Gain dynamics of a free-space nitrogen laser pumped by circularly polarized femtosecond laser pulses

TL;DR

This study investigates the ultrafast gain dynamics of a nitrogen laser at 337 nm pumped by circularly polarized femtosecond pulses, revealing population inversion timescales, decay behavior, and oxygen quenching effects.

Contribution

It provides the first detailed experimental analysis of nitrogen laser gain dynamics under circularly polarized femtosecond laser pumping, including pressure and oxygen effects.

Findings

Population inversion occurs within several picoseconds.

Decay of the laser signal depends on nitrogen pressure.

Oxygen molecules significantly quench the nitrogen laser.

Abstract

We experimentally demonstrate ultrafast dynamic of generation of a strong 337-nm nitrogen laser by injecting an external seed pulse into a femtosecond laser filament pumped by a circularly polarized laser pulse. In the pump-probe scheme, it is revealed that the population inversion between the excited and ground states of N2 for the free-space 337-nm laser is firstly built up on the timescale of several picoseconds, followed by a relatively slow decay on the timescale of tens of picoseconds, depending on the nitrogen gas pressure. By measuring the intensities of 337-nm signal from nitrogen gas mixed with different concentrations of oxygen gas, it is also found that oxygen molecules have a significant quenching effect on the nitrogen laser signal. Our experimental observations agree with the picture of electron-impact excitation.