CC BY
10LM-O-19
LASER-MATTER INTERACTION
Pressure pulse in nanosecond laser ablation of mercury due to metal-nonmetal transition: analysis of resent experimental results.
A.A. Samokhin, P.A. Pivovarov
Prokhorov General Physics Institute of the Russian Academy of Sciences, 119991, Moscow, Vavilov str., 38, Russia
e-mail: [email protected]
In a recent experiment on laser ablation of mercury [1], two features were found in the behavior of the pressure generated in the target: the formation of an additional peak on the pressure pulse and a reduction in the observed delay time At for the arrival of the pressure signal from the irradiated region to the piezoelectric sensor. This report presents theoretical estimates confirming the occurrence of these features due to the metal-nonmetal transition (MNT).
With the help of data on the shock compression of mercury [2, 3], the change in the signal delay At recorded in [1] was used to determine the shock wave pressure required for this variation. For the cases of At = 15 and 50 ns, these pressures are equal to 2630 and 9100 bar, which are approximately 8 times higher than the pressure values indicated in [1] obtained by calibrating the sensor with a conventional thermoacoustic signal in the region of normal boiling temperature. This difference is associated with a change in the calibration coefficient for evaporation pressure signals, the effective area of which is smaller than the thermoacoustic one. An independent estimation of the calibration change can be obtained from the ratio of evaporation pressure (P2 = 0.56 Ps =560 bar) corresponding to the expected onset of clarification (p = 9, T = 1560 K) [4] to the signal value indicated in [1] at a level of ~ 65 bar. This gives about the same correction factor ~8.
Within the framework of the two-wave approach [5], the following estimations were obtained for the speed of the bleaching MNT front d = 165 and 340 m/s, additional pressure ahead of the front P1 = 2610 and 9100 bar and the required intensity absorbed at the front Id = 2.9-107 and 5.9-107 W/cm2 for this cases. Estimation of the required total absorbed intensity, taking into account the evaporation process and low absorption in the nonmetal layer for these two cases, gives to the surface absorption coefficient A ~ 0.62 and 0.76.
These results are consistent with the assumption about the experimental observation in [1] of the MNT effect during laser ablation of mercury. Further experimental and theoretical studies are needed to elucidate all the main features of the nonequilibrium behavior of metals in the region of their critical parameters, which continue to be insufficiently studied even for mercury.
[1] Samokhin, A.A., Pivovarov, P.A., Shashkov, E.V. et al. On the Metal-Nonmetal Transition under Nanosecond Laser Ablation. Phys. Wave Phen. 29, 204 (2021)
[2] LASL shock Hugoniot data / Stanley P. Marsh, editor. Berkeley; London : University of California Press (1980), 658
[3] A.I. Funtikov, Shock adiabat, phase diagram, and viscosity of mercury at a pressure up to 50 GPa, High Temperature, 47(2) 201 (2009)
[4] I.K. Kikoin, A.P. Senchenkov, S.P. Naurzakov, E.B. Gelman, Perehod metall-nemetall v plotnom metallicheskom pare, Thesis IAE-2310, Moscow 1973 (in Russian)
[5] A.A. Samokhin, P.A. Pivovarov On the mathematical model of combined rarefaction and compression waves in condensed matter Mathematica Montisnigri , 50, 104 (2021).
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