title: Dense ionization and subsequent non-homogeneous radical-mediated chemistry of femtosecond laser-induced low density plasma in aqueous solutions: synthesis of colloidal gold.
abstract: The "cold" low density plasma channels generated by the filamentation of powerful femtosecond laser pulses in aqueous solutions constitute a source of dense ionization. Here, we probed the radiation-assisted chemistry of water triggered by laser ionization via the radical-mediated synthesis of nanoparticles in gold chloride aqueous solutions. We showed that the formation of colloidal gold originates from the reduction of trivalent ionic gold initially present in solution by the reactive radicals (e.g. hydrated electrons) produced upon the photolysis of water. We analyzed both the reaction kinetics of the laser-induced hydrated electrons and the growth kinetics of the gold nanoparticles. Introduction of radical scavengers into the solutions and different initial concentrations of gold chloride provided information about the radical-mediated chemistry. The dense ionization results in the second order cross-recombination of the photolysis primary byproducts. Competition with recombination imposes the non-homogeneous interaction of reactive radicals with solute present in irradiated aqueous solutions. Such a laser-induced non-homogeneous chemistry suggests similarities with the radiation chemistry of water exposed to conventional densely ionizing radiation (high dose rate, high linear energy transfer).
authors.affiliation: Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada. hakim.belmouaddine@usherbrooke.ca Daniel.Houde@Usherbrooke.ca.
authors.forename: Hakim
authors.identifier: http://orcid.org/0000-0003-2797-7316
authors.initials: H
authors.lastname: Belmouaddine
authors.affiliation: Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada. hakim.belmouaddine@usherbrooke.ca Daniel.Houde@Usherbrooke.ca.
authors.forename: Minghan
authors.initials: M
authors.lastname: Shi
authors.affiliation: Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada. hakim.belmouaddine@usherbrooke.ca Daniel.Houde@Usherbrooke.ca.
authors.forename: Paul-Ludovic
authors.initials: PL
authors.lastname: Karsenti
authors.affiliation: Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada. hakim.belmouaddine@usherbrooke.ca Daniel.Houde@Usherbrooke.ca.
authors.forename: Ridthee
authors.initials: R
authors.lastname: Meesat
authors.affiliation: Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada. hakim.belmouaddine@usherbrooke.ca Daniel.Houde@Usherbrooke.ca.
authors.forename: Léon
authors.initials: L
authors.lastname: Sanche
authors.affiliation: Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada. hakim.belmouaddine@usherbrooke.ca Daniel.Houde@Usherbrooke.ca.
authors.forename: Daniel
authors.initials: D
authors.lastname: Houde