Fragmentation dynamics of liquid–metal droplets under ultra-short laser pulses

Abstract

We present the measurements and theoretical analysis of the deformation and fragmentation of spherical liquid-metal drops by picosecond and subpicosecond laser pulses. In the experiments, 60 μm droplets of Sn-In alloy were irradiated by Ti:Sa laser pulses with a peak energy fluence of ∼100 J cm −2 . The observed evolution of the droplet shape dramatically differs from that previously reported for nanosecond pulses. Invoking 2D hydrodynamic simulations, we explain how, due to the specifics of matter dynamics in the liquid-vapor phase coexistence region, a liquid droplet is transformed into a characteristic acorn-like expanding shell with two inner cavities. High sensitivity of the measured shell parameters to the details of the equation of state and metastable dynamics suggests that such experiments offer new possibilities in exploration of thermophysical properties of metals in the region of liquidvapor phase transition.

kW-class picosecond thin-disc prepulse laser Perla for efficient EUV generation

“…The physical process related to laser irradiation of droplets has been recently studied in detail. 2,3 The basic architecture of the present LPP sources has been well-described in many research papers. [8][9][10] The latest achievement of a CE of 6% was reported, and a 375-W inburst EUV power at low duty cycle was demonstrated on test sources in the development laboratories.…”

“…The background physics of this phenomenon is under intensive physical and experimental study. 2,3 The typical repetition rate of the droplet generation is 100 kHz, and a further increase is necessary to kW generation due to the limit of the maximum input main laser pulse energy to keep the CE at 6% level. The requirements for the prepulse laser are relatively critical: a few mJ, good beam quality, a few ps, high pointing accuracy, and pulse-to pulse energy stability at 100-kHz repetition rate.…”

Modeling of liquid tin target deformation by laser pulse

“…Сходясь к центру мишени, амплитуда ударной волны сначала медленно затухает, а затем несколько увеличивается за счет гидродинамической фокусировки. В случае высокоинтенсивных пикосекундных лазерных импульсов, рассмотренных в [15], эффект фокусировки приводил к образованию обширной полости в центре мишени. Здесь этот эффект мал, так как амплитуда ударной волны на 3 порядка меньше, чем в [15], обширная полость не возникает, но появляется некоторая неоднородность плотности.…”

“…В случае высокоинтенсивных пикосекундных лазерных импульсов, рассмотренных в [15], эффект фокусировки приводил к образованию обширной полости в центре мишени. Здесь этот эффект мал, так как амплитуда ударной волны на 3 порядка меньше, чем в [15], обширная полость не возникает, но появляется некоторая неоднородность плотности. Важно заметить также, что после отражения от свободной границы возникают волны разрежения.…”

Generalized van der Waals equation of state for in-line use in hydrodynamic codes

“…Experiments with ultra-short laser pulses [1,2] have demonstrated that passage through the liquid-gas phase coexistence region may lead to very specific observational features that are difficult to predict and not easy to explain. Moreover, because of short time scales prevailing in laser experiments, one often confronts a dilemma of choosing between the metastable (MS) and the fully equilibrium (EQ) branches of EOS in the phase coexistence region that is not easy to resolve.…”