RESUMO
In this Letter, a novel method to evaluate nonlinear refractive index using time-resolved digital holographic microscopy is introduced. To demonstrate the viability of the method, cross-correlative nonlinear refractive index values for sapphire are measured experimentally: 2.75·10-20 m2/W at 1030 nm and 4.10·10-20 m2/W 515 nm wavelengths. The obtained results for sapphire are compared to those available in literature obtained by other methods.
RESUMO
We investigate the electronic photo-excitation and relaxation mechanisms involved in the optical breakdown of potassium dihydrogen phosphate crystal (KH2PO4) and its deuterated form. The dynamics and spectroscopic properties of electron-hole pair formation are investigated using time-resolved measurement of the dielectric function, and luminescence spectroscopy. The non-common mechanical and electronic characteristics of these dielectric materials are revealed by the particular structure of ablation craters and also by the complex dynamics observed in the relaxation of excited carriers. This relaxation occurs in two steps, and varies with the initial carrier density and thus with the laser intensity. We show that the defect states play a key role in the excitation pathways, and also determine the relaxation stage. The latter also depends upon the initial amount of energy of the electron-hole pair after photo-excitation. A model based on kinetic equations describing the evolution of the different level populations allows us to successfully interpret and reproduce the experimental data.
