Laser wavelength with a ruler: easy made apparatus

We describe an easy-to-build low-cost apparatus by which the wavelength of a laser module can be determined by measuring just some lengths. The basic idea is to use a metallic workshop ruler in grazing incidence, similarly to what is done in x-ray spectrographs, where normal optical gratings are used in this configuration. We additionally propose a novel approach to the theory of the phenomenon, enabling exact calculations for a large number of diffraction maxima positions. This new scheme results in a substantial improvement in the accuracy of the calculated wavelength values compared to previous works. The apparatus has been designed for its maximum easy of construction, simplicity, availability of materials and flexibility of use. Detailed instructions on construction and alignment are given.