Phase deflectometry is a cutting-edge optical measurement technique used for detecting defects in ultra-thin multi-layer glass structures. The system consists of a reflective light source that projects encoded sinusoidal patterns, a beam splitter that directs light to the sample surface, and a camera that captures the reflected fringe patterns. This non-contact method can detect surface deformations with nanometer-level precision.
The reflective light source generates precisely encoded sinusoidal wave patterns with specific spatial frequencies. These structured light patterns are projected onto the multi-layer glass surface. The sinusoidal encoding allows the system to measure surface height variations by analyzing phase shifts in the reflected patterns. Each layer of the glass can introduce different optical path changes, which are captured in the phase information.
The beam splitter directs the encoded sinusoidal patterns toward the multi-layer glass surface. As light interacts with each layer interface, partial reflections occur, creating complex interference patterns. Surface defects and subsurface defects cause different types of phase distortions in the reflected patterns. The deformed fringe patterns contain crucial information about defect location and depth within the glass structure.
The camera captures the deformed fringe patterns through its lens system. The image sensor records the intensity variations of the reflected sinusoidal patterns. Advanced phase extraction algorithms process these fringe patterns to generate phase maps that reveal surface height variations. Different types of defects create distinct phase signatures, allowing the system to distinguish between surface defects and subsurface defects based on their characteristic phase distortion patterns.
The final step involves comparing phase deflectometry results with line scan imaging data to classify defects accurately. Surface defects appear prominently in both phase maps and line scan images, showing high phase contrast and clear visibility. Subsurface defects are primarily detected through phase information, appearing with lower contrast in conventional imaging. This multi-modal approach enables precise defect classification, determining whether defects are located on the surface or within the glass layers, which is crucial for quality assessment and manufacturing process optimization.