Jeremy Yeak

Plasma temperature clamping in filamentation laser induced breakdown spectroscopy.

Ultrafast laser filament induced breakdown spectroscopy is a very promising method for remote material detection. We present characteristics of plasmas generated in a metal target by laser filaments in air. Our measurements show that the temperature of the ablation plasma is clamped along the filament channel due to intensity clamping in a filament. Nevertheless, significant changes in radiation intensity are noticeable, and this is essentially due to variation in the number density of emitting atoms. The present results also explain the near absence of ion emission but strong atomic neutral emission from plumes produced during fs LIBS in air.

Dynamics of molecular emission features from nanosecond, femtosecond laser and filament ablation plasmas

The evolutionary paths of molecular and nanoparticle formation in laser ablation plumes are not well understood due to the complexity of numerous physical processes that occur simultaneously in a transient laser-produced plasma system. It is well known that the emission features of ions, atoms, molecules and nanoparticles in a laser ablation plume strongly depend on the laser irradiation conditions. We report the temporal emission features of AlO molecules in plasmas generated using a nanosecond laser, a femtosecond laser and filaments generated from a femtosecond laser. Our results show that, at a fixed laser energy, the persistence of AlO is found to be highest and lowest in ns and filament laser plasmas respectively while molecular species are formed at early times for both ultrashort pulse (fs and filament) generated plasmas. Analysis of the AlO emission band features show that the vibrational temperature of AlO decays rapidly in filament assisted laser ablation plumes.

Consequences of femtosecond laser filament generation conditions in standoff laser induced breakdown spectroscopy

The combination of femtosecond laser filament ablation and emission spectroscopy is a potential analytical tool for standoff characterization of samples of interest. We compare the emission features and physical conditions of plasmas generated from metal targets using either by loosely focused femtosecond filaments or by lens-free filaments. Our results show that the filament generation conditions influence the plasma properties appreciably which include the atomic and molecular emission features, persistence and plasma fundamentals (temperature and density). The loosely focused fs pulse filaments are found to generate ablation plumes with higher temperature and density along with increased persistence compared to plumes generated by lens-free filaments.

Dual-comb spectroscopy of laser-induced plasmas

We present the first results using broadband dual-comb spectroscopy in a laser-induced plasma. Preliminary results identifying 85Rb and 87Rb isotopes are shown using this technique.

Effect of Light Polarization on Plasma Distribution and Filament Formation

We show that filament formation has a strong dependence on the laser light polarization for 200 fs light at 790 nm. Filamentation does not exist for a pure circularly polarized light, propagating in vacuum before focusing in air, while there is no difference for focusing the light in air or vacuum for linearly polarized light.

Reconciling two views of IR filamentation in air: Bessel beams or plasma-confined beams?

Filaments prepared by letting a beam collapse, or by launching a ≪ 200µm beam from vacuum to atmosphere, are compared. The two types of filaments show different properties, characteristics of different theories about their nature.