We study the process of laser-induced periodic structures on the surfaces of iron materials with prefabricated structures and investigate the role of the periodic energy distribution generated by surface plasmon polariton (SPP) interference in this process. The finite difference time domain method is used to simulate the electromagnetic field distributions on the surfaces of iron materials with gratings, rectangular arrays, and pyramid array structures when the laser is incident. The influences of parameters such as the period, height, and shape of the prefabricated structure on the energy distribution on the material surface are discussed. When the prefabricated structure satisfies the SPP interference enhancement condition, a strong periodic electromagnetic field energy distribution appears on the material surface, resulting in laser-induced periodic surface structures (LIPSS). The results of this study can provide theoretical guidance for the laser micro/nano processing of metal materials.

The finite time difference method is used to study the influence of prefabricated structures on the LIPSS, and models of grating structures, rectangular array structures, and pyramid array structures are established for the simulation. The influence of surface-prefabricated structures on the distributions of electromagnetic fields on the material surfaces as well as the regulation of LIPSS is also studied. Simultaneously, the evolution process of LIPSS is also simulated.

A series of electric dipoles on the surfaces of metal materials can achieve the directional coupling of surface plasmon polarons and thereby generate plane waves. In the previous section, the simulated prefabricated structure array plays a role similar to that of an electric dipole array. When the laser is incident on a column of prefabricated structures perpendicular to the direction of laser polarization, coupling occurs between the SPPs excited by each structure, thereby resulting in plane waves propagating along the direction of laser polarization. The sidewall and substrate interface of each individual prefabricated structure becomes a scattering center, and the excited SPPs can propagate outward and interfere with each other. Each column of the prefabricated structure array generates plane waves that propagate along the direction of laser polarization owing to SPP coupling.

When the prefabricated structure is a rectangular array and the period of the prefabricated structure is even times the half wavelength of the laser along the direction of laser polarization, the SPP interference is enhanced, the electromagnetic field energy amplitude is large, and obvious periodic fringes can be obtained. When the period of the prefabricated structure array is odd times the half wavelength of the SPP, the interference of the SPP is cancelled, and the amplitude of the electromagnetic field energy is small, making it difficult to observe periodic fringes (Fig. 8). If the period of the prefabricated structure is large in the direction perpendicular to laser polarization direction, periodic fringes cannot be obtained (Fig. 9). If the height of the prefabricated structure is excessively large, periodic stripes cannot be obtained (Fig. 10).When the prefabricated structure is a four-pyramid column and the period of the prefabricated structure array is odd times the half wavelength of the laser along the direction of laser polarization, the SPP interference is enhanced, the electromagnetic field energy amplitude is large, and obvious periodic fringes can be obtained. When the period of the prefabricated structure array is even times the half wavelength of the SPP, the interference of the SPP is cancelled, and the amplitude of the electromagnetic field energy is small, making it difficult to observe periodic fringes (Fig. 11).

This study investigates the energy distributions on the surfaces of iron materials with prefabricated structures under 355 nm laser irradiation. When the width of the grating structure groove or the period of the two-dimensional prefabricated structure array satisfies the SPP interference enhancement condition, a periodic energy distribution is observed on the material surface. If the energy of the SPP interference-enhancement region exceeds the ablation threshold of the material, laser-induced periodic surface structures are formed on the material surface via ablation. The regularity of the LIPSS formed by direct laser irradiation of the material surface is relatively low. The regularity of the LIPSS can be increased by preparing specific prefabricated structures on the material surface. The material surface energy can be modulated by changing the height of the prefabricated structure, resulting in LIPSSs at different depths.