Polarization- and time-resolved nonlinear multi-photon spectroscopy for confocal microscopy of semiconductor nanostructures

TL;DR

This paper introduces a versatile confocal microscopy system capable of polarization-resolved, time-resolved multi-photon spectroscopy for studying semiconductor nanostructures with high spatial, spectral, and temporal resolution.

Contribution

The authors develop a comprehensive confocal microscopy setup with polarization control, broad spectral tunability, and cryogenic and magnetic field capabilities for advanced nonlinear optical studies.

Findings

Demonstrated polarization tomography on Cu₂O crystal

Performed wide-range SHG spectral scans on ZnSe

Mapped twisted MoS₂ structures with polarization sensitivity

Abstract

We present a versatile confocal microscopy setup for optical second harmonic generation (SHG) and multi-photon spectroscopy that enables polarization-resolved studies of semiconductor bulk crystals and low-dimensional structures. The system offers full polarization control in both excitation and detection, spatial scanning with micrometer resolution, and spectrally tunable excitation over a broad energy range from 0.5 to 4.0 eV, using femtosecond and picosecond laser pulses. Samples are mounted in a helium-flow cryostat, allowing temperature control from 4 to 300 K. Magnetic fields up to 0.625 T can be applied in the Voigt geometry via an electromagnet. The nonlinear optical signals are analyzed using a high-resolution spectrometer with a spectral resolution of 60 $\mu$eV. We demonstrate the potential of the setup by means of SHG polarization tomography measurements on a Cu$_2$O crystal as well as through a SHG spectral scan of a ZnSe crystal over a wide energy range from 1.4 to 3.1 eV. Polarization-resolved confocal SHG mapping of various twisted mono- and bilayer MoS$_2$ structures is also presented. In addition, time-resolved two-color pump-probe experiments are shown for a Cs$_2$AgBiBr$_6$ crystal, illustrating the potential of the system for investigating coherent exciton and phonon dynamics.