Hystorical Background
Prior to 1990, we were actively involved in the field of low-threshold laser heating and plasma generation in front of solid targets. We performed irradiations in inert or chemically active ambient gases and demonstrated that plasma could be initiated in the presence of targets at intensities 1-2 orders of magnitude lower than in their absence. This effect, which is called laser optical breakdown, consists of a sequence of initial low-threshold vaporizations from surface defects and impurities followed by the landslide development of strongly ionised plasma in mixture with ambient gas. These fundamental and experimental achievements allowed us to stay in the lead of the then galloping research on how to induce the formation of surface compounds by high intensity pulsed laser irradiation (usually described as laser-induced direct chemical synthesis). Gas propelled into the melted layer covering the target surface was found to enhance the process through plasma and vapour recoil pressure.
MAIN RESEARCH
Pulsed Laser Deposition (PLD)
Pulsed laser deposition is a physical vapor deposition process, carried out in a vacuum system. In PLD, a pulsed laser is focused onto a target of the material to be deposited. For sufficiently high laser energy density, each laser pulse vaporizes or ablates a small amount of the material creating a plasma plume. The ablated material is ejected from the target in a highly forward-directed plume. The ablation plume provides the material flux for film growth. For multicomponent inorganics, PLD has proven remarkably effective at yielding epitaxial films
Matrix Assisted Pulsed Laser Evaporation (MAPLE)
MAPLE is a variation of conventional PLD. It provides, however, a less damaging approach for transferring many different organic and polymeric compounds that include small and large molecular weight species, from the condensed phase into the vapor phase. In MAPLE, a frozen
matrix consisting of a solution of a polymeric compound dissolved in a relatively volatile solvent is used as the laser target.
Combinatorial PLD / MAPLE
We introduced a combinatorial approach for the fabrication of inorganic and organic biopolymer thin films. Structures with compositional gradient are obtained by simultaneous laser ablation / vaporization of two distinct targets. C-PLD / MAPLE deposition methods were applied to obtain a compositional library of the two separate materials from the target to a single substrate.
Our main results during that period can be summarised as follows:
We were among the first to achieve the laser induced nitridation, carbidation or oxidation of metals and semiconductors in a surface layer of controlled thickness with gradient of concentration and properties.
We studied the initiation and development of surface periodical structures (ripples) with 2D and 3D architecture by multipulse laser irradiation of metals and semiconductors at an incident intensity around melting and/or vaporization threshold. We demonstrated the active role of the structures that could be used by a positive feed-back mechanism to significantly enhance the laser energy coupling and transfer to target. The generation of surface capillary and electromagnetic waves were proposed as the major mechanisms of laser radiation – plasma – target surface coupling in these processes.
We investigated the heterogeneous chemical reactions induced by cw or pulse laser radiation that led to a proved positive gain in isotope enrichment and substance separation.
After 1990, our earlier experience in laser-matter interactions and the concomitant improvement of our laser facilities enabled us to move on to applying laser plasmas to thin films depositions and/or modifications and further uses.