Sergey Rykovanov

Ion acceleration with ultra-thin foils using elliptically polarized laser pulses

We present theoretical considerations on the process of ion acceleration with ultra-thin foils irradiated by elliptically polarized, highly intense laser pulses. Very recently the radiation pressure acceleration regime was predicted where mono-energetic ion bunches can be produced with high efficiencies (Klimo et al 2008 Phys. Rev. ST Accel. Beams 11 031301; Robinson et al 2008 New J. Phys. 10 013021). We have studied the process by means of 1D particle-in-cell (PIC) simulations and analytical models and have considered effects of areal mass density of the target and laser ellipticity on the ion acceleration process. For certain target densities and laser parameters the optimum target thickness has been extracted. Peaked ion spectra are found for ellipticity beyond a threshold value of about 0.7. Here, we highlight the drastic difference between linear and circular polarization by movie animations.

Intense single attosecond pulses from surface harmonics using the polarization gating technique

Harmonics generated at solid surfaces interacting with relativistically strong laser pulses are a promising route towards intense attosecond pulses. In order to obtain single attosecond pulses one can use few-cycle laser pulses with carrier-envelope phase stabilization. However, it appears feasible to use longer pulses using polarization gating—the technique known for a long time from gas harmonics. In this paper, we investigate in detail a specific approach to this technique on the basis of one-dimensional-particle-in-cell (1D PIC) simulations, applied to surface harmonics. We show that under realistic conditions polarization gating results in significant temporal confinement of the harmonics emission allowing thus the generation of intense single attosecond pulses. We study the parameters needed for gating only one attosecond pulse and show that this technique is applicable to both normal and oblique incidence geometry.

Relativistic electron mirrors from nanoscale foils for coherent frequency upshift to the extreme ultraviolet

Reflecting light from a mirror moving close to the speed of light has been envisioned as a route towards producing bright X-ray pulses since Einstein’s seminal work on special relativity. For an ideal relativistic mirror, the peak power of the reflected radiation can substantially exceed that of the incident radiation due to the increase in photon energy and accompanying temporal compression. Here we demonstrate for the first time that dense relativistic electron mirrors can be created from the interaction of a high-intensity laser pulse with a freestanding, nanometre-scale thin foil. The mirror structures are shown to shift the frequency of a counter-propagating laser pulse coherently from the infrared to the extreme ultraviolet with an efficiency >104 times higher than in the case of incoherent scattering. Our results elucidate the reflection process of laser-generated electron mirrors and give clear guidance for future developments of a relativistic mirror structure.

3D simulations of surface harmonic generation with few-cycle laser pulses

The mechanism of harmonic generation in the interaction of short laser pulses with solid targets holds promise for the production of intense attosecond pulses. Using the three-dimensional code ILLUMINATION ,w e have performed simulations pertaining to an experimentally realizable parameter range by high-power laser systems to become available in the near future. The emphasis of the investigation is on the coherent nature of the emission. We studied the influence of the plasma scale length on the harmonic efficiency, angular distribution and the focusability using a post processing scheme in which the far-field of the emission is calculated. It is found that the presence of an extended density profile reduces significantly the transverse coherence length of the emitted extreme ultraviolet (XUV) light. The different stages of the interaction for two particular cases can be followed with the help of movies.

Temporal characterization of attosecond pulses emitted from solid-density plasmas

The generation of high harmonics from solid-density plasmas promises the production of attosecond (as) pulses orders of magnitude brighter than those from conventional rare gas sources. However, while spatial and spectral emission of surface harmonics has been characterized in detail in many experiments proof that the harmonic emission is indeed phase locked and thus bunched in as-pulses has only been delivered recently (Nomura et al 2009 Nat. Phys. 5 124–8). In this paper, we discuss the experimental setup of our extreme ultraviolet (XUV) autocorrelation (AC) device in detail and show the first two-photon ionization and subsequent AC experiment using solid target harmonics. In addition, we describe a simple analytical model to estimate the chirp between the individual generated harmonics in the sub- and mildly relativistic regime and validate it using particle-in-cell (PIC) simulations. Finally, we propose several methods applicable to surface harmonics to extend the temporal pulse characterization to higher photon energies and for the reconstruction of the spectral phase between the individual harmonics. The experiments described in this paper prove unambiguously that harmonic emission from solid-density plasmas indeed occurs as a train of sub-femtosecond pulses and thus fulfills the most important property for a next-generation as-pulse source of unprecedented brightness.

Dynamics of Nanometer-Scale Foil Targets Irradiated with Relativistically Intense Laser Pulses

In this letter we report on an experimental study of high harmonic radiation generated in nanometer-scale foil targets irradiated under normal incidence. The experiments constitute the rst unambiguous observation of odd-numbered relativistic harmonics generated by the ~ ~ B component of the Lorentz force verifying a long predicted property of solid target harmonics. Simultaneously the observed harmonic spectra allow in-situ extraction of the target density in an experimental scenario which is of utmost interest for applications such as ion acceleration by the radiation pressure of an ultraintense laser.

Plasma surface dynamics and smoothing in the relativistic few-cycle regime

Efficient production of coherent harmonic radiation from solid targets relies critically on the formation of smooth, short density scalelength plasmas. Recent experimental results (Dromey et al 2009 Nat. Phys. 5 146) suggest, however, that the target roughness on the scale of the emitted harmonic wavelength does not result in diffuse reflection?in apparent contradiction to the Rayleigh criterion for coherent reflection. In this paper we show, for the first time, using analytic theory and 2D PIC simulations, that the interaction of relativistically strong laser pulses with corrugated target surfaces results in a highly effective smoothing of the interaction surface and consequently the generation of highly collimated and temporally confined XUV pulses from rough targets, in excellent agreement with experimental observations.

Factors influencing the temporal characteristics of coherent wake field harmonic emission from solid surfaces

The temporal characteristics of the harmonic emission from solid targets irradiated with intense laser pulses is examined in detail. In the case where the CoherentWake Emission mechanism is dominant it is found that indeed the harmonics thus produced possess a frequency chirp resulting in non Fourier-Transform-Limited pulses. A simple model explains the underlying physics while Particle-In-Cell simulations support the conclusions drawn.

γ -Ray Generation from Plasma Wakefield Resonant Wiggler

A flexible gamma-ray radiation source based on the resonant laser-plasma wakefield wiggler is proposed. The wiggler is achieved by inducing centroid oscillations of a short laser pulse in a plasma channel. Electrons (self-)injected in such a wakefield experience both oscillations due to the transverse electric fields and energy gain due to the longitudinal electric field. The oscillations are significantly enhanced when the laser pulse centroid oscillations are in resonance with the electron betatron oscillations, extending the radiation spectrum to the gamma-ray range. The polarization of the radiation can be easily controlled by adjusting the injection of the laser pulse into the plasma channel.

Few-Cycle Ultrahigh-Contrast Light Pulses for Single Attosecond Pulses in the Relativistic Regime

We demonstrate generation of few-cycle light pulses with an ultrahigh contrast reaching 1014 25 ps before the pulse’s peak. Irradiating solid targets with our light source, we have obtained relativistic high-order harmonics that are significantly broadened and overlapped.