Designs of hard x-ray attosecond delay lines for pump-probe and nonlinear spectroscopy

The advent of attosecond pulses, produced through high-harmonic generation, has transformed ultrafast science by enabling time-resolved studies with unparalleled temporal precision. Techniques like pump-probe spectroscopy, leveraging attosecond resolution, are crucial for probing and controlling electronic structure and dynamics at their natural timescales. Recently, free-electron laser facilities have successfully generated attosecond hard x-ray pulses by selectively lasing a single spike within a long electron bunch. This new mode of operation holds great potential for exploring electron motions with the desired, yet previously inaccessible spatial resolution offered by the atomic-scale wavelengths of x-rays. To bring attosecond pump-probe and time-resolved non-linear methodologies into the hard x-ray regime, this presentation will explore various hard x-ray delay line concepts using x-ray optics such as transmission gratings, mirrors, and prisms. Key aspects of these designs—including mechanisms for splitting and delay adjustment, system throughput, delay range, and achievable time resolution—will be discussed.