Abstract: This paper addresses students′ common difficulties in understanding the connection between the high directionality of lasers and their spatial coherence. It systematically analyzes the fundamental differences between conventional incoherent light sources and laser sources in terms of coherence and directional properties. By comparing theories of spatial coherence in physical optics and laser principles, the distinctions and intrinsic relationships between these concepts are clarified, providing theoretical support for students to gain a deeper understanding of the "four key characteristics" of lasers.

Key words: laser directionality, spatial coherence