Enhanced surface second harmonic generation in nanolaminates.

Area of Science:

• Nonlinear Optics
• Materials Science
• Surface Science

Background:

• Second-harmonic generation (SHG) is a nonlinear optical process forbidden in centrosymmetric media.
• Surface SHG occurs due to broken inversion symmetry but is typically weak.
• Periodic dielectric multilayers offer numerous surfaces for potential SHG enhancement.

Purpose of the Study:

• To experimentally investigate and enhance surface SHG using periodic dielectric multilayer stacks.
• To explore the feasibility of fabricating ultrathin dielectric layers for SHG applications.
• To determine the dependence of SHG on multilayer structure and angle of incidence.

Main Methods:

• Fabrication of alternating SiO2/TiO2 multilayer stacks using Plasma Enhanced Atomic Layer Deposition (PEALD).
• Achieved individual layer thicknesses below 2 nm.
• Experimental measurement of SHG at large angles of incidence (> 20 degrees).

Main Results:

• Demonstrated substantially enhanced surface SHG from periodic multilayer structures.
• Observed SHG levels significantly exceeding those from simple interfaces.
• Experimental results show good agreement with theoretical calculations for varying periods and thicknesses.

Conclusions:

• Periodic dielectric multilayers are effective for significantly enhancing surface SHG.
• PEALD enables precise fabrication of ultrathin layers crucial for this enhancement.
• This approach provides a pathway for developing novel nonlinear optical devices.