Focusing of laser-generated ion beams by a plasma cylinder: similarity theory and the thick lens formula

It is shown that plasma-based optics can be used to guide and focus highly divergent laser-generated ion beams. A hollow cylinder is considered, which initially contains a hot electron population. Plasma streaming toward the cylinder axis maintains a focusing electrostatic field due to the positive radial pressure gradient. The cylinder works as thick lens, whose parameters are obtained from similarity theory for freely expanding plasma in cylindrical geometry. Because the lens parameters are energy dependent, the lens focuses a selected energy range of ions and works as a monochromator. Because the focusing is due to the quasineutral part of the expanding plasma, the lens parameters depend on the hot electron temperature $T_e$ only, and not their density

Relativistic Doppler effect: universal spectra and zeptosecond pulses

We report on a numerical observation of the train of zeptosecond pulses produced by reflection of a relativistically intense femtosecond laser pulse from the oscillating boundary of an overdense plasma because of the Doppler effect. These pulses promise to become a unique experimental and technological tool since their length is of the order of the Bohr radius and the intensity is extremely high $\propto 10^{19}$ W/cm$^2$. We present the physical mechanism, analytical theory, and direct particle-in-cell simulations. We show that the harmonic spectrum is universal: the intensity of $n$th harmonic scales as $1/n^{p}$ for $n < 4\gamma^2$, where $\gamma$ is the largest $\gamma$--factor of the electron fluid boundary, $p=3$ and $p=5/2$ for the broadband and quasimonochromatic laser pulses respectively.Comment: 4 figure

Theory of high harmonic generation in relativistic laser interaction with overdense plasma

High harmonic generation due to the interaction of a short ultra relativistic laser pulse with overdense plasma is studied analytically and numerically. On the basis of the ultra relativistic similarity theory we show that the high harmonic spectrum is universal, i.e. it does not depend on the interaction details. The spectrum includes the power law part $I_n\propto n^{-8/3}$ for $n<\sqrt{8\alpha}\gamma_{\max}^3$, followed by exponential decay. Here $\gamma_{\max}$ is the largest relativistic $\gamma$-factor of the plasma surface and $\alpha$ is the second derivative of the surface velocity at this moment. The high harmonic cutoff at $\propto \gamma_{\max}^3$ is parametrically larger than the $4 \gamma_{\max}^2$ predicted by the ``oscillating mirror'' model based on the Doppler effect. The cornerstone of our theory is the new physical phenomenon: spikes in the relativistic $\gamma$-factor of the plasma surface. These spikes define the high harmonic spectrum and lead to attosecond pulses in the reflected radiation.Comment: 12 pages, 9 figure

Ground Beetles (Coleoptera, Carabidae) Assemblages Features Formation in Large and Medium Industrial Cities of Russia (The Case Study in Kazan, Kemerovo and Grozny)

The article presents the results of the analysis of the Carabid fauna of three cities: Grozny, Kemerovo, Kazan. It was established that communities of ground beetles clearly respond to varying degrees of recreation by changing the biotopic distribution and ecological structure: the emergence of super dominant species, a decrease in the abundance of zoophages, an increase in the share of stratobionts, and the presence of indicator species

Расчёт времени движения и скорости вагона на промежуточном участке сортировочной горки при попутном ветре

The dynamics of the car rolling from a hump yard at a railway station is studied in its various aspects. The authors have also touched upon this topic repeatedly (see, in particular, World of Transport and Transportation, 2015, Iss. 6). However, earlier reports lacked estimates of time of movement and speed of a car on the intermediate section of the hump yard under the influence of tail wind of low speed. The published article fills this gap, introduces the results of calculations, mathematical and graphical dependencies enabling to make certain generalizations and conclusions.Динамика скатывания вагона с сортировочной горки на железнодорожной станции изучается в разных ее аспектах. В том числе этой темы неоднократно касались и авторы (см., в частности, «МТ», 2015, № 6). Однако в ранее сделанных расчетах не доставало оценок времени движения и скорости вагона на промежуточном участке горки при воздействии попутного ветра малой величины. Публикуемая статья восполняет этот пробел, знакомит с результатами вычислений, математическими и графическими зависимостями,позволяющими сделать определенные обобщения и выводы

Движение вагона на сортировочной горке при попутном ветре

Mathematical modeling of the first intermediate section of a hump yard at the impact on the car of tail wind of small value is presented. The applied method is D'Alembert principle in coordinate form with non-ideal bond. Simple in appearance, analytical formulas were obtained for determining time of car movement at a hump yard, according to the value of which speed of its rolling into the end of the settlement area is determined. It was revealed that the time, during which the car rolling at this section of the hump yard depends on inclination angle, initial speed and acceleration of the car, as well as controlled length of movement.Математическое моделирование первого промежуточного участка сортировочной горки при воздействии на вагон попутного ветра малой величины. Метод - принцип Даламбера в координатной форме с неидеальной связью. Получены простые на вид аналитические формулы для определения времени движения вагона на горке, по величине которой находится значение скорости его скатывания в конце расчетного участка. Выявлено, что время, в течение которого происходит скатывание вагона на этом участке горки, зависит от угла наклона, начальной скорости и ускорения вагона, а также контролируемой длины движения

Determination of the Carrier-Envelope Phase of Few-Cycle Laser Pulses with Terahertz-Emission Spectroscopy

The availability of few-cycle optical pulses opens a window to physical phenomena occurring on the attosecond time scale. In order to take full advantage of such pulses, it is crucial to measure and stabilise their carrier-envelope (CE) phase, i.e., the phase difference between the carrier wave and the envelope function. We introduce a novel approach to determine the CE phase by down-conversion of the laser light to the terahertz (THz) frequency range via plasma generation in ambient air, an isotropic medium where optical rectification (down-conversion) in the forward direction is only possible if the inversion symmetry is broken by electrical or optical means. We show that few-cycle pulses directly produce a spatial charge asymmetry in the plasma. The asymmetry, associated with THz emission, depends on the CE phase, which allows for a determination of the phase by measurement of the amplitude and polarity of the THz pulse