Brilliant Source of 19.2-Attosecond Soft X-ray Pulses below the Atomic Unit of Time
Fernando Ardana‐Lamas, Seth L. Cousin, Juliette Ligneres, Jens Biegert
Abstract
Electronic correlations occur on attosecond timescales, dictating how chemical bonds form, energy flows, and materials respond to light. Capturing such many-body processes requires light pulses of similar duration. The soft x-ray water window is vital because it encompasses the principal absorption edges of carbon, nitrogen, and oxygen that underpin chemistry, biology, and materials science. However, generating and characterizing isolated attosecond pulses that reach into the soft x-ray water window has remained a challenge. We addressed this need and report an isolated attosecond soft x-ray pulse with a duration of 19.2 as. This pulse reaches into the water window and is shorter than the atomic unit of time of 24.2 as. The pulse is supported by a spectrum centered at 243 eV, extending up to 390 eV, and crossing the carbon K-edge with record photon flux: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mn>4.8</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>10</mml:mn> </mml:msup> </mml:math> photons per second overall and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mn>4.1</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>9</mml:mn> </mml:msup> </mml:math> photons per second in a 10% bandwidth at the carbon K-shell edge (284 eV). Such an extremely short, soft x-ray pulse combines extreme temporal resolution with a coherent, ultrabroadband soft x-ray spectrum, opening new opportunities to study electron dynamics in atoms, molecules, and solids, to disentangle many-body interactions in correlated systems, and to follow nonadiabatic energy flow in molecular complexes. Our results establish a new benchmark for table-top attosecond technology and lay the foundation for its widespread application in science and technology.