Using a monochromatic plane wave to generate periodic arrays of metallic nanoparticles with tunable features buried in thin films is the original work we report here. We focus on the way such waveguiding metallic photonic crystals can self-emerge from thin films homogeneously loaded with metallic precursors under continuous-wave and homogeneous laser excitation. This paper fully describes the conditions leading to the formation of periodic structures and highlights the role of several parameters in the underlying physical mechanisms. The laser exposure parameters, especially, fix the geometrical and optical properties of the generated structures. Grating lines are parallel to the laser polarization and the period is directly linked to the laser wavelength. Both electron resonances of metal nanoparticles and optical resonances of guided modes interact to form the periodic patterns under homogeneous exposure. A model, based on the coupled mode theory, can be proposed to predict the spontaneous generation of such periodic nanostructures. It concludes that the guided waves exponentially enhance during illumination due to a positive feedback loop with the ordered growth of particles. This process opens up new fabrication techniques for making optical devices and may find applications in various fields such as polarization imaging, displays, security or lighting.