Numerical simulation of spatial and temporal evolution of laser-induced boron plasma using annular-point double pulse configuration

The annular–point double pulse laser-induced breakdown spectroscopy (DP-LIBS) is an effective way of significantly enhancing plasma parameters to amplify the spectral emission intensity for analysis of co-deposition layers in fusion devices. A two-dimensional numerical model, describing laser–material interaction, vapor plume expansion, plasma formation and laser–plasma interaction at a pressure of 10⁻⁴ mbar, was applied to investigate spatial and temporal evolutions of laser-induced boron plasma using annular–point double pulse configuration, which is crucial for analytical capabilities of LIBS techniques. The annular-point double pulse configuration demonstrated significant enhancement in plasma temperature compared to conventional single pulse configuration, under the same laser energy and laser fluence. At a laser fluence of 18 J/cm², we examined a series of inter-pulse delay times and found that the 20 ns delay time exhibited optimal performance, maintaining electron temperatures exceeding 2.5 eV for extended periods after the second pulse. Quantitatively, this optimal configuration achieved electron temperatures approximately 1.7–2.2 times as high as those in single-pulse configuration and maintained electron densities in the 10¹⁶–10¹⁷ cm⁻³ range. The temperature enhancement resulted from the collision between the annular pre-pulse plasma and the subsequent point pulse plasma, forming a well-defined stagnation layer.