Diffraction-limited coherent wake emission

E Porat,I Cohen,A Levanon,I Pomerantz,H Yehuda

doi:10.1103/physrevresearch.3.l032059

E Porat, I Cohen + Show 3 more

Open Access

https://doi.org/10.1103/physrevresearch.3.l032059

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Abstract

The plasma mirror is a relativistic optical element that under certain irradiation conditions generates intense attosecond extreme-ultraviolet light pulses, in a process known as coherent wake emission (CWE). CWE has been previously characterized by its high spatial divergence, originating from an intrinsic intensity-dependent phase accumulation. In this Letter, we show that the transverse variations of the plasma expansion can completely cancel the CWE intrinsic phase. Accordingly, we experimentally demonstrate nearly diffraction-limited CWE with unprecedented divergence, under 6 mrad. We validate our analytical model with particle in cell simulations. This understanding facilitates the development of plasma mirrors as applicable ultraviolet light sources.Received 9 March 2021Accepted 5 August 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.L032059Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHigh intensity laser-plasma interactionsHigh-order harmonic generationPhysical SystemsRelativistic plasmasAtomic, Molecular & OpticalPlasma Physics

Highlights

Chirped-pulse amplification (CPA) technology made possible the realization of intense laser fields, in which oscillating electrons reach nearly the speed of light
plasma mirror (PM) present highly nonlinear laser-plasma dynamics, manifested by the generation of synchronized attosecond light [5] and electron bursts [6]. These are of great interest to ultrafast science, because the availability of ultrashort, coherent pulses in the extreme-ultraviolet (XUV) region is a prerequisite for many applications, such as attosecond spectroscopy [7], biological imaging [8], and material sciences [9]
The XUV emission manifests in a discrete harmonic spectrum of the fundamental laser wavelength. These so-called surface harmonics have been established to originate from distinct types of plasma dynamics, divided into two regimes of laser intensity: relativistic processes driven by ultrahigh intensities of over 1019 W cm−2, such as the relativistic oscillating mirror [10] and coherent

Summary

Published by the American Physical Society

Our model, in which CWE beams are controlled to become highly collimated, with nearly diffraction limited divergence. To model the local plasma expansion across the focal spot, we determine the plasma scale length by time integrating the plasma velocity until the peak of the pulse (at t = 0): L(r, 0) =. Where η is the radial intensity distribution of a spot with radius wL; P is the temporal evolution of the main pulse with duration τL, e.g., a Gaussian; 1 is the amplitude of the pedestal normalized at t = 0; and τp > τL is its time constant. The substitution of Eq (2) separates Eq (1) into two parts, for the main pulse and the pedestal, that can be solved separately. We assume the plasma expansion initiates during the pedestal phase, having ti τL.

Hmax cos θ

Findings

TL aλ sin θ