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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Non-Linear Propagation of Ultrashort Mid-IR Pulses
摘要： Many atmospheric applications such as free-space communication or spectroscopy require targeted delivery of high-energy ultrashort pulses with a good beam quality. Often atmospheric turbulences complicate this task, causing random variations of the refractive index and resulting in fluctuations of light intensity on the target. Propagation of light in filamentation regime, when intensity is clamped, to a certain extent helps to overtake this problem, but brings ionization-related problems, such as energy loss, temporal pulse splitting, etc. Moreover, maximum peak power (cid:1842)(cid:3043)(cid:3032)(cid:3028)(cid:3038), which can be delivered in a single filament is limited to about ten critical powers of self-focusing (cid:1842)(cid:3030)(cid:3045)(cid:3036)(cid:3047), after which multiple filamentation and hence small-scale beam distortions take place. In the case of Ti:Sapphire drivers delivering 40-fs, 800-nm pulses, the energy in a single filament in air doesn’t exceed 1 mJ, unless special conditions are applied [1]. However, since (cid:1842)(cid:3030)(cid:3045)(cid:3036)(cid:3047)~(cid:2019)(cid:2870) ((cid:2019) is the driver wavelength), essentially more energy can be deposited in a single filament driven by 3.9-μm pulses [2]. Furthermore, mid-IR spectral range is beneficial in virtue of lower ionization rates and higher resistance to modulation instabilities and scattering by natural atmospheric obstacles, such as water droplets [3]. Finally, a unique combination of high atmospheric transparency and anomalous dispersion of air between 3.6-4.2 μm promote an opportunity for a lossless high-energy ultrashort pulse delivery and simultaneous solitonic self-compression [4]. However, multiple molecular resonances responsible for the anomalous dispersion also complicate filamentation dynamics by adding a new channel of energy loss, namely nonlinear enhanced absorption losses [2,5], when mainly stimulated rotational Raman scattering (SRRS) governs spectral dynamics dominated by an essential spectral redshift and immediate absorption of newly generated spectral components by CO2, having vibrational resonance in the vicinity of 4.2 μm. Due to this non-linearly enhanced absorption up to 50% of energy can be lost over several meters of propagation of 30 mJ 130-fs pulses [2]. However, since the intrapulse SRRS is sensitive to a temporal spacing between spectral components, pre-chirping of drivers pulses can help to reduce and control the energy loss. Moreover, we have demonstrated, that a proper choice of the chirp can also lead to ~5-fold self-compression in time and postponed onset of filamentation in space, what fulfils a goal of targeted high-energy ultrashort pulse delivery.
关键词： Ultrashort mid-IR pulses,filamentation,solitonic self-compression,nonlinear propagation,atmospheric applications
更新于2025-09-11 14:15:04
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Robust Remote Sensing of Trace-Level Heavy-Metal Contaminants in Water Using Laser Filaments
摘要： Water is the major natural resource that enables life on our planet. Rapid detection of water pollution that occurs due to both human activity and natural cataclysms is imperative for environmental protection. Analytical chemistry–based techniques are generally not suitable for rapid monitoring because they involve collection of water samples and analysis in a laboratory. Laser-based approaches such as laser-induced breakdown spectroscopy (LIBS) may offer a powerful alternative, yet conventional LIBS relies on the use of tightly focused laser beams, requiring a stable air–water interface in a controlled environment. Reported here is a proof-of-principle, quantitative, simultaneous measurement of several representative heavy-metal contaminants in water, at ppm-level concentrations, using ultraintense femtosecond laser pulses propagating in air in the filamentation regime. This approach is straightforwardly extendable to kilometer-scale standoff distances, under adverse atmospheric conditions and is insensitive to the movements of the water surface due to the topography and water waves.
关键词： filamentation,heavy-metal pollution,femtosecond laser pulse,remote sensing
更新于2025-09-11 14:15:04