Water-Window X-Ray Pulses from a Laser-Plasma Driven Undulator (original) (raw)
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An ultracompact X-ray source based on a laser-plasma undulator
Nature Communications, 2014
The capability of plasmas to sustain ultrahigh electric fields has attracted considerable interest over the last decades and has given rise to laser-plasma engineering. Today, plasmas are commonly used for accelerating and collimating relativistic electrons, or to manipulate intense laser pulses. Here we propose an ultracompact plasma undulator that combines plasma technology and nanoengineering. When coupled with a laser-plasma accelerator, this undulator constitutes a millimetre-sized synchrotron radiation source of X-rays. The undulator consists of an array of nanowires, which are ionized by the laser pulse exiting from the accelerator. The strong charge-separation field, arising around the wires, efficiently wiggles the laser-accelerated electrons. We demonstrate that this system can produce bright, collimated and tunable beams of photons with 10-100 keV energies. This concept opens a path towards a new generation of compact synchrotron sources based on nanostructured plasmas.
Efficient picosecond x-ray pulse generation from plasmas in the radiation dominated regime
Optica
The efficient conversion of optical laser light into bright ultrafast x-ray pulses in laser created plasmas is of high interest for dense plasma physics studies, material science, and other fields. However, the rapid hydrodynamic expansion that cools hot plasmas has limited the x-ray conversion efficiency (CE) to 1% or less. Here we demonstrate more than one order of magnitude increase in picosecond x-ray CE by tailoring near solid density plasmas to achieve a large radiative to hydrodynamic energy loss rate ratio, leading into a radiation loss dominated plasma regime. A record 20% CE into hν > 1 keV photons was measured in arrays of large aspect ratio Au nanowires heated to keV temperatures with ultrahigh contrast femtosecond laser pulses of relativistic intensity. The potential of these bright ultrafast x-ray point sources for table-top imaging is illustrated with single shot flash radiographs obtained using low laser pulse energy. These results will enable the deployment of brighter laser driven x-ray sources at both compact and large laser facilities.
Observation of Plasma-Undulator Harmonics from a Laser Wakefield Accelerator
2009
X-rays pulses with undulator-like spectra are observed from a laser-wakefield accelerator. The observation of characteristic undulator features, with well separated harmonic peaks, required measuring the x-ray spectra of individual x-ray pulses. Electrons were accelerated in gas-filled dielectric capillary tubes at laser intensities as low as I = (6 ± 3) × 10 17 W/cm 2. Far-field images of the x-rays, in combination with numerical simulations of collective trajectories of the electrons, provide insight into the interaction.
Progress toward a laser-driven x-ray free-electron laser
SPIE Newsroom, 2009
The use of x-ray radiation has driven the development of synchrotron sources and, more recently, x-ray free-electron lasers (FELs). These microwave-based facilities are huge and expensive, yet governments are prepared to support them (usually one per nation) because of their great value to industry, academia, and society. However, laser-wakefield accelerators (LWFAs) are now advancing to the point where compact radiation sources could be developed into a new, complementary, or even disruptive technology. In addition to reductions in scale and cost-by a factor of up to 1000-x-ray pulse durations are significantly shorter than those of conventional lasers, which could facilitate probing of ultrafast dynamic processes. The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) project, based at the University of Strathclyde, is developing laser-plasma accelerators as drivers of radiation sources. 1 The first demonstration of a compact synchrotron source based on an LWFA was recently demonstrated using a conventional undulator and a diverging electron beam. 2 Our challenge is to develop a compact x-ray FEL. Here we focus on developments to improve the electron-beam properties and discuss the suitability of LWFAs as drivers of FELs. Our work shows that the once-distant prospect of a compact x-ray FEL is now within reach. On the ALPHA-X accelerator beam line (see Figure 1), electrons are accelerated in a relativistically self-guiding plasma channel formed in a hydrogen-gas jet by a 35fs titaniumsapphire laser pulse with a power of 1J. Electrons are selfinjected from the background plasma into the density wake that trails behind the laser pulse (through the combined action
Generation of femtosecond X-ray pulses via laser–electron beam interaction
Applied Physics B, 2000
The generation of femtosecond X-ray pulses will have important scientific applications by enabling the direct measurement of atomic motion and structural dynamics in condensed matter on the fundamental time scale of a vibrational period. Interaction of femtosecond laser pulses with relativistic electron beams is an effective approach to generating femtosecond pulses of X-rays. In this paper we present recent results from proof-of-principle experiments in which 300 fs pulses are generated from a synchrotron storage ring by using an ultrashort optical pulse to create femtosecond time structure on the stored electron bunch. A previously demonstrated approach for generating femtosecond X-rays via Thomson scattering between terawatt laser pulses and relativistic electrons is reviewed and compared with storage-ring based schemes.
Ultrafast X-ray pulse characterization at free-electron lasers
Nature Photonics, 2012
The ability to fully characterize ultrashort, ultra-intense X-ray pulses at free-electron lasers (FELs) will be crucial in experiments ranging from single-molecule imaging to extreme-timescale X-ray science. This issue is especially important at current-generation FELs, which are primarily based on self-amplified spontaneous emission and radiate with parameters that fluctuate strongly from pulse to pulse. Using single-cycle terahertz pulses from an optical laser, we have extended the streaking techniques of attosecond metrology to measure the temporal profile of individual FEL pulses with 5 fs full-width at half-maximum accuracy, as well as their arrival on a time base synchronized to the external laser to within 6 fs r.m.s. Optical laser-driven terahertz streaking can be utilized at any X-ray photon energy and is non-invasive, allowing it to be incorporated into any pump-probe experiment, eventually characterizing pulses before and after interaction with most sample environments.
Petawatt, picosecond laser pulses offer rich opportunities in generating synchrotron x-rays. This paper concentrates on the regimes accessible with the PETAL laser, which is a part of the Laser Megajoule (LMJ) facility. We explore two physically distinct scenarios through Particle-in-Cell simulations. The first one realizes in a dense plasma, such that the period of electron Langmuir oscillations is much shorter than the pulse duration. Hallmarks of this regime are longitudinal breakup (" self-modulation ") of the picosecond-scale laser pulse and excitation of a rapidly evolving broken plasma wake. It is found that electron beams with a charge of several tens of nC can be obtained, with a quasi-Maxwellian energy distribution extending to a few-GeV level. In the second scenario, at lower plasma densities, the pulse is shorter than the electron plasma period. The pulse blows out plasma electrons, creating a single accelerating cavity, while injection on the density downramp creates a nC quasi-monoenergetic electron bunch within the cavity. This bunch accelerates without degradation beyond 1 GeV. The x-ray sources in the self-modulated regime offer a high number of photons (∼10^12) with the slowly decaying energy spectra extending beyond 60 keV. In turn, quasimonoenergetic character of the electron beam in the blowout regime results in the synchrotron-like spectra with the critical energy around 10 MeV and a number of photons > 10^9. Yet, much smaller source duration and transverse size increase the x-ray brilliance by more than an order of magnitude against the self-modulated case, also favoring high spatial and temporal resolution in x-ray imaging. In all explored cases, accelerated electrons emit synchrotron x-rays of high brilliance, B > 10^20 photons/s/mm^2/mrad^2/0.1%BW. Synchrotron sources driven by picosecond kilojoule lasers may thus find an application in x-ray diagnostics on such facilities such as the LMJ or National Ignition Facility (NIF).
Journal of the Optical Society of America B, 1996
The feasibility of using thin, freely suspended films as a target in femtosecond laser-produced plasma (FLP) experiments is discussed. The conditions for producing a significant increase in the FLP temperature (as much as a few kilo-electron-volts) are determined by use of a simple numerical code. An increase in temperature leads to an increase in x-ray yield as well as to a shift of the x-ray spectrum toward shorter wavelengths. The experimental results on soft-x-ray generation from FLP on resonance lines of highly stripped hydrogenlike and heliumlike boron ions are supported by results obtained with this code. FLP is also analyzed as a source of soft x-rays, particularly in the 2-4-nm region (the so-called water window).