Backward lasing of singly ionized nitrogen ions pumped by femtosecond laser pulses

TL;DR

This paper demonstrates backward lasing at 391.4 nm in nitrogen ions pumped by femtosecond laser pulses, highlighting its potential for remote sensing applications.

Contribution

It reports the first observation of backward lasing in nitrogen ions pumped by 800 nm femtosecond pulses, with insights into optimal conditions and amplification mechanisms.

Findings

Backward lasing observed at 391.4 nm in nitrogen ions.

Optimal backward emission occurs at around 10 mbar pressure.

Backward lasing can be amplified using external seeding.

Abstract

We report on the observation of backward lasing at 391.4 nm of nitrogen ions pumped by linearly polarized intense femtosecond pulses at 800 nm. The strongly enhanced spectral intensity at 391.4 nm, as well as the amplification of an externally injected backward seeding pulse, confirm that the backward 391.4 nm signal is due to optical amplification in the gas plasma. Compared to the forward emission at 391.4 nm, the optimal backward emission is achieved at a lower gas pressure around 10 mbar, which is due to asymmetry of the backward and forward directions rooted in the traveling excitation geometry. This method, using the widely available 800 nm femtosecond pulses as a pump laser, provides a promising scheme for the generation of backward air laser, which holds a unique potential for optical remote sensing.