Femtosecond x rays from laser-plasma accelerators (1301.5066v1)

Abstract: Relativistic interaction of short-pulse lasers with underdense plasmas has recently led to the emergence of a novel generation of femtosecond x-ray sources. Based on radiation from electrons accelerated in plasma, these sources have the common properties to be compact and to deliver collimated, incoherent and femtosecond radiation. In this article we review, within a unified formalism, the betatron radiation of trapped and accelerated electrons in the so-called bubble regime, the synchrotron radiation of laser-accelerated electrons in usual meter-scale undulators, the nonlinear Thomson scattering from relativistic electrons oscillating in an intense laser field, and the Thomson backscattered radiation of a laser beam by laser-accelerated electrons. The underlying physics is presented using ideal models, the relevant parameters are defined, and analytical expressions providing the features of the sources are given. Numerical simulations and a summary of recent experimental results on the different mechanisms are also presented. Each section ends with the foreseen development of each scheme. Finally, one of the most promising applications of laser-plasma accelerators is discussed: the realization of a compact free-electron laser in the x-ray range of the spectrum. In the conclusion, the relevant parameters characterizing each sources are summarized. Considering typical laser-plasma interaction parameters obtained with currently available lasers, examples of the source features are given. The sources are then compared to each other in order to define their field of applications.

• The paper demonstrates that laser-plasma interactions can generate femtosecond x-rays with high brightness through mechanisms like betatron radiation and Thomson backscattering.
• It details various methodologies including synchrotron radiation in undulators and nonlinear Thomson scattering, supported by experimental data and numerical estimates.
• It underscores the promise of these sources for ultrafast imaging and compact x-ray free-electron lasers, fostering advancements in high-energy photon science.

Overview of "Femtosecond x rays from laser-plasma accelerators"

The paper "Femtosecond x rays from laser-plasma accelerators" by S. Corde et al. provides a comprehensive review of x-ray generation using laser-plasma interactions. This research leverages the relativistic interaction of short-pulse lasers with underdense plasmas, resulting in innovative femtosecond x-ray sources. The authors categorize the mechanisms into several theoretical frameworks and provide insights into the associated physics, recent advancements, and potential future developments.

Key Mechanisms Discussed

The paper evaluates four major radiation mechanisms:

1. Betatron Radiation: This occurs as electrons accelerate in the plasma bubble regime, where they follow wiggling trajectories due to the bubble's transverse electric fields, resulting in synchrotron-like emission. The paper highlights the source's high brightness and femtosecond duration, which are promising for ultra-fast imaging applications.
2. Synchrotron Radiation in Conventional Undulators: Here, laser-plasma accelerators feed electron beams into conventional undulators, emitting x-rays. The authors discuss the technical challenges related to electron transport and phase space matching, necessary to achieve high coherence and brightness.
3. Nonlinear Thomson Scattering: Nonlinear Thomson scattering is explored with electrons oscillating in high-intensity laser fields. The paper analytically models electron trajectories and radiation outputs, emphasizing the mechanism's potential for producing high photon flux directly by laser interaction without complex acceleration setups.
4. Thomson Backscattering: This involves scattering a counterpropagating laser off relativistic electrons, yielding high-energy radiation due to double Doppler shifts. The authors explore the conditions required for efficient frequency upconversion in the backscattering process.

Numerical Results and Experimental Review

The paper provides numerical estimations for each mechanism, including photon numbers, energies achievable, and x-ray beam divergences. Additionally, the practical execution of these theoretical models is backed by experimental data. For instance, betatron radiation has been demonstrated up to tens of keV photon energies with divergences in the order of tens of milliradians, while Thomson backscattering experiments have yielded photon energies in the gamma-ray range with substantial brightness.

Implications and Future Prospects

The research in this paper underscores the promise of femtosecond x-ray and gamma-ray sources for advancing imaging techniques, including medical radiography and materials science applications. These sources offer novel possibilities for probing matter at atomic scales with high temporal resolution, thus opening new frontiers in fundamental science and industry.

One notable aspect is the potential application of laser-plasma accelerators to drive compact x-ray Free-Electron Lasers (FELs). By melding large-scale accelerator physics with laser-based technologies, the prospect of more accessible and widely distributed FEL facilities becomes conceivable.

Conclusion

The authors effectively convey the complex dynamics of laser-plasma interaction and radiation emission. Future research as indicated by the authors is directed towards enhancing the stability and controllability of these sources, as well as achieving coherent radiation through laser-plasma-driven FELs. Their work provides a solid foundation for ongoing advancements in laser technology and plasma physics, with the possibility of tangible applications in high-energy photon sciences.