High-efficiency refractive index modification of fused silica by F2 and KrF excimer laser multiwavelength excitation process

Novel materials processing by a multiwavelength excitation process using F2 and KrF excimer lasers for highefficiency and high-speed refractive index modification of fused silica is demonstrated. We find that this process is essentially superior to single-wavelength F2 laser processing. The multiwavelength excitation process achieves twice of diffraction efficiency compared with that of single F2 laser irradiation sample at the same number oftotal photons supplied to the sample. This high-efficiency and high-speed modification is realized within ns ofthe delay time ofeach laser beam irradiation. In addition, the refractive index change of the multiwavelength sample was increased by 8.2x 1 O3, which is 1 .78 times larger than that of single wavelength F2 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.