Project without external funding

Plasma dynamics after femtosecond laser induced breakdown on water surface


Project Details
Project duration: 01/200412/2009


Abstract
The objective of this work is to study the dynamics of optical breakdown induced by ultrashort laser pulses at the surfaces of water. Laser-induced breakdown (LIB) in water has attracted much attention in the last decade due to its applications in precise ablation of biological tissues and microsurgery. The use of femtosecond laser pulses is especially interesting due to the high processing accuracy and low collateral damage in comparison with conventional lasers.
Even if it is generally accepted that the primary process in LIB is the generation of high density free electrons, the breakdown plasma dynamics in the early times of formation hasn"t been accurately resolved and plasma parameters like transient electron density and expansion velocity - important for an optimization of the breakdown event - haven"t been measured directly. By using a combination of transient imaging techniques together with spectrally resolved reflection spectroscopy we investigated the optical properties of the free electron plasma generated by 35fs laser pulses on the surface of a free flowing flat water jet. By analysing the data in the framework of a multireflection model, the transient electron density, electron-ion-recombination rate and plasma expansion velocity are accurately obtained.
The spectral emission of the breakdown plasma contains information about the laser-matter interaction process and the nature of the ablated medium. Previous studies have shown a dynamics of the breakdown plasma on the picosecond-time scale. By using an optical Kerr shutter one can observe the transient breakdown plasma emission spectra with a temporal resolution not yet achieved. Important parameters like the early stage plasma temperature and termalization time are also deduced.
The possibility of using adaptive pulse shaping techniques in order to increase the laser induced breakdown efficiency is also analysed.


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Last updated on 2017-11-07 at 15:01