Time-resolved high harmonic spectroscopy of dynamical symmetry breaking in bi-circular laser fields

摘要: The bi-circular scheme for high harmonic generation, which combines two counter-rotating circular fields with frequency ratio 2:1, has recently permitted to generate harmonics essentially polarization, opening the way ultrafast chiral studies. This produces lines at 3N + 1 and 2 multiples of fundamental driving frequency, while are forbidden owing three-fold symmetry field. It is generally established that routinely observed signals these come from a slight ellipticity in fields, breaks symmetry. We find this neither only nor it dominant mechanism responsible. can be even perfectly circular, long pulses. show they encode rich information on sub-cycle electronic dynamics occur during generation process. By varying time delay relative intensity between drivers, we demonstrate when second either precedes or more intense than field, dynamical system broken by electrons trapped Rydberg orbits (i.e., Freeman resonances), witness this.