Isolated attosecond pulse generation in a semi-infinite gas cell driven by time-gated phase matching.

Isolated attosecond pulse (IAP) generation usually involves the use of short-medium gas cells operated at high pressures. In contrast, long-medium schemes at low pressures are commonly perceived as inherently unsuitable for IAP generation due to the nonlinear phenomena that challenge favourable phase-matching conditions. Here we provide clear experimental evidence on the generation of isolated extreme-ultraviolet attosecond pulses in a semi-infinite gas cell, demonstrating the use of extended-medium geometries for effective production of IAPs.

Robust Isolated Attosecond Pulse Generation with Self-Compressed Subcycle Drivers from Hollow Capillary Fibers.

High-order harmonic generation (HHG) arising from the nonperturbative interaction of intense light fields with matter constitutes a well-established tabletop source of coherent extreme-ultraviolet and soft X-ray radiation, which is typically emitted as attosecond pulse trains. However, ultrafast applications increasingly demand isolated attosecond pulses (IAPs), which offer great promise for advancing precision control of electron dynamics. Yet, the direct generation of IAPs typically requires the synthesis of near-single-cycle intense driving fields, which is technologically challenging.

Optimization of pulse self-compression in hollow capillary fibers using decreasing pressure gradients.

The improvement of techniques for the generation of near-infrared (NIR) few-cycle pulses is paving the way for new scenarios in time-resolved spectroscopy and the generation of ultrashort extreme-ultraviolet pulses through high-harmonic generation. In this work, we numerically study how to optimize the self-compression of NIR pulses using decreasing pressure gradients in hollow capillary fibers (HCFs). We identify a moderate nonlinear regime in which sub-cycle pulses are obtained with very good temporal quality from an input 30 fs pulse centered at a 800 nm wavelength and coupled as the fundamental mode of an argon-filled HCF fully evacuated at the output end.