Fluctuation properties of laser light after interaction with an atomic system: comparison between two-level and multilevel atomic transitions

The complex internal atomic structure involved in radiative transitions has an effect on the spectrum of fluctuations (noise) of the transmitted light. A degenerate transition has different properties in this respect than a pure two-level transition. We investigate these variations by studying a certain transition between two degenerate atomic levels for different choices of the polarization state of the driving laser. For circular polarization, corresponding to the textbook two-level atom case, the optical spectrum shows the characteristic Mollow triplet for strong laser drive, while the corresponding noise spectrum exhibits squeezing in some frequency ranges. For a linearly polarized drive, corresponding to the case of a multilevel system, additional features appear in both optical and noise spectra. These differences are more pronounced in the regime of a weakly driven transition: whereas the two-level case essentially exhibits elastic scattering, the multilevel case has extra noise terms related to spontaneous Raman transitions. We also discuss the possibility to experimentally observe these predicted differences for the commonly encountered case where the laser drive has excess noise in its phase quadrature.Comment: New version. Accepted for publication in Physical Review

Eddy current modelling using multi-layer perceptron neural networks for detecting surface cracks

A new method for computing fracture mechanics parameters using computational Eddy Current Modelling by Multi-layer Perceptron Neural Networks for detecting surface cracks. The method is based upon an inverse problem using an Artificial Neural Network (ANN) that simulates mapping between Eddy current signals and crack profiles. Simultaneous use of ANN by MLP can be very helpful for the localization and the shape classification of defects. On the other side, it can be described as the task of reconstructing the cracks and damage in the plate profile of  an  inspected  specimen  in  order  to  estimate  its  material properties. This is accomplished by inverting eddy current probe impedance measurements that are recorded as a function of probe position, excitation frequency or both. In eddy current nondestructive evaluation, this is widely recognized as a complex theoretical problem whose solution is likely to have a significant impact on the detection of cracks in material

Precision measurement of branching fractions of Ba 138 +: Testing many-body theories below the 1% level

10.1103/PhysRevA.91.040501Physical Review A - AtomicMolecularand Optical Physics91

Effects of quadratic drag on natural convection in a tilted porous layer with uniform heat flux from the side

This paper reports a numerical study of natural convection in an inclined enclosure filled with a fluid-saturated porous medium. The Darcy-Dupuit model, which includes effects of flow form drag, is used to describe the flow in the porous layer. Thermal boundary conditions of the Neumann type are applied on the long side walls of the enclosure while the short ones are assumed adiabatic. The governing parameters for the problem are the Rayleigh number R, inclination angle \u3c6, form drag parameter G and aspect ratio of the cavity A. A semi-analytical solution, valid for an infinite layer (A 6b 1), is derived on the basis of the parallel flow approximation. It is demonstrated that both the inclination of the layer and the form drag parameter, have a strong influence on the strength of the natural convection heat transfer within the enclosure. The effect of form drag parameter on the existence of multiple steady state solutions, that are possible for an enclosure slightly inclined around the horizontal position, is investigated. For boundary layer flows in a vertical cavity it is demonstrated that, in the limit of Dupuit regime, the Nusselt number is given by Nu=0.556(R/G)1/4. A good agreement is found between the predictions of the parallel flow approximation and the numerical results obtained by solving the full governing equations.Peer reviewed: YesNRC publication: Ye

An exacting transition probability measurement - A direct test of atomic many-body theories

10.1038/srep29772Scientific Reports62977