Field-resolved measurements of soliton self-compressed single-cycle pulses and their application to water-window high-harmonic generation

Isolated attosecond pulses (IAPs) in the water window are critical for attosecond spectroscopy of chemical and biochemical dynamics. Their creation via high-harmonic generation (HHG) typically demands carrier-envelope phase (CEP) stabilization and complicated pulse compression of the ultrashort HHG driving pulses. This study describes field-resolved measurements of single-cycle pulses obtained through soliton self-compression of short-wave-infrared (1485 nm) femtosecond pulses. Pulse compression down to 1.1 optical cycles, corresponding to a duration of 5.05 fs, is demonstrated for 1.175 mJ pulses with 0.325 mJ within the full width at half-maximum of the pulse. High-harmonic generation in the water window is achieved with these pulses, and its dependence on the pulse compression is studied. It is also shown that IAPs are obtained for nearly any value of the CEP, which demonstrates that single-cycle pulses obtained from soliton self-compression enable the creation of IAPs without the requirement of a stable CEP. The results of this work open the path to attosecond time-resolved measurements in the water window, benefiting from the higher flux obtained with signal pulses (compared to idler pulses) of widely used optical parametric amplifiers.