Tunable Isolated Attosecond X-ray Pulses with Gigawatt Peak Power from a Free-Electron Laser (1906.10649v1)

Abstract: The quantum mechanical motion of electrons in molecules and solids occurs on the sub-femtosecond timescale. Consequently, the study of ultrafast electronic phenomena requires the generation of laser pulses shorter than 1 fs and of sufficient intensity to interact with their target with high probability. Probing these dynamics with atomic-site specificity requires the extension of sub-femtosecond pulses to the soft X-ray spectral region. Here we report the generation of isolated GW-scale soft X-ray attosecond pulses with an X-ray free-electron laser. Our source has a pulse energy that is six orders of magnitude larger than any other source of isolated attosecond pulses in the soft X-ray spectral region, with a peak power in the tens of gigawatts. This unique combination of high intensity, high photon energy and short pulse duration enables the investigation of electron dynamics with X-ray non-linear spectroscopy and single-particle imaging.

• The paper reports isolated attosecond X-ray pulses with gigawatt peak power using a free-electron laser, opening new avenues for ultrafast electron dynamics research.
• It employs an enhanced self-amplified spontaneous emission technique to produce soft X-ray pulses with energies six orders of magnitude higher than previous methods.
• Single-shot pulse diagnostics and a two-color pulse scheme enable precise pump-probe experiments and advanced time-resolved X-ray imaging.

Tunable Isolated Attosecond X-ray Pulses with Gigawatt Peak Power from a Free-Electron Laser

The paper discusses an advancement in the field of attosecond science, particularly in generating isolated attosecond X-ray pulses using a free-electron laser (FEL). The paper demonstrates production of high-energy pulses with gigawatt peak power, potentially enabling significant progress in ultrafast spectroscopy and imaging.

Key Contributions

1. Generation of Isolated Attosecond Pulses: The paper achieves a notable milestone in generating isolated attosecond pulses with gigawatt-scale peak power. This breakthrough is essential for studying ultrafast electronic phenomena with high spatial and temporal resolution.
2. Improving Intensity and Photon Energy: The reported source vastly surpasses previous sources in terms of pulse energy by six orders of magnitude for isolated attosecond pulses in the soft X-ray range. The peak power of the source reaches tens to hundreds of gigawatts.
3. Enhanced Self-Amplified Spontaneous Emission (ESASE): The research utilizes an enhanced self-amplified spontaneous emission technique to overcome the bandwidth limitations of conventional XFELs. By modulating and compressing the electron beam, the setup allows the generation of sub-femtosecond X-ray pulses.
4. Single-Shot Pulse Diagnostics: Employing an attosecond streak camera, the paper achieves temporal characterization of individual pulses, determining a median pulse duration of approximately 284 attoseconds at 905 eV and 476 attoseconds at 570 eV.
5. Two-Color Scheme for Pump-Probe Experiments: The paper also explores the generation of synchronized two-color pulse pairs, suitable for advanced pump-probe experiments. By implementing a split undulator technique, the paper offers a method to control the delay and energy separation between pulses.

Implications

The production of intense, tunable attosecond X-ray pulses with such high peak power significantly advances the tools available for exploring ultrafast electron dynamics. Applications in nonlinear X-ray spectroscopy, attosecond pump-probe experiments, and single-shot X-ray imaging are conceivable.

The capability to generate two-color pulses with distinct photon energies opens possibilities for targeted excitation and probing of electronic dynamics in molecular systems at atomic-site specificity. This development supports the enhancement of multidimensional spectroscopic applications.

Future Directions

The capacity for frequency tuning and scalability to MHz repetition rates with monitoring and diagnostics emphasizes FEL sources' potential to revolutionize time-resolved X-ray science. Future research could further explore optimizing the pulse energy and temporal control in pump-probe setups.

Moreover, leveraging FEL facilities like the upcoming LCLS-II upgrade, facilitating continuous tuning across extensive energy ranges, might extend the reach of attosecond spectroscopy to broader applications in chemistry, biology, and materials science. The combination of high photon flux and rapid tunability positions this technology as a pivotal tool in attosecond science.