Temporally and spectrally resolved imaging of laser-induced plasmas

Expansion dynamics and chemistry evolution in ultrafast laser filament produced plasmas

Laser ablation in conjunction with optical emission spectroscopy is a potential non-contact, stand-off detection method for all elements in the periodic table and certain isotopes such as radionuclides. Currently, significant development efforts are on-going to use ultrafast laser filaments for remote detection of materials. The application of filaments is of particular interest in extending the range of stand-off capability associated with elemental and isotopic detection via laser-induced breakdown spectroscopy. In this study, we characterize the expansion dynamics and chemical evolution of filament-produced uranium (U) plasmas. Laser filaments are generated in the laboratory by loosely focusing 35 femtosecond (fs), 6 milli Joule (mJ) pulses in air. Time-resolved, two-dimensional plume and spectral imaging was performed to study hydrodynamics and evolution of U atomic and UO molecular emission in filament-produced U plasmas. Our results highlight that filament ablation of U plasmas gives a cylindrical plume morphology with an appearance of plume splitting into slow and fast moving components at later times of its evolution. Emission from the slow-moving component shows no distinct spectral features (i.e. broadband-like) and is contributed in part by nanoparticles generated during ultrafast laser ablation. Additionally, we find U atoms and U oxide molecules (i.e. UO, UxOy) co-exist in the filament produced plasma, which can be attributed to the generation of low-temperature plasma conditions during filament ablation.

Early-stage evolution of the plasma over KTiOPO4 samples generated by high-intensity laser radiations

The fundamental properties (electron temperature and density) at the early-stage evolution of plasma induced by laser-ablated KTiOPO(4) crystals are analyzed using an emission spectroscopy technique. The comparative studies give detailed insights into the influences of laser intensity and wavelength on the temporal evolution of the plasma. The lifetime of the plasma strongly depends on the laser intensity. The 532 nm laser beam can create hotter and denser plasma with faster expanding velocity than the 1064 nm laser beam.