Polycrystalline materials plays a crucial role in the production of optical components due to its wide range of applications. However, the presence of irregular micro-structures (IMS) on the machined surface poses challenges to achieving high-quality results in SPDT. Understanding the underlying mechanism responsible for the formation of these IMS is therefore essential for obtaining superior machined surfaces in polycrystalline copper. In this chapter, a comprehensive theoretical and experimental investigation is conducted to unravel the generation mechanism of IMS.