研究目的
Investigating the role of rotational excitation in the coherent and unidirectional B 2Σ+u emission of N2+ at 391 nm, known as air lasing, when N2 is irradiated with intense femtosecond near-infrared laser pulses at 800 nm.
研究成果
The study reveals that population inversion can be achieved in N2+ between rotationally highly excited levels in the B 2Σ+u state and those in the X 2Σ+g state, leading to lasing at 391 nm, even when the total population in the B(v' = 0) state is not inverted with respect to the total population in the X(v'' = 0) state. This finding is significant for understanding the mechanism of air lasing and could inform future experimental and theoretical studies.
研究不足
The study is limited by the assumptions made in the simulation, such as the sudden generation of N2+ in an intense ultrashort laser pulse and the focus on specific vibrational and rotational states. The effect of rotational pre-excitation of neutral N2 before ionization is found to be minimal but not negligible.
1：Experimental Design and Method Selection:
The study involves simulating the time-dependent population transfer process of N2+ by including vibrational and rotational degrees of freedom. The methodology is based on solving the time-dependent Schr?dinger equation for the N2+ system interacting with a laser field.
2：Sample Selection and Data Sources:
The study assumes N2+ is generated suddenly in an intense ultrashort laser pulse and focuses on the vibrational and rotational states of N2+.
3：2+.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: The primary equipment includes intense femtosecond near-infrared laser pulses at 800 nm.
4：Experimental Procedures and Operational Workflow:
The simulation involves solving the time-dependent Schr?dinger equation with a sufficiently small time step, assuming N2+ is prepared in the X 2Σ+g (v = 0) state at t =
5：Data Analysis Methods:
The time-dependent variation of the populations in the rotational levels is evaluated as the thermal average of the populations in the rotational levels.
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