Relativistic Mirror Research Articles

Self-aligning concave relativistic plasma mirror with adjustable focus

We report an experimental-computational study of the optical properties of plasma mirrors (PMs) at the incident laser frequency when irradiated directly at relativistic intensity (1018<I0<1019 W/cm2) by near-normally incident (4°), high-contrast, 30 fs, 800 nm laser pulses. We find that such relativistic PMs are highly reflective (0.6–0.8) and focus a significant fraction of reflected light to intensity as large as ∼10I0 at distance f as small as ∼25 μm from the PM, provided that pre-pulses do not exceed 1014 W/cm2 prior to ∼20 ps before arrival of the main pulse peak. Particle-in-cell simulations show that focusing results from denting of the reflecting surface by light pressure combined with relativistic transparency and that reflectivity and f can be adjusted by controlling pre-plasma length L over the range 0.5 ≲ L ≲ 3 μm. Pump-probe reflectivity measurements show that the PM's focusing properties evolve on a ps time scale.

Bright high-order harmonic generation with controllable polarization from a relativistic plasma mirror.

Ultrafast extreme ultraviolet (XUV) sources with a controllable polarization state are powerful tools for investigating the structural and electronic as well as the magnetic properties of materials. However, such light sources are still limited to only a few free-electron laser facilities and, very recently, to high-order harmonic generation from noble gases. Here we propose and numerically demonstrate a laser–plasma scheme to generate bright XUV pulses with fully controlled polarization. In this scheme, an elliptically polarized laser pulse is obliquely incident on a plasma surface, and the reflected radiation contains pulse trains and isolated circularly or highly elliptically polarized attosecond XUV pulses. The harmonic polarization state is fully controlled by the laser–plasma parameters. The mechanism can be explained within the relativistically oscillating mirror model. This scheme opens a practical and promising route to generate bright attosecond XUV pulses with desirable ellipticities in a straightforward and efficient way for a number of applications.

Nonlinear reflection of high-amplitude laser pulses from relativistic electron mirrors

A coherent X-ray pulse of attosecond duration can be formed in the reflection of a counterpropagating laser pulse from a relativistic electron mirror. The reflection of a high-amplitude laser pulse from the relativistic electron mirror located in the field of an accelerating laser pulse is investigated by means of two-dimensional (2D) numerical simulation. It is shown that provided the amplitude of the counterpropagating laser pulse is several times greater than the amplitude of the accelerating laser pulse, the reflection process is highly nonlinear, which causes a significant change in the X-ray pulse shape and its shortening up to generation of quasi-unipolar pulses and single-cycle pulses. A physical mechanism responsible for this nonlinearity of the reflection process is explained, and the parameters of the reflected X-ray pulses are determined. It is shown that the duration of these pulses may constitute 50 – 60 as, while their amplitude may be sub-relativistic.

Relativistically strong electromagnetic radiation in a plasma

Physical processes in a plasma under the action of relativistically strong electromagnetic waves generated by high-power lasers have been briefly reviewed. These processes are of interest in view of the development of new methods for acceleration of charged particles, creation of sources of bright hard electromagnetic radiation, and investigation of macroscopic quantum-electrodynamical processes. Attention is focused on nonlinear waves in a laser plasma for the creation of compact electron accelerators. The acceleration of plasma bunches by the radiation pressure of light is the most efficient regime of ion acceleration. Coherent hard electromagnetic radiation in the relativistic plasma is generated in the form of higher harmonics and/or electromagnetic pulses, which are compressed and intensified after reflection from relativistic mirrors created by nonlinear waves. In the limit of extremely strong electromagnetic waves, radiation friction, which accompanies the conversion of radiation from the optical range to the gamma range, fundamentally changes the behavior of the plasma. This process is accompanied by the production of electron–positron pairs, which is described within quantum electrodynamics theory.

General principles for reflection of laser pulse from a relativistic uniformly-moving mirror

Abstract We investigate the reflection of laser pulse from a uniformly moving mirror at relativistic speeds in the general case of inclined mirrors. We use geometrical optics to derive general relations for length, frequency, wavelength and electric field of the pulse after reflection from inclined mirror in the lab frame. In addition, the pulse geometric deformation from reflection is investigated and simulated in two dimensions.

Self-consistent theory of high-order harmonic generation by relativistic plasma mirror

We present a self-consistent semianalytical model of the relativistic plasma mirror, based on the exact computation of the laser-driven electron surface oscillations within the cold-fluid approximation. Valid for arbitrary solid densities, laser incidence angle, and a large set of laser intensities (10(18)-10(21) W/cm(2)), the model unravels different regimes of harmonic generation. In particular, it is found that efficient conversion of p-polarized laser pulses into high-order harmonics well above the plasma frequency requires either high laser intensities, low plasma densities, or incidence angles larger than a threshold value. This critical angle corresponds to a transition between a regime where the electron surface dynamics is mostly governed by the laser J×B force and a "cyclotron Brunel" regime, where electrons perform many cyclotron gyrations when moving into the vacuum. Under conditions relevant to current laser experiments, the latter regime gives rise to nonmonotonic variations of the harmonic yield with the laser field. Our predictions are supported by an extensive parametric study performed with highly resolved one-dimensional particle-in-cell simulations.

Interference in multilayer relativistic mirrors

In this paper, reflection coefficient of a relativistic ultra-thin electron multilayer is calculated using electromagnetic interference procedures. The relativistic electron layers are assumed to be formed by nonlinear plasma wake waves that constitute the electron density cusps. It is shown that the interference between successive relativistic mirrors is restricted by the condition, τp≫(2γ0)5/2/ωp0, where τp is the laser pulse duration. The results showed that tailoring the pulse amplitude, incident wave frequency value, incidence angle, and plasma density leads to increasing reflection coefficient a few orders of magnitudes. This constructive interference condition can be used for increasing conversion efficiency in the reflected energy from relativistic mirrors for the purpose of generating ultra-short coherence pulses in the extreme ultraviolet and x-ray regions. We also performed reflection from relativistic thin electron layers using relativistic 1D3V electromagnetic particle-in-cell (PIC) simulation. It was found that the results of PIC simulation are in agreement with analytical considerations.

Coherent kilo-electron-volt backscattering from plasma-wave boosted relativistic electron mirrors

A different parameter regime of laser wakefield acceleration driven by sub-petawatt femtosecond lasers is proposed, which enables the generation of relativistic electron mirrors further accelerated by the plasma wave. Integrated particle-in-cell simulation, including both the mirror formation and Thomson scattering, demonstrates that efficient coherent backscattering up to keV photon energy can be obtained with moderate driving laser intensities and high density gas targets.

The parametric doppler effect upon oblique radiation incidence in quartz glass

Frequency and reflection angle of probe radiation from a refractive-index inhomogeneity induced by an intense pumping pulse in quartz glass and moving with a relativistic velocity are calculated. Conditions under which the normal component of the wave vector of the reflected wave is directed to the opposite or to the same direction as the same component for the incident wave are determined. Comparison with the case of radiation reflection from a relativistic mirror in vacuum is performed. Conditions of the appearance of the Vavilov-Cherenkov radiation from a relativistic refractive-index inhomogeneity induced in the medium by an intense laser pulse are discussed.

Single cycle thin film compressor opening the door to Zeptosecond-Exawatt physics

This article demonstrates a new compression scheme that has the potential to compress a high energy pulse as high as a few hundred Joules in a pulse as short as one optical cycle at 0.8{\mu}m making a true ultra-relativistic {\lambda}^3 pulse. This pulse could have a focused intensity of 10^24W/cm2 or a0 of 1000. It could form an efficient, 10%, relativistic mirror that could compress the pulse to the atto-zeptosecond regime, with an upshifted wavelength of 1-10keV. This technique could be a watershed making the entry of petawatt pulses into the exawatt and zeptosecond regime possible.

Imperfect relativistic mirrors in the quantum regime

The collective backscattering of intense laser radiation by energetic electron beams is considered in the relativistic quantum regime. Exact solutions for the radiation field are obtained, for arbitrary electron pulse shapes and laser intensities. The electron beams act as imperfect nonlinear mirrors on the incident laser radiation. This collective backscattering process can lead to the development of new sources of ultra-short pulse radiation in the gamma-ray domain. Numerical examples show that, for plausible experimental conditions, intense pulses of gamma-rays, due to the double Doppler shift of the harmonics of the incident laser radiation, can be produced using the available technology, with durations less than 1 as.

Optical properties of relativistic plasma mirrors

The advent of ultrahigh-power femtosecond lasers creates a need for an entirely new class of optical components based on plasmas. The most promising of these are known as plasma mirrors, formed when an intense femtosecond laser ionizes a solid surface. These mirrors specularly reflect the main part of a laser pulse and can be used as active optical elements to manipulate its temporal and spatial properties. Unfortunately, the considerable pressures exerted by the laser can deform the mirror surface, unfavourably affecting the reflected beam and complicating, or even preventing, the use of plasma mirrors at ultrahigh intensities. Here we derive a simple analytical model of the basic physics involved in laser-induced deformation of a plasma mirror. We validate this model numerically and experimentally, and use it to show how such deformation might be mitigated by appropriate control of the laser phase.

Robust relativistic electron mirrors in laser wakefields for enhanced Thomson backscattering

By adopting an up-ramp density profile, we propose to generate relativistic electron mirrors from laser-driven underdense plasma waves, which are insensitive to finite thermal temperature within a certain range. Along the density ramp, premature wavebreaking due to thermal effects is shown to be well mitigated. Under sufficiently high amplitudes of wake excitation, overcritical dense electron mirrors can pile up when approaching the end of the up-ramp. The consequent mirror speed can be stably driven to the group velocity of the laser propagating in a corresponding uniform plasma. Compared with using purely uniform but thermal plasmas, the present thermal-insensitive mirrors can provide enhanced scattering efficiency and spectral upshift for a counter-propagating probe pulse. These observations are confirmed by multi-dimensional particle-in-cell simulations.

Two-color high-order-harmonic generation: Relativistic mirror effects and attosecond pulses

In this work, an analytical and numerical study of the relativistic interaction of a linearly polarized laser field of ${\ensuremath{\omega}}_{1}$ and ${\ensuremath{\omega}}_{2}$ frequencies with highly overdense plasma at normal and oblique incidence is presented. Combining harmonics of ${\ensuremath{\omega}}_{1}$ and ${\ensuremath{\omega}}_{2}$ frequencies causes the amplitude oscillation of relativistic mirrors to be increased. Therefore, the intensity of generated harmonics will be increased considerably. Also, in agreement with the fully relativistic one-dimensional particle-in-cell (PIC) simulation, the relativistic mirror model explains the enhancement of the harmonic intensity of the upper spectra in the interaction of the two-color mixing laser pulse with overdense plasma. Our results show that increasing the intensity of high-order harmonics by using the two-color pulse will enhance sharply the intensity of ultrashort attosecond pulses.

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.

Controlling the generation of high frequency electromagnetic pulses with relativistic flying mirrors using an inhomogeneous plasma

A method for the controlled generation of intense high frequency electromagnetic fields by a breaking Langmuir wave (relativistic flying mirrors) in a gradually inhomogeneous plasma is proposed. The wave breaking threshold depends on the local plasma density gradient. Compression, chirping and frequency multiplication of an electromagnetic wave reflected from relativistic mirrors is demonstrated using Particle-In-Cell simulations. Adjusting the shape of the density profile enables control of the reflected light properties.

Generation of intense coherent attosecond X-ray pulses using relativistic electron mirrors

We analyse the steepening of the leading edge of femtosecond petawatt pulses with the use of plasma layers and show that, at an electron density several times higher than the critical one, an asymmetric (in time domain) pulse can be produced with an amplitude of the first half-wave differing little from the maximum pulse amplitude. Using numerical simulation, we have studied the interaction of such pulses with nanometre-thick films, including the generation of relativistic electron mirrors and the reflection of a counterpropagating probe pulse from such mirrors. The resulting coherent X-ray pulses have a duration of as and a power of at a wavelength of . Our results demonstrate that the reflectivity of a relativistic electron mirror situated in the accelerating pulse field is independent of the probe pulse amplitude when it increases up to the accelerating pulse amplitude.

Релятивистские зеркала в плазме — новые результаты и перспективы

Релятивистские зеркала в плазме — новые результаты и перспективы

Double relativistic electron-accelerating mirror

A numerical simulation of the interaction of a laser pulse with ultrathin targets has revealed a possibility of generating thin dense relativistic electron layers. The maximum kinetic energy of the electron mirror can be gained using an optimal combination of the target thickness and the laser pulse intensity and duration. It is proposed to use an additional (second) laser target, located at an optimal distance from the first target to cut off the laser pulse from the electron layer when the latter gains a maximum kinetic energy. This relativistic electron mirror can be used for efficient generation of ‘hard’ coherent radiation via counter reflection of an additional (probe) laser pulse from the mirror.

Possibility of measuring photon-photon scattering via relativistic mirrors

Photon-photon scattering predicted by quantum electrodynamics has not been experimentally confirmed in the optical frequency range. This is due to its extremely small cross section in this energy range. Since the cross section rapidly increases with photon energy, we propose measuring the photon-photon scattering cross section by upshifting optical lasers to the 100-eV to keV range using four relativistic mirror schemes and colliding them. In two of the schemes we find that although the number of scattering events is small with realistic laser parameters, measurement could be possible with an accumulation of a large number of laser shots. In the two other schemes a large number of scattering events is possible, however, the use of large future laser systems will be necessary.