O espalhamento Raman correlacionado Stokes-anti-Stokes: um estudo da influência da largura temporal do pulso de excitação

Abstract

In this work, we study the correlated Stokes-anti-Stokes (SaS) Raman scattering in a diamond sample and the influence that the excitation pulse width has in the intensity of generation of the correlated pairs in the process. For this investigation, we used two excitation systems with different temporal pulse width, one with femtosecond temporal width and one with picosecond temporal width. We did two distinct experiments with this excitation systems with difference in the way of filtering the signal: In the first experiment, the signal filtering is made with band-pass filters, this configuration has a greater efficiency that allow us compare better the correlated pair formation efficiency between the different excitation systems. In the second experiment, we used a monochromator to filtering the signal, this configuration allow us to change the wavelength of the detection so we can measure the formation spectrum of the correlated pairs. The results obtained from these experiments show us that the correlated pairs generation efficiency is larger with the use of the system with femtosecond temporal width, what is expected for a non-linear process. In the resonant Raman frequency region, we observed a intensity 1.5 times larger with the use of femtosecond system, and in the out-of-ressonance Raman region, we observed a intensity 5 times larger in the region with lowest Raman shift and 9 times larger in the region with largest Raman shift. We also measure the formation pairs spectrum around the first order Raman peak of the diamond, confirming the existence of a asymmetry in the formation of this pairs with respect to the positive versus negative detuning from phonon resonance. This asymmetry still remains without a satisfactory theoretical explanation.