Fourier domain rotational anisotropy-second harmonic generation

Area of Science:

• Nonlinear Optics
• Materials Science
• Surface Science

Background:

• Rotational anisotropy-second harmonic generation (RA-SHG) is a surface-sensitive technique.
• Accurate detection of RA-SHG signals is crucial for characterizing material symmetries.
• Existing methods for RA-SHG signal analysis can be limited in sensitivity and self-referencing capabilities.

Purpose of the Study:

• To develop a novel and highly sensitive method for detecting RA-SHG signals.
• To enable self-referenced determination of different symmetry components within RA-SHG signals.
• To compare the performance of the new method with conventional point-by-point averaging techniques.

Main Methods:

• Implementation of a lock-in amplifier referenced to a fast scanning RA-SHG apparatus.
• Direct measurement of the nth harmonics of the scanning frequency to isolate SHG signal components.
• Utilizing Fourier series expansion to analyze general RA-SHG signals.

Main Results:

• The lock-in based method directly measures SHG signal components corresponding to Cn symmetry.
• Self-referenced determination of Cn component ratios with precision up to 1 part in 10^4 was achieved.
• The new method demonstrated significantly higher sensitivity in measuring relative amounts of different Cn components compared to conventional methods.

Conclusions:

• The developed lock-in amplifier scheme provides a robust and sensitive approach for RA-SHG signal detection.
• This method offers improved accuracy and self-referencing capabilities for analyzing material symmetries.
• The findings pave the way for more precise characterization of surfaces and interfaces using nonlinear optical techniques.