All-optical Compton gamma-ray source

Abstract: One of the major goals of research for laser-plasma accelerators is the realization of compact sources of femtosecond X-rays. In particular, using the modest electron energies obtained with existing laser systems, Compton scattering a photon beam off a relativistic electron bunch has been proposed as a source of high-energy and high-brightness photons. However, laser-plasma based approaches to Compton scattering have not, to date, produced X-rays above 1 keV. Here, we present a simple and compact scheme for a Compton source based on the combination of a laser-plasma accelerator and a plasma mirror. This approach is used to produce a broadband spectrum of X-rays extending up to hundreds of keV and with a 10,000-fold increase in brightness over Compton X-ray sources based on conventional accelerators. We anticipate that this technique will lead to compact, high-repetition-rate sources of ultrafast (femtosecond), tunable (X- through gamma-ray) and low-divergence (~1 degree) photons from source sizes on the order of a micrometre.

• The paper introduces an innovative method using laser-plasma accelerators and plasma mirrors to achieve efficient Compton scattering that produces broadband X-rays up to several hundred keV.
• The approach attains a brightness increase nearing 10,000 times over conventional sources by exploiting femtosecond lasers and a compact, high-repetition design.
• Experimental validation combined with test particle simulations confirms the system's potential for advanced imaging and scalable laser-plasma applications.

An Overview of the All-Optical Compton Gamma-Ray Source

The paper explores a novel and efficient method for creating a broadband source of high-energy X-rays through an all-optical Compton gamma-ray technique. This approach capitalizes on the characteristics and capabilities of laser-plasma accelerators, combined with plasma mirrors, to produce a high-brightness X-ray output, significantly surpassing traditional Compton X-ray sources.

Key Contributions and Findings

1. Innovative Utilization of Laser-Plasma Accelerators: The primary mechanism involves a laser-plasma accelerator, where a powerful femtosecond laser pulse generates a relativistic electron bunch in a gas jet. This same laser pulse is reflected off a plasma mirror, which is a crucial element in this setup. The plasma mirror not only reflects the laser pulse but ensures temporal and spatial overlap with the electron bunch, facilitating efficient Compton scattering.
2. Broadband X-ray Production: The method produces X-ray radiation extending up to several hundred keV with an exceptionally high brightness, achieving a reported increase of approximately 10,000 times over conventional Compton X-ray sources. This is attributed to the small source size and femtosecond-scale pulse duration intrinsic to the optical scheme.
3. Compact and High-Repetition Rate Potential: The described technology is compact, relying solely on a single laser system. This simplification paves the way for feasible deployment in settings where space and resources are constrained while allowing for high repetition rates due to its design.
4. Experimental Validation: The work includes detailed experimental setups and diagnostics validating the capabilities of the system, including the use of copper filters to measure X-ray spectrum and radiography to showcase imaging capability. A knife-edge technique is used to quantify the source size, affirming values under 3 micrometers.
5. Numerical and Theoretical Underpinning: Complementing experimental findings, the authors employ test particle simulations to model electron trajectories and resulting radiation, providing numerically corroborated results regarding the energy distribution and intensity of the X-ray emission.

Implications and Future Directions

• Impact on Imaging and Analysis: The capability of producing high-energy photon beams with narrow divergence and small source size opens new avenues in imaging, particularly for examining dense materials and conducting phase contrast imaging.
• Advancements in Laser-Plasma Technology: By demonstrating the practicality of utilizing high-energy laser systems to produce scalable and tunable X-ray sources, the paper contributes to the broader field of laser-plasma interactions and accelerators, providing a foundational method applicable to various scientific and industrial applications.
• Prospects for Enhanced Sources: The technique could evolve towards creating monoenergetic X-ray sources through refinement of electron injection and post-acceleration methods, an area ripe for further exploration, potentially with advancements in laser modulation and control strategies.
• Potential for Broader Integration: With further development, this technique could integrate into various high-energy physics experiments, non-destructive testing in industry, and even medical imaging, contingent on scale-up and regulatory compliance in medical settings.

In conclusion, this paper details a remarkably effective method for generating high-energy X-rays leveraging a laser-plasma accelerator setup. The approach is distinguished by its simplicity, efficiency, and the ability to yield high-brightness X-ray beams, offering considerable promise for advancing X-ray-based imaging and analysis technologies. The methodology, while experimental, is theoretically robust and indicates significant potential for diversification in both applications and enhancements of X-ray generation.