Femtosecond second harmonic generation and autocorrelation applications using nonlinear poled polymeric thin films

Abstract

The large second-order nonlinearities and short interaction lengths of poled polymer thin films permit unique ultrashort pulse applications. Second-harmonic generation (SHG) with femtosecond pulses requires the use of extraordinarily thin nonlinear media because of the group velocity mismatch (GVM) between the fundamental and second harmonic waves. This limitation is especially severe for the visible to UV wavelength conversions. The short interaction length of poled polymer films results in negligible pulse broadening of the fundamental and second harmonic pulses. For autocorrelation measurements, since phase matching is not a requirement, the poled films can be readily used at different wavelengths. Experimental results of a femtosecond pulse application feasibility study that uses poled polymeric thin films are presented. For example, the results of an experiment that demonstrate SHG of 14-fs long 630-nm pulses using a poled polymeric film 2.5 μm thick are presented. The efficiency is high for such a thin material: 0.16% has been measured and 0.5% has been determined to be possible. A damage threshold of ~60 GW/cm2 was observed. Since GVM is negligible in the film, this allows the generation of UV pulses as short as a few femtoseconds.