Generation of Raman lasers from nitrogen molecular ions driven by ultraintense laser fields

Jinping Yao,Zhaoxiang Liu,Ya Cheng,Wei Chu,Jinming Chen,Bo Xu

doi:10.1088/1367-2630/aab087

Abstract

Atmospheric lasing has aroused much interest in the past few years. The ‘air–laser’ opens promising potential for remote chemical sensing of trace gases with high sensitivity and specificity. At present, several approaches have been successfully implemented for generating highly coherent laser beams in atmospheric condition, including both amplified-spontaneous emission, and narrow-bandwidth stimulated emission in the forward direction in the presence of self-generated or externally injected seed pulses. Here, we report on generation of multiple-wavelength Raman lasers from nitrogen molecular ions (), driven by intense mid-infrared laser fields. Intuitively, the approach appears problematic for the small nonlinear susceptibility of ions, whereas the efficiency of Raman laser can be significantly promoted in near-resonant condition. More surprisingly, a Raman laser consisting of a supercontinuum spanning from ∼310 to ∼392 nm has been observed resulting from a series near-resonant nonlinear processes including four-wave mixing, stimulated Raman scattering and cross phase modulation. To date, extreme nonlinear optics in molecular ions remains largely unexplored, which provides an alternative means for air–laser-based remote sensing applications.

Highlights

The advent of ultrashort and ultraintense laser pulses has revolutionized the interaction of light with matter, giving rise to non-perturbative tunnel ionization which is the pillar stone of strong field laser physics [1]
Generation of coherent emissions in N+2 with mid-infrared pump lasers Figure 2(a) shows the dependence of fifth harmonic (FH) spectra on the gas pressure of nitrogen molecules obtained with pump pulses at a wavelength of 1580 nm
The gas pressure required for generating the supercontinuum decreases with the increase of the focal length of lens, implying that high laser intensity is necessary for generating the supercontinuum

Summary

Introduction

The advent of ultrashort and ultraintense laser pulses has revolutionized the interaction of light with matter, giving rise to non-perturbative tunnel ionization which is the pillar stone of strong field laser physics [1]. Lasing actions induced by tunnel ionization of nitrogen molecules have been observed which come as a major surprise to those who have been investigating strong field physics over the past three decades [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23] These observations were made with either a pump laser at 800 nm wavelength [6, 8,9,10,11,12,13,14,15,16,17,18,19,20,21] or that at longer wavelengths in the range between 1 and 4 μm [5, 7, 23]. The origin of the laser-like emissions observed only with the self-generated seed pulses (i.e., the harmonics of the pump laser) at pump wavelengths longer than 1 μm is another puzzle yet to be unlocked

Methods

Results

Discussion

Conclusion