Strong nonlinear optical processes with extraordinary polarization anisotropy in inversion-symmetry broken...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Photonics

Background:

• Nonlinear optical (NLO) activities, particularly second harmonic generation (SHG), are crucial in two-dimensional (2D) transition metal dichalcogenides (TMDCs) lacking inversion symmetry.
• Anisotropic NLO processes are vital for developing polarization-controlled nano-nonlinear photonic devices, a key research area in nonlinear photonics.
• A significant challenge in 2D materials is the simultaneous presence of strong nonlinearity and pronounced optical anisotropy.

Purpose of the Study:

• To investigate the nonlinear optical properties of even-layer Palladium Phosphoselenide (PdPSe).
• To explore the potential of PdPSe for applications requiring strong and tunable nonlinear optical responses with high anisotropy.
• To demonstrate the utility of PdPSe's unique NLO characteristics in advanced imaging and encoding techniques.

Main Methods:

• Experimental characterization of second-order and third-order nonlinear optical susceptibilities in even-layer PdPSe.
• Measurement and analysis of second harmonic generation (SHG) anisotropy, including its dependence on excitation wavelength.
• Demonstration of polarized SHG imaging for crystal orientation identification and polarization-dependent spatial encoding.

Main Results:

• Even-layer PdPSe exhibits strong second-order (64 pm/V) and third-order (6.2×10^-19 m²/V²) nonlinear optical susceptibilities.
• PdPSe demonstrates remarkable SHG anisotropy with a ratio of ~45, the highest reported for 2D materials, and this ratio is tunable (0.12 to 45) with excitation wavelength.
• Successful demonstration of polarized SHG imaging for crystal orientation and polarization-based spatial encoding.

Conclusions:

• Even-layer PdPSe possesses superior nonlinear optical properties and strong SHG anisotropy, surpassing common TMDCs.
• The tunable SHG anisotropy in PdPSe offers significant advantages for designing advanced nanophotonic devices.
• PdPSe is a promising material for next-generation nonlinear nanophotonics and optoelectronics, enabling applications in imaging and data encoding.