38 - Expression of optical function by nanostructure using femtosecond laser processing

Abstract

This chapter presents various femtosecond laser-induced phenomena in glasses for expressing optical functions by nanostructures. Space-selective room temperature permanent photoreduction of rare-earth ions of Sm3+ to Sm2+ in borate and other glass samples by an infrared femtosecond laser is observed. The results demonstrated the possibility of selectively inducing a change of valence state of Sm3+ ions on the micrometer scale inside a glass sample by using a focused nonresonant femtosecond pulsed laser. This technique is useful in the fabrication of three-dimensional optical memory devices with high storage density. Femtosecond laser-photoreduced Sm3+-doped glasses exhibited a photochemical spectral hole burning memory property, where the microspot induced by the focused femtosecond laser inside a glass sample can be used to store data information via the irradiation of laser light with different wavelengths. The three-dimensional precipitation and control of nanoparticles in materials by using focused femtosecond laser irradiation and successive annealing are also presented, which show that the size distribution of nanoparticles can be controlled by the laser irradiation conditions. This method is useful in various practical applications such as three-dimensional optical memory, fabrication of integrative all-optical switches, controling nucleation, and crystal growth processes. The emergence of periodic structurally changed regions of nanometer size inside silica glass after irradiation by intense femtosecond light pulses is demonstrated, which can be interpreted in terms of interference between the incident light field and the electric field of bulk electron plasma density wave, that results in periodic modulation of electron plasma concentration and permanent structural changes in the glass