Optical second and third harmonic generation on excitons in ZnSe/BeTe quantum wells

TL;DR

This study investigates optical second and third harmonic generation in ZnSe/BeTe quantum wells with type-II band alignment, revealing exciton-related nonlinear optical responses and their symmetry properties under different experimental conditions.

Contribution

It demonstrates the excitation mechanisms of SHG and THG in ZnSe/BeTe quantum wells using femtosecond and picosecond laser pulses, including the magnetic field effects on SHG.

Findings

SHG is symmetry-forbidden along the growth axis but can be induced by magnetic field.

THG is observed at zero magnetic field with field-independent intensity.

Group theory analysis clarifies the excitation mechanisms involved.

Abstract

Optical harmonic generation on excitons is found in ZnSe/BeTe quantum wells with type-II band alignment. Two experimental approaches with spectrally-broad femtosecond laser pulses and spectrally-narrow picosecond pulses are used for spectroscopic studies by means of second and third harmonic generation (SHG and THG). The SHG signal is symmetry-forbidden for light propagation along the structure's growth axis, which is the [001] crystal axis, but can be induced by an external magnetic field. The THG signal is detected at zero magnetic field and its intensity is field independent. A group theory analysis of SHG and THG rotational anisotropy diagrams allows us to identify the involved excitation mechanisms.