In this paper, we performed a detailed study of the formation of femtosecond laser-induced periodic surface structures (LIPSSs) on platinum and gold at near-damage threshold fluences. We find a unique type of LIPSS entirely covered with nanostructures. A distinctive feature of the nanostructure-covered LIPSS is that its period is appreciably less than that of the regular LIPSS. We show that the reduced period is caused by an increase of the real part of the effective refractive index of the air-metal interface when nanostructures develop and affect the propagation of surface plasmons.

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By applying the femtosecond laser blackening technique directly to a tungsten incandescent lamp filament, we dramatically brighten the tungsten lamp and enhance its emission efficiency to approach 100%. A comparison study of emission and absorption for the structured metal surfaces shows that Kirchhoff's law is applicable for the black metal. Furthermore, we demonstrate that we can even obtain partially polarized light as well as control the spectral range of the optimal light emission from the laser-blackened tungsten lamp.

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