Spectral Measurement and Calculation of Internal Pressure in Laser‐Induced Silicon Oxide Thin‐Film Plasma

ABSTRACT The pressure generated within a laser‐induced thin‐film plasma is a key factor driving plasma expansion and the formation of shock waves, which subsequently lead to mechanical damage to the thin film. Therefore, achieving quantitative diagnosis of this internal pressure is of great significance for understanding the mechanical mechanisms of laser‐induced damage. This paper proposes and develops a method to indirectly calculate the internal pressure of plasma based on Laser‐Induced Breakdown Spectroscopy (LIBS) technology. In the experiment, a nanosecond Nd: YAG pulsed laser (1064 nm) was focused on a silicon oxide thin‐film sample to generate plasma, and its emission spectrum was collected. The electron temperature of the plasma was calculated using the relative intensity ratio of spectral lines, and the electron density was determined through the Stark broadening effect. Under the premise of verifying that the plasma satisfies the condition of local thermal equilibrium (LTE), the internal pressure of the plasma under different laser energies was quantitatively solved by combining it with the ideal gas law. Research indicates that the electron temperature of the silicon oxide thin‐film plasma is on the order of 10 3 K and shows a decreasing trend with the increase in laser energy. The electron density is approximately 10 18 cm − 3 and does not change significantly with increasing laser energy. The calculated internal pressure of the plasma is on the order of 10 5 Pa and decreases slowly as the laser energy increases. This study successfully establishes a method for quantitatively obtaining the internal pressure of laser‐induced thin‐film plasma through spectral measurement, revealing the evolution pattern of internal pressure with laser energy under experimental conditions. The results provide key physical parameters for a deeper understanding of the mechanical effects in the interaction between lasers and thin‐film materials.