanometer distance to a Au film by femtosecond laser pulses. Field-emitted electrons from individual nanoparticles are detected by means of photoelectron emission microscopy and spectroscopy. The dependence of total electron yield and kinetic energy on the laser power proves that field emission is the underlying emission process. We derive a dynamic version of the Fowler-Nordheim equation that yields perfect agreement with the experiment.
Absolute frequency measurement of rubidium 5S-7S two-photon transitions.
2013
We report the absolute frequency measurements of rubidium 5S-7S two-photon transitions with a cw laser digitally locked to an atomic transition and referenced to an optical frequency comb. The narrow, two-photon transition, 5S-7S (760 nm) insensitive to first order in a magnetic field, is a promising candidate for frequency reference. The performed tests yield the transition frequency with accuracy better than reported previously.
Variable delay line for phased-array antenna based on a chirped fiber grating
2000
We present a theoretical and experimental analysis of the performance of phased-array antennas steered by a single chirped fiber grating. Two approaches consisting of conventional and single-sideband (SSB) modulation techniques of the optical signal are presented in order to compare their performance and suitability for beamforming applications in microwave antennas. By using a 40-cm-long chirped grating, we measure the phase and amplitude response and calculate the corresponding radiation patterns to demonstrate wide-band operation and continuous spatial scanning properties of both configurations. SSB modulation Is presented as a real alternative to the first one offering broader operation…