Laser Requirements for High-Order Harmonic Generation by Relativistic Plasma Singularities

Abstract

We discuss requirements on relativistic-irradiance (I 0 > 10 18 W/cm 2) high-power (multi-terawatt) ultrashort (femtosecond) lasers for efficient generation of high-order harmonics in gas jet targets in a new regime discovered recently (Pirozhkov et al., 2012). Here, we present the results of several experimental campaigns performed with different irradiances, analyse the obtained results and derive the required laser parameters. In particular, we found that the root mean square (RMS) wavefront error should be smaller than~100 nm (~λ/8). Further, the angular dispersion should be kept considerably smaller than the diffraction divergence, i.e., µrad level for 100-300-mm beam diameters. The corresponding angular chirp should not exceed 10 −2 µrad/nm for a 40-nm bandwidth. We show the status of the J-KAREN-P laser (Kiriyama et al., 2015; Pirozhkov et al., 2017) and report on the progress towards satisfying these requirements.

Petawatt Femtosecond Laser Pulses from Titanium-Doped Sapphire Crystal

“…Currently, experiments are ongoing to generate GeV electron beams from 1-2-cm gas jet targets with a focused irradiance of 10 20 W/cm 2 . Experiments on high-order harmonics from relativistic singularities [55][56][57][58][59], on high-repetition-rate multi-MeV, pure proton beam generation from micron-scale hydrogen cluster targets [60][61][62][63], and on X-ray spectroscopy of laser-plasma interaction in the ultra-relativistic regime [64,65] are also in progress. Future prospects for high-field science include the testing of quantum electrodynamics (QED), which will be made possible even for a small facility such as KPSI, QST.…”

In-vacuum post-compression of optical probe pulses for relativistic plasma diagnostics

“…Successful implementation of this technique enables the observation of wake waves in a plasma behind the laser driver [1][2][3] , injection dynamics [4,5] and magnetic field structures [6] in electron acceleration process [7] . Significantly interesting is the optical probing of electron density singularities of a relativistic plasma [8] capable of reflecting light via the double Doppler effect in the relativistic flying mirror mechanism [9][10][11][12] or emitting bright coherent soft-X-ray radiation in the course of Burst Intensification by Singularity Emitting Radiation (BISER) [13][14][15][16][17][18] . However, images of sharply localized relativistic singularities obtained by means of ultra-short probe pulses with duration τ are blurred to sizes ∼ cτ due to the motion blur; here c is the speed of light.…”

Enhanced diagnostics of radiating relativistic singularities and BISER by nonlinear post-compression of optical probe pulse

“…The pump-probe approach based on the use of part of a femtosecond driver as a probe pulse is a handy tool for laboratory studies of femtosecond laser plasma. It can be used for investigating ultrafast processes and objects, such as wakewaves in a plasma behind the laser driver [4] and injection in electron acceleration process [5]; electron density singularities of a relativistic plasma [6] capable of reflecting light with double Doppler effect in the relativistic flying mirror mechanism [7][8][9] or emitting bright coherent soft-X-ray radiation in the course of Burst Intensification by Singularity Emitting Radiation (BISER) [2,[10][11][12][13]. The absence of jitter between the laser driver and the probe pulse allows studying the dynamics of such processes on femtosecond scale by controlling the position of the optical delay line.…”