Automated polarization control for application in time-resolved second harmonic generation experiments

Rotational anisotropy second harmonic generation (RA-SHG) is a non-linear optical technique used to probe condensed matter systems. In order to fully fit the independent components of the SHG susceptibility tensor, both S and P polarized input and output combinations need to be measured, meaning that the incoming and outgoing polarizers need to be physically rotated to realize all the physically meaningful polarization combinations. However, doing this rotation manually takes time and adds significant labor costs to taking data, especially when taking time-resolved data. We implement automated polarization rotators for use in time-resolved RA-SHG, in order to improve the technique’s robustness to low-frequency noise. Instead of sweeping the polarizations sequentially, automated polarization rotation allows for repeatedly toggling between polarization combinations, allowing averaging of a particular polarization combination over long timescales. These polarization rotators utilize small stepper motors within the rotating RA-SHG setup and demonstrate high fidelity in time-resolved RA-SHG experiments. We show this system's functionality in time-resolved RA-SHG in the test-sample GaAs.