Two-photon resonant excitation of a doubly excited state in He atoms by high-harmonic pulses

Abstract

We experimentally demonstrate a two-color two-photon resonant excitation of the doubly excited 2p 2 1 S state in helium atoms by the combination of 19th and 21st harmonic photons of a Ti:sapphire laser. Production of the 2p 2 1 S state is confirmed by the experimental observation that the electron emission from this state does not depend on the direction of harmonic polarization. Our ab-initio theoretical results through the solution of time-dependent Schrödinger equation are consistent with the experimental results and confirm the first successful production of a doubly excited state by high-harmonic pulses.

Quantum coherent control of the photoelectron angular distribution in bichromatic-field ionization of atomic neon

“…Phase control for two-color setups, such as with ω and 2 ω, towards final states with equal parities (e.g., ω + ω + ω + ω and 2 ω + 2 ω) can already be seen in the angle-integrated probability of the electron or ion yields [20,21]. In contrast, mixing states of different parities can only be observed in differential characteristics, such as the photoelectron angular distribution (PAD).…”

Design Study of Time-Preserving Grating Monochromators for Ultrashort Pulses in the Extreme-Ultraviolet and Soft X-Rays

“…Since multiple orders of high harmonics are generated coaxially with the fundamental laser pulses, the application to time-resolved spectroscopy often requires a suitable monochromatizing system to select a single harmonic and reject the adjacent orders and the laser radiation. Furthermore, monochromatization may be important for imaging applications where high spectral purity is required [12,13]. Some of the existing FEL beamlines have grating monochromators either to increase the spectral purity of the source or to select the harmonics of the FEL emission and filter out the fundamental [14][15][16].…”

Grating Configurations for the Spectral Selection of Coherent Ultrashort Pulses in the Extreme-Ultraviolet

“…As many multiple orders of high harmonics are generated coaxially along with the intense fundamental laser pulses, the application to time-resolved and nonlinear spectroscopy may give some difficulties since the target signals probed by an appropriate harmonic order are often covered with the noises caused by the other harmonic orders [9], therefore, a suitable monochromatizing system may be required to select a single harmonics. Furthermore, monochromatization may be important for imaging applications as a high spectral purity is necessary to achieve a high resolution in imaging [10].…”