Detection of the laser induced damage using a He-Ne laser reflective imaging technique

Reduction of the laser-induced damage is a serious challenge for optical components; therefore, determining the laser-induced damage threshold (LIDT) is a crucial step in the manufacturing process. This article introduces a He–Ne laser imaging system designed for in-situ damage detection within a LIDT station. The system provides fourfold-magnified imaging of the test sample and its surroundings, capturing the damage shape and size without requiring any imaging optics to be placed inside the vacuum chamber. This design helps maintain the cleanliness of the chamber. The detection method can be applied to both transparent and opaque samples; in transparent optics, damage is observable from either side and it can be distinguished at which side damage developed. To verify the system’s functionality, two sample types were investigated: a silica wafer (non-transparent for He–Ne radiation) and a commonly used double coated anti-reflective (AR) window for 1030 nm (transparent for He–Ne radiation). Particular attention was devoted to determining the minimum damage size that can be reliably recognized. The system successfully distinguished damage features as small as 35 μm.