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

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 ( + N 2 ), driven by intense mid-infrared laser fields. Intuitively, the approach appears problematic for the small nonlinear susceptibility of + N 2 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 nearresonant 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.

Recent Advances in Air Lasing: A Perspective from Quantum Coherence

“…As a simple illustration of recent observations of strong nonlinear optical effects in the N lasing experiments, Figure a shows that the 1580‐nm femtosecond laser enables the generation of bright spectral lines in N lasing, which can be significantly broadened to form a supercontinuum spectrum . The supercontinuum generation requires a proper gas pressure, a sufficiently high pump intensity, and a linearly polarized pump laser.…”

“…The solid angle of the radiation is about four orders of magnitude smaller than the 4π angle of the isotropic spontaneous emission . Lastly, such emission shows good temporal and spatial coherence, and follows an exponential growth along the plasma channel . The potential capability of generating strong, highly directional, and fully coherent emissions in the remote air provides exciting perspectives for the remote chemical sensing.…”

“…Similar to the atomic air lasing, resonant excitation is involved in the N lasing. The resonant interaction between the light and nitrogen molecular ions greatly enhances the nonlinear optical responses, which provides opportunities for studying ultrafast nonlinear optics with molecular ions …”

“…Calculated longest wavelengths of Stokes photons, corresponding to near‐resonant Raman scattering of R ( J ) photons from the initial , , , , rotational energy levels, are indicated with purple vertical dotted lines. (a) Adapted under the terms of the Creative Commons Attribution 3.0 licence . Copyright 2018, Institute of Physics.…”

Optimization of N2+ lasing through population depletion in the X2Σg+

“…This phenomenon, called "air lasing," has attracted researchers in the past two decades not only in the research field of remote sensing but also in the research field of atomic, molecular, and optical physics [1][2][3][4][5][6]. Among the air lasing, the lasing at 391 and 428 nm, corresponding, respectively, to the B 2 u + -X 2 g + (v , v ) = (0, 0) and (0,1) emission lines of N 2 + , has attracted special interest because the mechanism of the efficient preparation of N 2 + in the B 2 u + state, leading to the lasing action, has been mysterious [3,[7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”