Single XUV pulse generation via waveform-controlled laser-plasma interaction
image: Fig. 1. Influence of the drive pulse temporal envelope and its waveform on the formation of the electron mirror and backscattered signal. The 40-nm-thick plasma slab (located from 6휆L to 6.05휆L ) is irradiated by drive pulses possessing different waveforms and temporal envelopes, (A) top-hat, (B) Gaussian, and (C) optimal dual-color Gaussian (with P = 0.4) pulses, which causes various temporal evolutions of electron number density. In all cases, the drive beam propagates from left to right and is incident normally on the 40-nm-thick pre-ionized plasma foil at 6TL . (D) compares the temporal waveforms of the single- (1휔) and 2-color (1휔 + 2휔) drive Gaussian pulses with end-to-end 12TL temporal duration and polarization along the y-direction. The inset at the lower left hand side enlarges the waveforms from 4TL to 5TL , highlighting the steepness of the accelerating 2-color field. The counterpropagating source pulse with a duration of 6TL and a peak amplitude of a0 = 0.1 interacts with the electron sheet and reflects partially. The squared field of the normalized Thomson backscattering (TBS) signals are shown in (E), indicating the generation of a single 110-as pulse (in the full width at half-maximum [FWHM]) in the case of a ( 1휔+2휔 ) drive beam. The duration of the TBS signal, resulting from interaction with the produced relativistic electron sheet (RES) in panel (A) is 380 as. This pulse is scaled by a factor of 10 (in blue). The reflected pulses are temporally shifted for better comparison. The corresponding frequency spectra of the TBS radiations are illustrated in panel (F). The attosecond pulse (AP) generated by the interaction of the dual-color drive beam and foil target is composed of a spectrum peaking at 26휔L .
Credit: Ultrafast Science
Researchers propose a novel scheme to produce isolated attosecond pulses using relativistic electron mirrors, paving the way for next-generation ultrafast spectroscopy.
Capturing nature’s fastest phenomena has long pushed the boundaries of physics. Among the most intriguing concepts is the reflection of light from mirrors moving at relativistic speeds—a notion first introduced by Einstein over a century ago, yet still vibrant with scientific potential. Creating and controlling these so-called relativistic electron mirrors remains a formidable challenge, despite remarkable advances in high-intensity, ultrashort-pulse laser technology. When successfully generated, these mirrors can compress an incoming femtosecond laser pulse into an ultra-intense extreme ultraviolet (XUV) attosecond burst, opening the door to groundbreaking applications in ultrafast science, high-resolution imaging, and attosecond spectroscopy.
An international team of researchers from ELI ALPS in Hungary and Pasqal in France, have computationally demonstrated a new, robust and tunable scheme for generating isolated attosecond pulses in the extreme ultraviolet (XUV) regime through relativistic laser-plasma interaction. The new approach employs coherent Thomson backscattering from a single dense relativistic electron sheet (RES), created when a waveform-controlled laser interacts with an ultrathin plasma foil. Unlike traditional single color Gaussian laser pulses that typically produce multiple electron layers and compromise coherence, this technique uses two-color waveform synthesis- combining a fundamental frequency with its second harmonic- to sculpt the laser field precisely. As a result, a single, dense, nanometer-scale electron sheet can be generated that acts as a relativistic mirror. When a counter-propagating few-cycle pulse reflects off this mirror, it compresses into an intense attosecond burst. The detailed findings have been published recently in the journal Ultrafast Science.
Key Results showcase a typical pulse Duration of 110 attoseconds (FWHM) attaining a spectral up-shift of up to 26× the fundamental frequency and a peak intensity enhancement >10× compared to conventional schemes. In addition, the method promises robustness which is tolerant to typical experimental noise and timing jitter.
This innovation proposes a feasible experimental approach based on relativistic laser plasma science. With the rapid enhancement in laser technology such approach promises transformative applications in ultrafast spectroscopy, solid-state physics, and high-field science.
The research team consisted of Mojtaba Shirozhan, a PhD student at ELI ALPS; Dr. Fabien Quéré working as Lead Academic and R&D partnerships at Pasqal and Director of the IOGS-CNRS-Pasqal Joint Lab and Dr. Subhendu Kahaly, Leading Scientist and the Head of Secondary Sources Division at ELI ALPS.