Sub-cycle coherent control of ionic dynamics via transient ionization injection

Abstract

We investigate the interwoven dynamic evolutions of neutral nitrogen molecules together with nitrogen ions created through transient tunnel ionization in an intense laser field. By treating the molecules as open quantum systems, it is found that considering real-time injection of ions and strong couplings among their electronic states, nitrogen molecular ions are primarily populated in the electronically excited states, rather than staying in the ground state as predicted by the well-known tunneling theory. The unexpected result is attributed to sub-cycle switch-on of timedependent polarization by transient ionization and dynamic Stark shift mediated near-resonant multiphoton transitions. Their combined contribution also causes that the vibrational distribution of N + 2 does not comply with Franck-Condon principle. These findings corroborate the mechanism of nitrogen molecular ion lasing and are likely to be universal. The present work opens a new route to explore the important role of transient ionization injection in strong-field induced non-equilibrium dynamics.The fundamental process of strong field ionization of atoms by intense ultrashort laser pulses occurs at attosecond timescale [1-3] and lasts for pulse lengths in femtoseconds. The temporal confined strong field ionization (SFI) creates broad bandwidth non-stationary ionic states along with launching of attosecond electron wavepacket forming the foundation of attoseond physics [4][5][6][7][8]. One of the key problem is how the coherence of the ionic states affect the subsequent ultrafast nonequilibrium evolution ranging from charge migration in molecules [9], electron transport in condense matter [10] to ultrafast laser processing of materials [11]. It is particular intriguing to question wether the further interaction of the ions with lasers can be considered independently by assuming the prior ionization is completed?Recent experiments indicate that the interplay of subcycle SFI and the followed ion-laser coupling is indispensable for nitrogen molecular ion lasing [12][13][14][15][16] which suggests the new possibility to manipulate the ion coherence upon its creation toward ion-based quantum optics. While SFI itself can be described well by the celebrated Keldysh tunneling theory [17], a complete model treating both ionization of neutrals and laser-ion couplings on the equal footing is still lacking. Theoretically, dealing with bounded multi-electron problem is already a difficult task, it is even challenging for open quantum many-body systems when ionization is involved. Exact time-dependent multilelectron theories are limited to two electrons cases [18] or struggling with ionization-induced derivative discontinuities in density-functionals [19]. A lot of theoretical works have devoted to the coherent ionic evolution in a multi-channel formalism [20,21] but the ion-laser coupling within the ionization process remains elusive.The current work attempts to address the fundamental question of how the transient SFI will influence the quantum states of th...

Rotational quantum beat lasing without inversion

“…Regarding optical X → B excitation by an 800 nm pump, the |X, ν = 0 → |B, ν = 0 transition corresponds to absorption of two photons, which is parity forbidden; noticeable excitation is only generated at very high intensities, I 4 × 10 14 W/cm 2 (the domain of several recent pump-probe experiments but not relevant for standard laser filamentation conditions), when the system is strongly distorted and higher-order multiphoton transitions can occur. In this context, note that strong-field ionization populates not field-free 25,41,42,45,50 but already polarized (dressed by the field) ionic X, A, and B states. Indeed optical tunneling results from polarization of the many-body wave function of the neutral as one of the polarized electrons leaks through the potential barrier, leaving other electrons polarized.…”

Control of N2+ air lasing

“…Focusing a powerful near-infrared femtosecond laser into air reveals gain on transitions in the ultraviolet between the different vibrational states of the upper B 2 + u and the ground X 2 + g electronic states of the nitrogen molecular cation [1]. Pump laser pulses near 800 nm move population from the ground state to the middle A 2 u state of the ion [2][3][4][5][6][7][8][9][10][11][12], which initiates a vibrational wave packet that can temporarily trap population [2,3,5]. The X 2 + g to A 2 u interaction contributes to gain by depleting the ground state, but it also enables control of the gain and emission.…”

Rotational Quantum Beat Lasing without Inversion

“…Regarding optical X → B excitation by an 800 nm pump, the |X , ν = 0 → |B, ν = 0 transition corresponds to absorption of two photons, which is parity forbidden; noticeable excitation is only generated at very high intensities I 4 × 10 14 W/cm 2 (the domain of several recent pump-probe experiments but not relevant for standard laser filamentation conditions) when the system is strongly distorted and higher-order multiphoton transitions can occur. In this context, note that strong-field ionization populates not field-free [25,41,42,45,53] but already polarized (dressed by the field) ionic X , A, and B states. Indeed, optical tunneling results from polarization of the many-body wave function of the neutral as one of the polarized electrons leaks through the potential barrier, leaving other electrons polarized.…”