arXiv subjects

A. H. Gevorgyan

Publications and source records attributed to A. H. Gevorgyan.

26 records · Page 2Linked to original sources

arXiv2017

Permanent Magnets Undulator for Terahertz FEL

The terahertz FEL ferromagnetic undulator has been created. The length of the undulator period is 9cm, number of the periods is 27. By means of selection and redistribution of magnetic elements the spread of amplitudes of the magnetic field was reduced to 7%. Additional windings of magnetic elements were used to compensate for residual spread. Required focusing gradient of magnetic field was obtained as a result of relative displacement of alternating poles with opposite charge of magnetic field along the x axis. Parameters of undulator including focusing properties in the horizontal plane were investigated.

physics.acc-ph↗

arXiv2017

Polarization Properties of the Cholesteric Liquid Crystals

In the present paper, we investigate the polarization properties of the cholesteric liquid crystals (CLCs) with an isotropic/anisotropic defect inside them. Possibilities of amplification of the polarization plane rotation and stabilization of the light polarization azimuth by these systems are investigated in details.

physics.optics↗

arXiv2017

Radiation Peculiarities in Chiral Photonic Crystals

The peculiarities of defect modes and reflection spectra of chiral photonic crystals (CPC) with an isotropic defect for various thicknesses of the defect layer was investigated. The peculiarities of the spectra of photonic density of the state (DOS) and those of the intensity at the center of the defect were investigated, too. It was shown that there is one more possibility of tuning of laser emission - by the change of the defect layer thickness - in CPCs doped with laser dyes (with resonance atoms) and with an isotropic defect. It was shown that the given system can work as a tunable narrow-band filter (or mirror) with tunable wavelength width and tunable location of frequency of the complete transmittance (reflection) band. The radiation peculiarities of these systems were discussed. It was shown that in certain conditions an anomalous strong radiation can be observed for defect modes, and low - threshold laser generation is possible, again, for these modes. It was also shown that radiation suppression is possible for defect modes. The peculiarities of group velocity, group velocity dispersion and nonreciprocity were studied.

physics.optics↗

arXiv2017

Cholesteric liquid crystals with tunable defect inside

Peculiarities of the defect modes of cholesteric liquid crystals (CLCs) with an isotropic/anisotropic defect inside are investigated. The influence of the defect layer thickness and its anisotropy of refraction, the influence of the system thickness and of the defect layer position in the system, as well as the influence of the dielectric borders on the defect modes is investigated. It is shown that it is possible to change reflection at the defect modes in wide intervals and change the defect mode wavelength, by tuning the defect location and its thickness. Such a system possesses transmission asymmetry. Also, the CLC system thickness and the refraction coefficient of the medium bordering the CLC layer on its both sides have essential influence on the reflection at the defect mode and on the reflection frequency.

physics.optics↗

arXiv2017

Physics of Cold Atomic Fermi Gases

We consider a cold two-species atomic Fermi gas confined in a trap. We combine the Hermitian coupling between the states (we assume them to be the states with different spins) with the Cooper pairing of atoms with these different spins. This opens up a new prospect for investigation of interplay between various phenomena involving Raman coupling (e.g., atom lasers, dark-state polaritons) and effects caused by Cooper pairing of particles (e.g., superfluidity). We have obtained a threshold of transition from oscillatory to amplifying behavior of matter waves.

cond-mat.quant-gas↗

arXiv2017

Composite Cell from Nematic and Cholesteric Liquid Crystals as an Rotator of Electrically Tunable Polarization Plane

A liquid crystal optical device made of an optically anisotropic heterostructure is considered. The device consists of a cholesteric liquid crystal (CLC) layer sandwiched by two phase-shifting anisotropic layers of a nematic liquid crystal (NLC). In this structure each of the NLC layers is a quarterwave plate. The problem is solved both by Ambartsumian method of layer addition and Muller matrix method. The peculiarities of reflection spectra, eigen polarizations, rotation of polarization plane and polarization ellipticity are studied. It is shown that this device can work as a light modulator or a system for obtaining linearly polarized light with electrically tunable rotation of the polarization plane (which is especially important for optical communication), as well as a device for obtaining the linearly polarized light from a non-polarized one.

physics.optics↗

arXiv2017

X-Ray Radiation Generation in Heat Engines Using Electron Cooling

We consider a relativistic quantum heat engine that goes through a thermodynamical cycle consisting of stages involving laser-assisted cooling of electrons and the generation of Xray radiation. Quantum treatment of the processes makes it possible to obtain the necessary condition and the amount of work extracted from the interaction ingredients, as well as the efficiency of the heat engine. We have also found that the efficiency of the relativistic engine is less than the one for the nonrelativistic case for the same momenta. The obtained results set the limits to the cooling, as well as the intensity of X-ray radiation, in the quantum regime of the interaction of electrons with laser fields.

physics.acc-ph↗

arXiv2016

Infrared Radiation from Rough Surface

We consider generation of diffusive radiation by a charged particle passing through a random stack of plates in the infrared region. Diffusive radiation originates due to multiple scattering of pseudophotons on the plates. To enhance the radiation intensity one needs to make the scattering more effective. For this goal we suggest to use materials with negative dielectric constant .

physics.acc-ph↗