Multi-dimensional Simulation and Experimental Benchmarking of Ultrashort Pulsed Laser Interactions with Metallic Targets

Anastassiya Suslova, Purdue University

Abstract

In this work, ultrashort pulsed laser interactions with metallic targets and laser-induced effects were theoretically investigated, and the multi-dimensional simulation package FEMTO-2D was developed based on the solution of two non-linear heat conduction equations for electron and lattice sub-systems. Inverse Bremsstrahlung absorption was considered as primary light absorption mechanism. The laser-target interaction was assumed to occur at solid-like material density since laser pulse duration is orders of magnitude shorter than the time required for material thermal expansion. A theoretical approach based on the collision theory had been implemented to define the thermal dependence of target material optical properties and thermodynamic parameters (thermal conductivity and coupling factor) for electron and lattice sub-systems. Such approach allowed elimination of several fitted parameters commonly used in TTM based computer simulations. The developed simulation package has the capability to consider different angles of laser beam incidence and polarization effects which can be important for many applications. Also, the effect of the ballistic electron heat transport in metallic targets during laser-target interaction was directly accounted for based on the collision theory. Two material removal mechanisms (evaporation and explosive boiling) were developed and implemented to simulate the laser-induced ablation in 3D. With advancing of computer technology, integrated simulation packages became a popular tool of investigation of Ultrashort Pulsed Laser (USPL) interactions with various materials that help to enhance the physics and allows minimizing the extensive experimental costs for optimization of laser and target parameters for specific applications. In this work, our developed simulation package was utilized to predict the light absorption for several metallic targets as a function of wavelength and pulse duration on wide range of the laser intensity. For the first time to our knowledge, we investigated the role of the ballistic electrons in the initial heat redistribution processes during laser-target interaction in gold without relying on experimental data. We also have used our FEMTO-2D package to predict the damage threshold of gold-coated optical components with the focus on the role of the substrate materials as a heat sink for the gold film and the effect of the mirror layer thickness. Experimental work was also conducted at the Center for Materials Under eXtreme Environment (CMUXE) in the High Energy Density Physics laboratory (HEDP Lab) to benchmark the FEMTO-2D simulation predictions for USPL-induced ablation in copper using our femtosecond terra watt laser facility. Last, we investigated the properties of the laser ablation of metallic targets with ultrashort double pulses with a focus on the role of the pulse separation time when the latter does not exceed material thermal equilibration temperature.

Degree

Ph.D.

Advisors

Hassanein, Purdue University.

Subject Area

Nuclear engineering|Materials science

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