Ar 3pphotoelectron sideband spectra in two-color XUV + NIR laser fields

Abstract

We performed photoelectron spectroscopy using femtosecond XUV pulses from a free-electron laser and femtosecond near-infrared pulses from a synchronized laser, and succeeded in measuring Ar 3p photoelectron sideband spectra due to the two-color above-threshold ionization. In our calculations of the first-order time-dependent perturbation theoretical model based on the strong field approximation, the photoelectron sideband spectra and their angular distributions are well reproduced by considering the timing jitter between the XUV and the NIR pulses, showing that the timing jitter in our experiments was distributed over the width of + -1.0 0.4 0.2 ps. The present approach can be used as a method to evaluate the timing jitter inevitable in FEL experiments.

Time-resolved photoelectron angular distributions from nonadiabatically aligned CO2 molecules with SX-FEL at SACLA

“…Since the FEL pulses are generated by the self-amplified spontaneous emission (SASE) process [58], their intensities and temporal and spectral shapes vary significantly from shot to shot, and moreover the FEL pulses have a finite timing jitter on the order of ∼1 ps with the synchronized optical pulses [55]. Thus, in our experiment, the degrees of alignment were much decreased due to the inevitable timing jitter between the SX-FEL and NIR pulses, i.e., the fluctuation of t [55].…”

“…Since the FEL pulses are generated by the self-amplified spontaneous emission (SASE) process [58], their intensities and temporal and spectral shapes vary significantly from shot to shot, and moreover the FEL pulses have a finite timing jitter on the order of ∼1 ps with the synchronized optical pulses [55]. Thus, in our experiment, the degrees of alignment were much decreased due to the inevitable timing jitter between the SX-FEL and NIR pulses, i.e., the fluctuation of t [55]. To remove the degradation of the alignment due to the timing jitter, we tried to rearrange the single-shot ion images by referring to the theoretical values for the degree of alignment: Firstly, the degrees of alignment were calculated by solving the time-dependent Schrödinger equation according to [59].…”

“…The aligned molecular ensemble was prepared using the SACLA in-house Ti:sapphire NIR laser [54], and then evolves under field-free conditions. On one hand, the degree of alignment for the CO 2 molecular ensemble was determined by one of the facing velocity map imaging spectrometers (VMIs) [32,34,55], which recorded the momentum distribution of CO + fragment ions resulting from Coulomb explosion of the doubly-charged CO 2…”

Two-color XUV+NIR femtosecond photoionization of neon in the near-threshold region

“…Combining extreme ultraviolet (XUV) free-electron laser (FEL) radiation with intense optical or near infrared (NIR) laser fields opens up a wide range of laser assisted photoionization experiments [1][2][3][4][5][6][7]. Electrons emitted by XUV photoionization during an intense multi-cycle NIR field experience the quantum nature of the dressing field and can be shifted in energy by an integer number of NIR quanta, ±ÿω L , and hence change angular momentum.…”

“…To get more insight in the processes involved simulations were performed. Most reported sideband experiments so far have used photoelectron energies exceeding 15 eV that can be accurately described within the strong field approximation (SFA) approaches treating the emitted electron as a free particle interacting with the laser field without the influence of the parent ion [5,9,11]. For kinetic energies <15 eV more sophisticated approaches are necessary which take into account the simultaneous interaction of the electron with ionic and radiation fields.…”