Remote Detection of Uranium Using Self-Focusing Intense Femtosecond Laser Pulses

Sensing with Femtosecond Laser Filamentation

Femtosecond laser filamentation is a unique nonlinear optical phenomenon when high-power ultrafast laser propagation in all transparent optical media. During filamentation in the atmosphere, the ultrastrong field of 10¹³-10¹⁴ W/cm² with a large distance ranging from meter to kilometers can effectively ionize, break, and excite the molecules and fragments, resulting in characteristic fingerprint emissions, which provide a great opportunity for investigating strong-field molecules interaction in complicated environments, especially remote sensing. Additionally, the ultrastrong intensity inside the filament can damage almost all the detectors and ignite various intricate higher order nonlinear optical effects. These extreme physical conditions and complicated phenomena make the sensing and controlling of filamentation challenging. This paper mainly focuses on recent research advances in sensing with femtosecond laser filamentation, including fundamental physics, sensing and manipulating methods, typical filament-based sensing techniques and application scenarios, opportunities, and challenges toward the filament-based remote sensing under different complicated conditions.

Iterative wavefront optimization of ultrafast laser beams carrying orbital angular momentum

Structured intense laser beams offer degrees of freedom that are highly attractive for high-field science applications. However, the performance of high-power laser beams in these applications is often hindered by deviations from the desired spatiotemporal profile. This study reports the wavefront optimization of ultrafast Laguerre-Gaussian beams through the synergy of adaptive optics and genetic algorithm-guided feedback. The results indicate that the intensity fluctuations along the perimeter of the target ring-shaped profile can be reduced up to ∼15%. Furthermore, the radius of the ring beam profile can be tailored to a certain extent by establishing threshold fitting criteria. The versatility of this approach is experimentally demonstrated in conjunction with different focusing geometries.

Laser beam steering automation with an Arduino-based CNC shield for standoff femtosecond filament-induced breakdown spectroscopic studies

In this study, we report a novel, to the best of our knowledge, instrumentation procedure in the automation of laser beam steering for raster/spiral scanning of the samples used in standoff femtosecond laser-induced breakdown spectroscopy (LIBS) experiments. We have used a readily available and easy-to-handle Arduino-based computerized numerical control (CNC) shield along with the free software, universal G-code sender, for the automation. Standoff femtosecond filamentation-induced breakdown spectra (St-Fs-FIBS) of metals, three compositions of Ag-Au alloy, and polyvinyl chloride, unplasticized polyvinyl chloride, and chlorinated polyvinyl chloride plastic samples were recorded using the developed automated experimental setup. The St-Fs-FIBS spectra were recorded at a standoff distance of ∼5m utilizing a simple hand-held spectrometer. Furthermore, principal component analysis technique was utilized for the successful classification of three compositions of Au-Ag alloy spectra using their St-Fs-FIBS spectral data.

Filament-induced breakdown spectroscopy with structured beams

Filament-induced ablation represents an attractive scheme for long-range material identification via optical spectroscopy. However, the delivery of laser energy to the target can be severely hindered by the stochastic nature of multiple-filamentation, ionization of ambient gas, and atmospheric turbulence. In order to mitigate some of these adverse effects, we examine the utility of beam shaping for femtosecond filament-induced breakdown spectroscopy with Gaussian and structured (Laguerre-Gaussian, Airy, and Bessel-Gaussian) beams in the nonlinear regime. Interaction of filaments with copper, zinc, and brass targets was studied by recording axially-resolved broadband emission from the filament-induced plasma. The laser-solid coupling efficacy was assessed by inferring thermodynamic parameters such as excitation temperature and electron density. While under our experimental conditions the ablation rate with Gaussian- and Laguerre-Gaussian beams is found to be similar, the Airy and Bessel-Gaussian beams offer the advantage of longitudinally extended working zones. These results provide insights into potential benefits of structuring ultrafast laser beams for standoff sensing applications.