engleski

Cavity ring-down spectorscopy of laser produced vapor and plasma

Cavity ring-down spectroscopy (CRDS) is a direct absorption technique, which has been in recent years applied in many environments from open air, static gas cells, supersonic expansions, flames to discharges and plasma jets. The basic principle of CRDS is quite simple: a short laser pulse is coupled into a stable cavity consisting of two highly reflecting curved mirrors. The quantity measured is the decay rate of photons in the cavity. It contains information about cavity losses and absorption and reflection of particles within the cavity. The short overview of this, by many considered as disruptive technology, will be given. We applied CRDS to detection of atoms and molecules present in the plume formed upon laser ablation of various metal (e.g. alkali) and non-metal targets (e.g. graphite). In these cases absorption of species changes significantly during the ring-down time. Therefore careful evaluation of ring-down decay constants in different time windows across the decay curves is needed. We show the potential of CRDS method to perform spatial and temporal analyses of the plume in respect to both ground and excited state neutral atoms and molecules. One can obtain data about particles velocities, rotational and vibrational temperatures and densities of particles in the plume. Several cases will be discussed: lithium and lithium containing targets and graphite where lithium dimers and carbon dimers (radicals) are observed. Versatility and applicability of the method will be discussed in respect to in-situ monitoring of vaporization processes relevant in pulsed laser deposition techniques or formation of nanostructures by laser ablation.

laser ablation; cavity ring-down spectroscopy

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