Abstract
Evolution of plasma plume generation on the surface of metal irradiated by laser beam with the mean radiation flux density ~ 106 W/cm2 in the external electric field with different polarity and field strength from 0 to 106 V/m was experimentally investigated. It is shown that the mean size of metal droplets carried out from the irradiated zone of target becomes materially (in several times) smaller when of the external electric field strength amplitude grow, independently to its polarity. It is essential that the mentioned differences (at the considered parameters of laser radiation) are observed only at the initial stage of the laser plume development, because after the steam-plasma cloud reaches the electrode an electric breakdown (short-circuit) occurs, and the external field in the interelectrode gap disappears. Electric breakdown leads to the spasmodic increase of electron density and temperature of plasma and to effective absorption of laser radiation by plasma torch (shielding of the target). In consequence of shielding droplets generation happens only during electric field existence. This explains decrease by several times of the characteristic size of the target substance droplets in spite of short duration of electric field existence.
Highlights
In the publication [1] was shown that under the action of laser radiation with the mean radiation flux density ∼ 106 W/cm2 at the surface of some metals (Cu, Al, Sn, Pb, In) in the external electric field with different polarity and the strength up to 106 V/m the mean size of the target substance droplets carried out of the irradiated zone decreases by several times with increasing external electric field strength in spite of short duration of electric field existence
The studies performed have shown that evolution of plasma plume generation on the surface of metal (Cu, Al, Sn, Pb, In) irradiated by laser beam with the mean radiation flux density ∼106 W/cm in the external electric field with different polarity and field strength from 0 to 106 V/m was experimentally investigated
It is shown that the mean size of metal droplets carried out from the irradiated zone of target becomes materially smaller when of the external electric field strength amplitude grow, independently to its polarity
Summary
In the publication [1] was shown that under the action of laser radiation with the mean radiation flux density ∼ 106 W/cm at the surface of some metals (Cu, Al, Sn, Pb, In) in the external electric field with different polarity and the strength up to 106 V/m the mean size of the target substance droplets carried out of the irradiated zone decreases by several times with increasing external electric field strength in spite of short duration of electric field existence. The aim of the present work is to study the influence of electric fields of different strength (from 0 to 106 V/m) on the spatial and temporal evolution of the laser plasma arising under the action of millisecond laser pulses at the surface of metals and to explain the mentioned effect. A part (4 %) of laser radiation from the front face of the glass wedge (5) was directed into the IMO-2N energy meter (6). Energy of the laser pulse varied from 10 to 60 J. To record the temporal shape of the laser pulse we used coaxial photo-detector FEK-14 (8). High-speed holographic cinematography method [2] was used to study the temporal and spatial evolution of the plasma plume near the sample treated by laser radiation
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