We present optical field distributions and nanohole patterning properties on a silicon substrate when a femtosecond laser is irradiated obliquely to a two-dimensional (2D) gold nanoparticle array on a silicon surface. It is necessary to control plasmon polaritons in a gold nanoparticle array by adjusting interparticle distance and the incident angle of the laser for uniform nanohole patterning with an 800nm femtosecond laser. The uniform 2D nanohole patterning is studied by finite-difference time-domain (FDTD) calculation and experiment using a femtosecond laser. Using an array with gold particles of 200nm diameter, the near-field intensity on the Si surface is much larger than that of a single isolated particle if the interparticle distance is larger than 200nm and the incident angle is approximately 50°. The oblique irradiation of p-polarized incident laser to the surface of the substrate ensures that uniform nanohole array patterning is achieved.
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