Laser-induced damage of sol–gel SiO 2 antireflection coatings remains a key reliability issue in high-power laser systems because porous networks, residual hydroxyl groups, and defect-related absorption centers can trigger localized heating and stress concentration under nanosecond irradiation. In this work, continuous-wave CO 2 laser conditioning was used as a localized post-treatment method to regulate the microstructure of sol–gel SiO 2 coatings on fused silica substrates. The revised manuscript clarifies the processing window, scanning parameters, laser damage testing protocol, and the sample-specific nature of the reported LIDT values. Laser conditioning induces partial densification of the porous coating, dehydration of Si-OH groups, relaxation of the Si-O-Si network, and enhancement of mechanical properties. Under the optimized conditioning condition, the surface roughness decreases from 14.08 nm to 9.76 nm, and the LIDT at 1064 nm increases from 4.8 J/cm 2 to 7.0 J/cm 2. The LIDT values are discussed as a relative microstructure–property comparison for the present coating system rather than as the upper technological limit of sol–gel silica coatings. Combined FTIR analysis, thermal simulation, morphology observation, and damage probability analysis indicate that the improvement originates from the combined effects of reduced defect absorption, moderated porosity, improved heat dissipation, and enhanced resistance to thermally induced cracking. The results provide a mechanism-guided strategy for using CO 2 laser conditioning to tune sol–gel silica coatings while also identifying the need for further validation on higher-LIDT coatings and at application-relevant wavelengths. 5. Conclusions This work investigates CO 2 laser conditioning as a localized post-treatment strategy for regulating the microstructure and damage resistance of sol–gel SiO 2 coatings. The LIDT at 1064 nm increases from 4.8 J/cm 2 to 7.0 J/cm 2 under the optimized conditioning condition, corresponding to an improvement of approximately 46% within the present coating system. The revised manuscript clarifies that the absolute LIDT values are lower than those of highly optimized facility-grade sol–gel coatings and should therefore be interpreted as a sample-specific demonstration of the microstructure–property relationship rather than a technological upper limit. CO 2 laser conditioning induces partial densification of the porous network, dehydration of Si-OH groups, suppression of defect-related absorption, and enhancement of mechanical stability. These changes collectively reduce local hot-spot formation, improve heat dissipation, and increase resistance to thermally induced cracking. The results reveal that laser damage resistance is governed by the coupling among porosity, defect absorption, thermal transport, and mechanical response and that an optimal porosity regime rather than maximum densification is required. The major contribution of the work is the demonstration of a localized post-treatment methodology for regulating coating microstructure and damage precursors. Future studies should verify the approach on facility-grade high-LIDT sol–gel coatings and under application-relevant wavelength, pulse-duration, and beam-size conditions.
