Enhanced resonant vibrational Raman scattering of N<sub>2</sub><sup>+</sup> induced by self-seeding ionic lasers created in polarization-modulated intense laser fields

J. Phys. B: At. Mol. Opt. Phys.

Lin

et al. 2021

We experimentally study the femtosecond supercontinuum (SC) generation using an optical vortex (OV) beam in water. It is demonstrated that the topological charge of the OV beam has little influence on spectral broadening induced by filament, while it has strong influence on spectral intensity. Despite the SC induced by filamentation of optical vortices in air possesses orbital angular momentums (OAMs), the SC generated in water and sapphire loses OAM. However, the light at central wavelength possesses OAMs after filamentation in transparent Kerr media. This study is helpful to the understanding of the physical mechanism of femtosecond SC generation by optical vortices in water.

Section: Resultsmentioning

confidence: 99%

Testing the coherence of supercontinuum generated by optical vortex beam in water

J. Phys. B: At. Mol. Opt. Phys.

Lin

et al. 2021

“…Particularly, some unique properties (e.g., the narrow spectrum, natural spatial overlap with the femtosecond driver laser, intrinsic delay with respect to the driver laser, and asymmetric temporal envelope) [20,21,[31][32][33] make it suitable as a probe to interrogate the Raman coherence. Hence, since air lasing was experimentally demonstrated, significant efforts have been paid to its applications in Raman spectroscopy [34][35][36][37][38][39]. With the nitrogen laser produced in N 2 -Ar gas mixture, Malevich et al performed a proof-of-principle experiment of gas sensing by measuring Raman gain or loss [35].…”

Section: Introductionmentioning

confidence: 99%

High-Sensitivity Gas Detection with Air-Lasing-Assisted Coherent Raman Spectroscopy

et al. 2022

Ultrafast Sci

Self Cite

Remote or standoff detection of greenhouse gases, air pollutants, and biological agents with innovative ultrafast laser technology attracts growing interests in recent years. Hybrid femtosecond/picosecond coherent Raman spectroscopy is considered as one of the most versatile techniques due to its great advantages in terms of detection sensitivity and chemical specificity. However, the simultaneous requirement for the femtosecond pump and the picosecond probe increases the complexity of optical system. Herein, we demonstrate that air lasing naturally created inside a filament can serve as an ideal light source to probe Raman coherence excited by the femtosecond pump, producing coherent Raman signal with molecular vibrational signatures. The combination of pulse self-compression effect and air lasing action during filamentation improves Raman excitation efficiency and greatly simplifies the experimental setup. The air-lasing-assisted Raman spectroscopy was applied to quantitatively detect greenhouse gases mixed in air, and it was found that the minimum detectable concentrations of CO2 and SF6 can reach 0.1% and 0.03%, respectively. The ingenious designs, especially the optimization of pump-seed delay and the choice of perpendicular polarization, ensure a high detection sensitivity and signal stability. Moreover, it is demonstrated that this method can be used for simultaneously measuring CO2 and SF6 gases and distinguishing 12CO2 and 13CO2. The developed scheme provides a new route for high-sensitivity standoff detection and combustion diagnosis.

“…Thus, since it was first reported, [13,14] various air-lasingbased Raman spectroscopic techniques have been explored. [19][20][21][22][23][24][25][26] In terms of practical applications, the most attractive one thereof is the single-beam background-free CRS technique developed recently. [24] Such the single-beam scheme has been proven to detect SF 6 gas in air with the concentration as low as 0.38%.…”

Section: Introductionmentioning

confidence: 99%

Electronic‐Resonance‐Enhanced Coherent Raman Spectroscopy with a Single Femtosecond Laser Beam

Xie

Laser & Photonics Reviews

et al. 2023

Self Cite

Coherent Raman scattering (CRS) spectroscopy holds versatile applications in many fields ranging from measuring temperature and concentration in reacting flows to imaging biological molecules in living cells. Although the powerful spectroscopic technique has been studied for a few decades, significant attention is still paid to developing state‐of‐the‐art CRS spectroscopy with the simpler design and higher sensitivity for practical applications in harsh or complex environments. Herein, a novel electronic‐resonance‐enhanced coherent Raman scattering (ERE‐CRS) technique is developed with a single femtosecond laser beam. Such single‐beam ERE‐CRS scheme is accomplished with the narrowband air lasing signal naturally generated in the interaction region as a probe source. The developed technique not only avoids fine spatio‐temporal control in the conventional multibeam configuration, but also accomplishes 1–2 orders of magnitude enhancement of 12CO2+${}^{12}{\mathrm{CO}}_{2}^{+}$ Raman signal due to the resonance of air lasing with electronic transition of the target gas. The dramatic enhancement effect is also manifested through the comparative measurements in CO2 isotopes. The single‐beam ERE‐CRS spectroscopy shows an unprecedented opportunity for the high‐sensitivity standoff detections of gas‐phase molecules and plasmas.