Due to their short wavelength, X-rays can in principle be focused down to a few nanometres and below. At the same time, it is this short wavelength that puts stringent requirements on X-ray optics and their metrology. Both are limited by today's technology. In this work, we present accurate at wavelength measurements of residual aberrations of a refractive X-ray lens using ptychography to manufacture a corrective phase plate. Together with the fitted phase plate the optics shows diffraction-limited performance, generating a nearly Gaussian beam profile with a Strehl ratio above 0.8. This scheme can be applied to any other focusing optics, thus solving the X-ray optical problem at synchrotron radiation sources and X-ray free-electron lasers.
Harmonic generation in the limit of ultra-steep density gradients is studied experimentally. Observations demonstrate that while the efficient generation of high order harmonics from relativistic surfaces requires steep plasma density scale-lengths (Lp/λ < 1) the absolute efficiency of the harmonics declines for the steepest plasma density scale-length Lp → 0, thus demonstrating that near-steplike density gradients can be achieved for interactions using high-contrast high-intensity laser pulses. Absolute photon yields are obtained using a calibrated detection system. The efficiency of harmonics reflected from the laser driven plasma surface via the Relativistic Oscillating Mirror (ROM) was estimated to be in the range of 10 −4 − 10 −6 of the laser pulse energy for photon energies ranging from 20 − 40 eV, with the best results being obtained for an intermediate density scale-length.PACS numbers: 52.59.Ye, 52.38.-r Keywords: surface high-harmonic generation, relativistic laser plasma interaction, attosecond pulse generation Ultrashort XUV pulses are a promising tool for a wide range of applications including attosecond laser physics and seeding of free-electron X-ray lasers. Typically, they are created by the nonlinear frequency up-conversion of an intense femtosecond driving laser field in a gaseous medium. Remarkable progress has been made to the present date with efficiencies reaching the level of 10 −4 at 20 nm wavelengths [1,2]. Such efficiencies are not yet available at shorter wavelengths or for attosecond pulse generation and the low intensities at which harmonic conversion takes place in gaseous media, makes harnessing the high peak power in the 0.1−1PW regime challenging. High-harmonic generation at a sharp plasma-vacuum interface via the Relativistically Oscillating Mirror (ROM) mechanism [3] is predicted to overcome these limitations and result in attosecond pulses of extreme peak power [4,5].While other mechanisms such as Coherent Wake Emission (CWE) can also emit XUV harmonics [6], the ROM mechanism is generally reported to dominate in the limit of highly relativistic intensities, where the normalized vector potential a 2 0 = Iλ 2 /(1.37 · 10 18 µm 2 W/cm 2 ) 1. The efficiency of ROM harmonics is predicted to converge to a power law for ultra-relativistic intensities [7], such that the conversion efficiency is given by η ≈ (ω/ω 0 ) −8/3 up to a threshold frequency ω t ∼ γ 3 , beyond which the spectrum decays exponentially. Here, γ is the maximum value of the Lorentz-factor associated with the reflection point of the ROM process. While these predictions correspond well with the observations made in experiments using pulse durations of the order of picoseconds in terms of highest photon energy up to keV [8,9] and the slope of the harmonic efficiency [10], no absolute efficiency measurements have been reported to date.The plasma density scale-length plays a critical role in determining the response of the plasma to the incident laser radiation. In the picosecond regime, the balance between the laser pre...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.