Fourier Domain Rotational Anisotropy Second Harmonic Generation

TL;DR

This paper introduces a lock-in amplifier-based method for detecting rotational anisotropy second harmonic generation signals, enabling more sensitive and precise measurement of symmetry components in materials.

Contribution

A novel lock-in detection scheme for RA-SHG signals that improves sensitivity and allows direct Fourier component analysis of the signal.

Findings

Enhanced sensitivity over conventional methods.

Ability to measure $C_n$ symmetry components with high precision.

Validated with GaAs as a test sample.

Abstract

We describe a novel scheme of detecting rotational anisotropy second harmonic generation (RA-SHG) signals using a lock-in amplifier referenced to a fast scanning RA-SHG apparatus. The method directly measures the $n^{th}$ harmonics of the scanning frequency corresponding to SHG signal components of $C_n$ symmetry that appear in a Fourier series expansion of a general RA-SHG signal. GaAs was used as a test sample allowing comparison of point-by-point averaging with the lock-in based method. When divided by the $C_\infty$ signal component, the lock-in detected data allowed for both self-referenced determination of ratios of $C_n$ components of up to 1 part in 10$^4$ and significantly more sensitive measurement of the relative amount of different $C_n$ components when compared with conventional methods.