In the pursuit of enhancing the output capabilities of high-power solid laser devices for applications, such as inertial confinement fusion (ICF) and high-energy particle physics, the laser-induced damage threshold (LIDT) of optical components remains a critical limitation. Traditional mechanical polishing techniques yield surfaces with LIDT values significantly lower than their intrinsic breakdown thresholds. This study aims to address these limitations by developing a novel method using laser-induced breakdown atmospheric plasma to effectively remove surface defect layers in fused quartz components, thereby improving their resistance to laser damage.

In the experimental setup, an Nd∶YAG laser system, capable of generating both fundamental (1ω, the wavelength of 1064 nm) and third harmonic (3ω, the wavelength of 355 nm) laser beams, is employed. The system includes energy regulators, high-precision translation stages, and high-resolution cameras for monitoring. Fused quartz samples (the size of 10 mm×10 mm×2 mm) are subjected to ultrasonic cleaning and dried before experimentation. The laser-induced breakdown plasma is created by focusing the 1ω laser beam into ambient air, allowing for the controlled removal of defect layers by adjusting the sample movement speed while maintaining consistent laser pulse energy (120 mJ) and distance from the plasma to the sample (approximately 90 μm). The root-mean-square (RMS) roughness and ultraviolet laser damage performance are evaluated before and after the removal process using the profilometry, scanning electron microscope (SEM), and atomic force microscope (AFM).

Results demonstrate that the removal depth and surface roughness exhibit a nonlinear relationship with varying sample movement speeds. As the movement speed increases, the average removal depth initially decreases before stabilizing, while the RMS roughness shows a corresponding reduction followed by an increase (Table 1). The optimal movement speed is identified as 5 μm?s-1, at which the roughness is minimized. The LIDT measurements reveal a significant improvement: when the removal depth reaches 0.3 μm, the LIDT increases to 29.8 J/cm2, and a 1.9-fold enhancement is realized when compared to that of the untreated surface. This increase is attributed to the effective elimination of contaminants and subsurface micro-cracks, which is confirmed via SEM imaging (Fig. 5). Further analysis indicates that although increasing removal depths initially improves LIDT, excessive removal leads to the exposure of subsurface defects that degrade surface quality and reduce LIDT.

The study successfully validates a new method for the removal of surface defect layers in fused quartz using laser-induced breakdown plasma. This technique presents significant advantages over traditional mechanical polishing and chemical etching methods, such as non-contact processing, lack of secondary contamination, and precise control of removal depth. The findings highlight the potential of this innovative approach to enhance the durability and performance of optical components in high-power laser systems, offering a promising solution to the challenges faced in laser damage mitigation.