Energy-scalable single-burst attosecond emission at kiloelectronvolt photon energies
Abstract
Attosecond soft-X-ray pulses at kiloelectronvolt photon energies would provide direct access to the L-edges of transition metals, enabling element-specific studies of charge, spin, and orbital dynamics on their intrinsic timescales. However, attosecond emission in this spectral region has remained elusive because the only phase-matched keV high-harmonic source demonstrated to date employed multicycle driving pulses without carrier-envelope-phase (CEP) control. A long-standing gap has therefore persisted between keV photon energies and CEP-controlled attosecond emission. Here, we bridge this gap using a CEP-stabilized mid-infrared laser system with pulse durations tunable to the sub-cycle regime. Through phase-matched highharmonic generation in low-pressure neutral helium under meter-scale loose-focusing conditions, we generate coherent soft-X-ray continua reaching 1.2 keV. Crucially, we observe CEP-dependent spectral modulation that reaches into the transition-metal L-edge region, providing experimental evidence consistent with the generation of isolated attosecond pulses. To demonstrate the capabilities of our source, we perform broadband soft-X-ray absorption spectroscopy spanning the Ti, Fe, Co, and Ni L-edges, as well as the O K-edge, and resolve near-edge fine structures. By combining meter-scale loose focusing with low-pressure phase matching, our approach addresses key energy-scaling limitations of previous keV high-harmonic sources and establishes a phase-matched, CEP-controlled keV soft-X-ray platform for attosecond spectroscopy of magnetic, quantum, and strongly correlated materials.
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BibTeX
@misc{nishimiya2026energyscalable,
title = {{Energy-scalable single-burst attosecond emission at kiloelectronvolt photon energies}},
author = {Kaito Nishimiya and Eiji J. Takahashi},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.06454},
eprint = {2609.06454},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.06454},
}
RIS
TY - UNPB
TI - Energy-scalable single-burst attosecond emission at kiloelectronvolt photon energies
AU - Kaito Nishimiya
AU - Eiji J. Takahashi
PY - 2026
DA - 2026/09/06
PB - arXiv
DO - 10.48550/arxiv.2609.06454
UR - https://arxiv.org/abs/2609.06454
AB - Attosecond soft-X-ray pulses at kiloelectronvolt photon energies would provide direct access to the L-edges of transition metals, enabling element-specific studies of charge, spin, and orbital dynamics on their intrinsic timescales. However, attosecond emission in this spectral region has remained elusive because the only phase-matched keV high-harmonic source demonstrated to date employed multicycle driving pulses without carrier-envelope-phase (CEP) control. A long-standing gap has therefore persisted between keV photon energies and CEP-controlled attosecond emission. Here, we bridge this gap using a CEP-stabilized mid-infrared laser system with pulse durations tunable to the sub-cycle regime. Through phase-matched highharmonic generation in low-pressure neutral helium under meter-scale loose-focusing conditions, we generate coherent soft-X-ray continua reaching 1.2 keV. Crucially, we observe CEP-dependent spectral modulation that reaches into the transition-metal L-edge region, providing experimental evidence consistent with the generation of isolated attosecond pulses. To demonstrate the capabilities of our source, we perform broadband soft-X-ray absorption spectroscopy spanning the Ti, Fe, Co, and Ni L-edges, as well as the O K-edge, and resolve near-edge fine structures. By combining meter-scale loose focusing with low-pressure phase matching, our approach addresses key energy-scaling limitations of previous keV high-harmonic sources and establishes a phase-matched, CEP-controlled keV soft-X-ray platform for attosecond spectroscopy of magnetic, quantum, and strongly correlated materials.
ER -