Using a diffraction grating and a ruler to measure the wavelength of a laser pointer is a standard physics demonstration and everyday laboratory procedure that requires no formal citation.
The claim describes a standard, fundamental physics laboratory procedure for measuring light wavelength using diffraction grating equations (d sin theta = n lambda), where distances are measured with a ruler. As a matter of basic physics and direct everyday educational observation, this is common knowledge and does not require literature citation, nor do the retrieved technical papers address this specific pedagogical experiment.