Transient Cherenkov radiation from an inhomogeneous string excited by an ultrashort laser pulse at superluminal velocity

An optical response of one-dimensional string made of dipoles with a periodically varying density excited by a spot of light moving along the string at the superluminal (sub-luminal) velocity is theoretically studied. The Cherenkov radiation in such system is rather unusual, possessing both transient and resonant character. We show that under certain conditions, in addition to the resonant Cherenkov peak another Doppler-like frequency appears in the radiation spectrum. Both linear (small-signal) and nonlinear regimes as well as different string topologies are considered.Comment: accepted to Phys. Rev.

Effect of the superconducting wiggler on the DELSY beam dynamics

The project DELSY is being under development at JINR, Dubna, Russia. This synchrotron radiation source is dedicated to the investigation on condensed matter physics, atomic physics, biology, medicine, chemistry, micromechanics, lithography and others. The storage ring DELSY is an electron storage ring with the beam energy 1.2 GeV and 4 straight sections to accommodate accelerator equipment and insertion devices. One of the straight sections is intended for a 10 T superconducting wiggler (wavelength shifter) and one for the undulator with 150 periods and a magnetic field of 0.75 T. The wiggler will influence many aspects of beam dynamics: linear motion, dynamic aperture, emittance, damping times etc. The problem is rather serious for the DELSY machine because the energy of the electron beam is small while the wiggler's magnetic field is strong. In this paper we consider two models of the wiggler's magnetic field with and without the focusing caused by the sextupolar field of the wiggler as we need to develop the requirements to the wiggler design. We study the influence of the 10 T wiggler on the beam dynamics in the DELSY storage ring and propose a possible scheme to cure it. The combined work of the insertion device is presented too.Comment: 17 pages, submitted to journal NIM

Enhancing entanglement detection of quantum optical frequency combs via stimulated emission

We investigate the performance of a certain nonclassicality identifier, expressed via integrated second-order intensity moments of optical fields, in revealing bipartite entanglement of quantum-optical frequency combs (QOFCs), which are generated in both spontaneous and stimulated parametric down-conversion processes. We show that, by utilizing that nonclassicality identifier, one can well identify the entanglement of the QOFC directly from the experimentally measured intensity moments without invoking any state reconstruction techniques or homodyne detection. Moreover, we demonstrate that the stimulated generation of the QOFC improves the entanglement detection of these fields with the nonclassicality identifier. Additionally, we show that the nonclassicality identifier can be expressed in a factorized form of detectors quantum efficiencies and the number of modes, if the QOFC consists of many copies of the same two-mode twin beam. As an example, we apply the nonclassicality identifier to two specific types of QOFC, where: (i) the QOFC consists of many independent two-mode twin beams with non-overlapped spatial frequency modes, and (ii) the QOFC contains entangled spatial frequency modes which are completely overlapped, i.e., each mode is entangled with all the remaining modes in the system. We show that, in both cases, the nonclassicality identifier can reveal bipartite entanglement of the QOFC including noise, and that it becomes even more sensitive for the stimulated processes.Comment: 11 p., 8 fig