Second harmonic generation from nanocrystals under linearly and circularly polarized excitations

Area of Science:

• Nonlinear optics
• Materials science
• Nanophotonics

Background:

• Second harmonic generation (SHG) is a key nonlinear optical process.
• Understanding SHG in nanocrystals is crucial for applications in imaging and photonics.
• The polarization dependence of SHG from nanocrystals requires further theoretical and experimental investigation.

Purpose of the Study:

• To develop theoretical models for SHG from non-centrosymmetric nanocrystals.
• To investigate the effect of excitation polarization (linear vs. circular) and focusing on SHG.
• To experimentally verify the theoretical predictions using barium titanate (BaTiO3) nanocrystals.

Main Methods:

• Development of theoretical models for SHG under plane-wave and focused excitations.
• Numerical simulations to analyze polarization dependency.
• Experimental measurements of SHG polar responses using a scanning confocal microscope.

Main Results:

• Focused excitation significantly reduces the polarization dependency of the SHG signal.
• Circularly polarized excitation generally results in a weaker SHG response compared to the average of linearly polarized excitations.
• Experimental SHG polar responses from BaTiO3 nanocrystals closely match theoretical predictions.

Conclusions:

• Theoretical models accurately describe SHG from nanocrystals.
• Focused excitation offers a method to control SHG polarization sensitivity.
• The findings provide insights into optimizing SHG for nanocrystal-based photonic devices.