High-speed and efficient control of refractive index change of fused silica by multiwavelength excitation process using F_2 and KrF excimer lasers

摘要

A multiwavelength excitation process using F_2 and KrF excimer lasers for high-efficiency and high-speed refractive index modification of fused silica is demonstrated. We find that this process is essentially superior to conventional single-wavelength F_2 laser processing. The multiwavelength excitation process achieves twice of diffraction efficiency compared with that of single-wavelength F_2 laser irradiation sample at the same number of total photons supplied to the sample. This high-speed and high-efficiency modification is realized within +-50 ns of the delay time of each laser beam irradiation. In addition, the refractive index change of the multiwavelength sample was increased to 8.2x10~(-3), which is 1.78 times larger than that of single-wavelength F_2 laser irradiation sample at same irradiation time. This superiority of the multiwavelength excitation process is attributed to resonance photoionization-like process based on excited state absorption in fused silica.