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 f...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 semiinfinite gas cell,demonstrating the use of extended-medium geometries for effective production of IAPs.To gain a deeper understanding we develop a simulation method for high-order harmonic generation(HHG),which combines nonlinear propagation with macroscopic HHG solving the 3D time-dependent Schrödinger equation at the singleatom level.Our simulations reveal that the nonlinear spatio-temporal reshaping of the drivingfield,observed in the experiment as a bright plasma channel,acts as a self-regulating mechanism boosting the phase-matching conditions for the generation of IAPs.展开更多
We investigate the spatial characteristics of high-order harmonic radiation generated in argon and observe cross-like patterns in the far field.An analytical model describing harmonics from an astigmatic driving beam ...We investigate the spatial characteristics of high-order harmonic radiation generated in argon and observe cross-like patterns in the far field.An analytical model describing harmonics from an astigmatic driving beam reveals that these patterns result from the order and generation position-dependent divergence of harmonics.Even small amounts of driving field astigmatism may result in cross-like patterns,coming from the superposition of individual harmonics with spatial profiles elongated in different directions.By correcting the aberrations using a deformable mirror,we show that fine-tuning the driving wavefront is essential for optimal spatial quality of the harmonics.展开更多
基金funding from the European Union’s Horizon 2020 research and innovation programme(grant agreement No 871161,IMPULSE)and European Research Council(ERC):ERC Synergy grant agreement no.
文摘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 semiinfinite gas cell,demonstrating the use of extended-medium geometries for effective production of IAPs.To gain a deeper understanding we develop a simulation method for high-order harmonic generation(HHG),which combines nonlinear propagation with macroscopic HHG solving the 3D time-dependent Schrödinger equation at the singleatom level.Our simulations reveal that the nonlinear spatio-temporal reshaping of the drivingfield,observed in the experiment as a bright plasma channel,acts as a self-regulating mechanism boosting the phase-matching conditions for the generation of IAPs.
基金support from the Swedish Research Council(2013-8185,2021-04691,2017-04106,and 2021-05992)the European Research Council(advanced grant QPAP,884900)the Knut and Alice Wallenberg Foundation(KAW 2020.0111).
文摘We investigate the spatial characteristics of high-order harmonic radiation generated in argon and observe cross-like patterns in the far field.An analytical model describing harmonics from an astigmatic driving beam reveals that these patterns result from the order and generation position-dependent divergence of harmonics.Even small amounts of driving field astigmatism may result in cross-like patterns,coming from the superposition of individual harmonics with spatial profiles elongated in different directions.By correcting the aberrations using a deformable mirror,we show that fine-tuning the driving wavefront is essential for optimal spatial quality of the harmonics.
