Generation of XUV spectral continua from relativistic plasma mirrors driven in the near-single-cycle limit

Frederik Böhle,Rodrigo Lopez-Martens,Stefan Haessler,Maïmouna Bocoum,Maxence Thévenet,Aline Vernier

doi:10.1088/2515-7647/ab9715

Abstract

We present experiments using relativistic-intensity 1.5-cycle laser fields at 1 kHz repetition rate to drive surface high-harmonic generation (SHHG) from surface plasmas with controlled density gradient. As a function of the driving pulse carrier-envelope phase (CEP), we observe a transition from a modulated to a continuous SHHG spectrum, indicating the transition from double to isolated attosecond pulse emission. Single shot-acquisitions of XUV spectral continua support the emission of isolated attosecond pulses with an isolation degree of between 10 and 50 for the majority of the driving pulse CEPs. 2D Particle-in-cell simulations corroborate this interpretation and predict percent-level efficiencies for the generation of an isolated attosecond pulse even without spectral filtering.

Highlights

Surface high-harmonic generation (SHHG) from relativistic plasma mirrors has long been recognized as an efficient route to high-energy intense attosecond XUV pulses [1,2,3]
We report on SHHG from relativistic plasma mirrors driven by this 1.5-cycle laser, leading to XUV continua (10–25 eV) with a degree of residual spectral modulation varying as a function of the laser carrier-envelope phase (CEP) and supporting an isolated attosecond pulse with an isolation degree ≳ 25 for half of the 2π-CEP-range
This optimizes the conditions for ROM SHHG emission [6, 31] and we will in the following consider the experimentally observed SHHG emission as such its photon energy range is below the coherent wake emission (CWE) spectral cutoff

Summary

Introduction

Surface high-harmonic generation (SHHG) from relativistic plasma mirrors has long been recognized as an efficient route to high-energy intense attosecond XUV pulses [1,2,3]. Plasma mirrors complement the established attosecond pulse generation method via high-harmonic generation (HHG) in gases at much lower intensities in the strong-field regime, since they exhibit no inherent limitation for the driving intensity. They allow full exploitation of ultra-high intensity lasers in order to convert an extremely large number of photons from a femtosecond laser into attosecond XUV pulses. The laser-to-XUV conversion efficiencies of ~ 10−4 currently experimentally observed for plasma mirrors with a0~ 1 [3, 8,9,10] already rival the highest demonstrated efficiencies of gas HHG [11, 12] This makes SHHG on plasma mirrors one of the paramount candidates for greatly enhancing the available energy of attosecond XUV pulses

Methods

Findings

Discussion

Conclusion