Alignment-Dependent Fluorescence Emission Induced by Tunnel Ionization of Carbon Dioxide from Lower-Lying Orbitals

Abstract

Study on ionization process of molecules in an intense infrared laser field is of paramount interest in strong-field physics and constitutes the foundation of imaging of molecular valence orbitals and attosecond science. We show measurement of alignment-dependent ionization probabilities of the lower-lying orbitals of the molecules by experimentally detecting alignment-dependence of fluorescence emission from tunnel ionized carbon dioxide molecules. The experimental measurements are compared with the theoretical calculations of strong field approximation (SFA) and molecular ADK models. Our results demonstrate the feasibility of an all-optical approach for probing the ionization dynamics of lower-lying orbitals of molecules, which is still difficult to achieve until now by other techniques. Moreover, the deviation between the experimental and theoretical results indicates the incompleteness of current theoretical models for describing strong field ionization of molecules.

Coupling ofN2+rotational states in an air laser from tunnel-ionized nitrogen molecules

“…When the pump 800-nm pulse interacts with the molecule, the initial state |J i ,M i will evolve into the superposition of a series of coherent states|J ,M i , which can be expressed with a general form as follows: where A J and φ J are the amplitude and the phase of the transition from |J i ,M i to |J ,M i , E J is the eigenenergy of the state |J ,M i , and t denotes the time after the interaction of the molecules with the 800-nm pump pulse. Later on, upon the arrival of the probe pulse, the state |J ,M i will experience a transition to the final state |J,M i after interacting with the 400-nm probe pulse, and the modulated rotational wave packet can be expressed as [20][21][22] …”

Weak-field asymptotic theory of tunneling ionization including the first-order correction terms: Application to molecules

“…Indeed, the ionization yields are often directly compared with the shape of molecular orbitals in both experimental [41,42] and theoretical [33,43] papers. However, many of the recent studies [44][45][46][47][48] community [49]. In this section, we address this issue in the example of H 2 + .…”

Amplified Emissions Spectroscopy for Sensing Applications

“…[2,3] Due to a variety of nonlinear effects on atoms or molecules induced by such strong fields in a filament, femtosecond laser filamentation not only is involved in rich physical phenomena such as high harmonic generation, [4] terahertz radiation, [5] and alignment-dependent fluorescence emission but also triggers a series of promising applications including lightning control and remote sensing. [6][7][8] In particular, the laser intensity inside a filament is high enough to induce population inversion, giving rise to amplified emission spectroscopy from the ionized molecules or fragments. In addition, during the last 5 years, the development of high-gain backward amplified emission induced by resonance enhanced multiphoton ionization has spearheaded the surge of research on air lasing.…”