Inline LIPSS monitoring method employing light diffraction

Laser induced ripples that are also known as Laser Induced Periodic Surface Structures (LIPSS) have gained a considerable attention by researchers and industry due to their surface functionalization applications. However, texturing large areas or batch manufacture of parts that incorporate LIPSS surfaces, require the development of tools for monitoring the LIPSS generation and potentially for controlling their main geometrical characteristics, i.e. spatial periodicity, orientation and amplitude. In this context, the focus of the research reported in this paper is on developing process monitoring and inspection methods for identifying shifts and changes in these characteristics. One of the well-known and widely used by industry method for characterising and inspecting surfaces is light scattering and this research investigates the capabilities of this method for inline monitoring of LIPSS optical response. A simple setup was designed and implemented for measuring the diffraction angle and intensity of the reflected light from LIPSS surfaces. The capabilities of this concept for determining relative shifts in the optical response on surfaces processed with known disturbances such as incident angle deviations and focus offset, were investigated. Sensitivity of the method proved to be sufficient to detect shifts/deviations from LIPSS reference and thus potentially to monitor their generation inline with a simple sensor, e.g. the LIPSS treatment of larger tool surfaces or serial manufacture of holograms.