arXiv subjects

Yaozong Xiao

Publications and source records attributed to Yaozong Xiao.

4 recordsLinked to original sources

arXiv2026

Fully coherent short wavelength free-electron laser driven by a single sub-microjoule seed

High-repetition-rate, fully coherent extreme-ultraviolet (EUV) and X-ray free-electron lasers (FELs) are essential for advanced time-resolved ultrafast spectroscopies. While external seeding serves as the standard technique to achieve precise temporal coherence, conventional methods demand hundred-megawatt peak-power laser systems. Furthermore, advanced configurations like echo-enabled harmonic generation (EEHG) introduce the severe complexities of dual-laser synchronization. Together, these requirements fundamentally restrict operations to kilohertz repetition rates and compromise overall system stability. Here, we experimentally demonstrate a fully coherent EEHG-FEL driven by a single, sub-microjoule seed laser. By employing a direct-amplification enabled harmonic generation technique, we utilize an initial 0.4 microJ (2 MW peak power) ultraviolet seed to directly drive coherent lasing at nanometer wavelengths. By eliminating the need for extreme peak powers and multiple synchronized lasers, this approach significantly simplifies the seeding architecture and provides a practical and robust pathway toward megahertz-class, fully coherent EUV and X-ray light sources.

physics.acc-ph↗

arXiv2025

First Lasing and Stable Operation of a Direct-Amplification Enabled Harmonic Generation Free-Electron laser

Seeded free-electron lasers (FELs) capable of operating at repetition rates up to the MHz level are in high demand for advanced time-resolved spectroscopies, which require both full longitudinal coherence and high average photon flux in the extreme ultraviolet (EUV) and x-ray regimes. However, conventional external-seed laser systems cannot sustain MHz operation with sufficient hundreds of megawatts peak power requirement due to their limited total power. Here, we report the first lasing and stable operation of a direct-amplification-enabled harmonic generation FEL driven by a weak seed laser with MW-level peak power. Beginning with an ultraviolet seed laser with only 0.75 μJ pulse energy, we demonstrate its direct amplification to over 10 μJ within an 8-meter-long modulator. We observe coherent harmonic generation up to the 12th harmonic of the seed and achieve saturation of the 7th harmonic in the radiator. These results represent a crucial milestone toward the realization of MHz-class, fully coherent EUV and x-ray light sources.

physics.acc-ph↗

arXiv2025

Isolated attosecond free-electron laser based on a sub-cycle driver from hollow capillary fibers

The attosecond light source provides an advanced tool for investigating electron motion using time-resolved-spectroscopy techniques. Isolated attosecond pulses, especially, will significantly advance the study of electron dynamics. However, achieving high-intensity isolated attosecond pulses is still challenging at the present stage. In this paper, we propose a novel scheme for generating high-intensity, isolated attosecond soft X-ray free-electron lasers (FELs) using a mid-infrared (MIR) sub-cycle modulation laser from gas-filled hollow capillary fibers (HCFs). The multi-cycle MIR pulses are first compressed to sub-cycle using a helium-filled HCF with decreasing pressure gradient due to soliton self-compression effect. By utilizing such sub-cycle MIR laser pulse to modulate the electron beam, we can obtain a quasi-isolated current peak, which can then produce an isolated FEL pulse with high signal-to-noise ratio (SNR), naturally synchronizing with the sub-cycle MIR laser pulse. Numerical simulations have been carried out, including the sub-cycle pulse generation, electron beam modulation and FEL radiation processes. The simulation results indicate that an isolated attosecond pulse with wavelength of 1 nm, peak power of ~28 GW, pulse duration of ~600 attoseconds and SNR of ~96.4% can be generated by our proposed method. The numerical results demonstrated here pave a new way for generating the high-intensity isolated attosecond soft X-ray pulse, which may have many applications in nonlinear spectroscopy and atomic-site electronic process.

physics.acc-ph↗

arXiv2023

Self-referenced Spectral Interferometry for Single-shot Characterization of Ultrashort Free-electron Laser Pulses

Attosecond x-ray pulse with known spectro-temporal information is an essential tool for the investigation of ultrafast electron dynamics in quantum systems. Ultrafast free-electron lasers (FELs) have the unique advantage on unprecedented high-intensity at x-ray wavelengths. However, no suitable method has been established so far for the spectro-temporal characterization of these ultrashort x-ray pulses. In this letter, a simple method has been proposed based on self-referenced spectral interferometry for reconstructing ultrashort FEL pulses both in temporal and spectral domains. We have demonstrated that the proposed method is reliable to reconstruct the temporal profile and phase of attosecond x-ray FEL pulses with an error of only a few-percent-level. Moreover, the first proof-of-principle experiment has been performed to achieve single-shot spectro-temporal characterization of ultrashort pulses from a high-gain FEL. The precision of the proposed method will be enhanced with the decrease of the pulse duration, paving a new way for complete attosecond pulse characterization at x-ray FELs.

physics.acc-ph↗