The spreading of laser beams due to diffraction is a fundamental physical consequence of wave optics governed by the wave nature of light, making it a matter of everyday observation and textbook physics that requires no citation.
The claim states that laser beams diverge due to the laws of diffraction, which is a foundational physical fact inherent to wave propagation and optical physics. None of the retrieved papers specifically evaluate or test this basic premise as a novel hypothesis; instead, papers mention diffraction as a measurement tool or standard optical property (e.g., papers 0, 6, 9). Because this relationship is a direct consequence of wave mechanics and everyday optical observation, it is categorized as common knowledge requiring no citation.