Experimental and theoretical study of the structural parameters impacts on the thermal relaxation of nano-composites after femtosecond laser pulses
The goal ofthis thesis is to study the structural parameters' impact on the thermal relaxation of nano particles embedded in a dielectric matrix. The first part of the thesis focuses on the realization of a time domain thermoreflectance pump-probe experiment, where a Ti:Saphir laser delivers 100 fs pulses with a repetition rate of 80 MHz. This experiment is used to investigate the evolution of transmission or reflection coefficient of nanometric sized samples. Our experimental setup can detect relative variations as high as 10-7. ln the second part, we present the realization and structural characteristics ofthe samples that are made of gold or silver nano particles. In these samples, the small particles are spheres and the larger ones are roller-like. The radius of the particles varies from 2,2 nm to 10 nm, their organization is isotropic or in lines, and the number of layers differs from one sam pie to the other. The last part of the thesis focuses on the experimental results obtained and their comparison to theoretical results of a two temperature model. The different samples were compared in order to emphasize the impact of different structural parameters such as: shape, size and organization of the particles and the metal or matrix used.