Harmonic generation in interfaces with femtosecond pulses: Nonlinear processes and pulse spectral band influence.

Abstract

The frequency conversion using nonlinear optical processes has been extensively studied under fundamental and application point of view since the laser was developed. More recently, with ultrafast pulses advances, the nonlinear optical phenomena is even more easily observed and studied. One of the fundamental femtosecond (fs) ultrashort pulse properties is the short time duration, but we need to highlight the high intensity and broad spectral range. Such properties can be explored on different applications like the new frequency generation and pulse shaping technique base on the high peak power and pulse spectral band, respectively.In this project we present some proposal to study the effect of the fs pulses on frequency conversion in different material and different interfaces. The study of the interfaces was motivated due to recent results obtained on third-harmonic generation (THG) on interfaces. We have observed that the pulse intensity and spectrum affect the THG signal. But, some of these results were not completely explained. Our first studies of the THG using Z-scan technique with fs pulses show interesting spectral interference effects due to the broad spectrum of the fs pulses, as well, we observed interfaces contribution on this third-order process. We believe that, at some extent, these effects also occur on other nonlinear processes and take place on different experimental techniques besides the THG Z-scan technique. As we know, the Z-scan technique is widely used to investigate the absorcive and refractive nonlinearities in different type of materials due to their simplicity and precision, but there are other important experimental techniques which can give complementary information which Z-scan cannot supply. Among other techniques we intend to use noncollinear THG, high-harmonic generation, four-wave mixing, etc. We believe that these investigations of nonlinear processes in the interfaces with different techniques looking at the intensity and spectrum will open a new research field for fundamental understanding and materials characterization. Furthermore, we intend to investigate the spectral phase influence using pulse shaping techniques.