Polarized second-harmonic measurements with broadband femtosecond sources

摘要

Sensitive second-harmonic polarization measurements can yield important information about the symmetry properties of thin films. When the linewidth of the probe laser is relatively narrow, as in the case of a nanosecond pulse from a Nd:YAG laser, the polarization-sensitive optical components, waveplates in particular, behave according to specifications. However, the question arises, does this case also apply to a broadband source, such as a femtosecond laser pulse, where the linewidth is much greater than that of the waveplate? We show that the case does indeed hold by comparing measurements using both sources. However, special attention must be focused on the performance of the optics themselves, as manufacturer's specifications may not be accurate for each individual piece. The agreement of the measurements opens the door for determining the symmetry properties of completely new types of low-symmetry samples, such as gold nanoparticle arrays, which must be studied with a femtosecond source to avoid damaging the particles.