**Experimental Determination of Electronic Density and Temperature in Water-Confined Plasmas Generated by Laser Shock Processing**

### **Cristóbal Colón 1,\*, María Isabel de Andrés-García 1, Cristina Moreno-Díaz 1, Aurelia Alonso-Medina 1, Juan Antonio Porro 2, Ignacio Angulo 2 and José Luis Ocaña 2**


Received: 17 June 2019; Accepted: 19 July 2019; Published: 22 July 2019

**Abstract:** In this work, diagnoses of laser-induced plasmas were performed in several Laser Shock Processing (LSP) experiments using the Balmer H α-line (656.27 nm) and several Mg II spectral lines. A Q-switched laser of Nd:YAG was focused on aluminum samples (Al2024-T351) in LSP experiments. Two methods were used to diagnose the plasma. The first method, which required two di fferent experiments, was the standard for establishing the electronic temperature through the use of a Boltzmann Plot with spectral lines of Mg II and self-absorption correction. The Stark width of the Balmer H α-line was used to determine the electron density in each of the cases studied. The second method had lower accuracy, but only required an experimental determination. Two parameters, the electronic temperature and the electron density, were obtained with the aid of the H α-line in a single data acquisition process. The order of magnitude of the temperature obtained from this last method was su fficiently close to the value obtained by the standard method (within a factor lower than 2.0), which is considered to be important in order to allow for its possible use in industrial conditions.

**Keywords:** laser shock processing; plasma diagnosis; electron density
