Experimental results of second-harmonic generation from a polyurethane waveguide on a silver grating coupler

Area of Science:

• Nonlinear optics
• Plasmonics
• Materials science

Background:

• Second-harmonic generation (SHG) is a key nonlinear optical process.
• Surface plasmons and guided modes can enhance light-matter interactions.
• Grating structures enable efficient coupling of light to plasmonic and guided modes.

Purpose of the Study:

• To investigate second-harmonic generation (SHG) in a polyurethane-coated silver grating coupler.
• To study the spectral dependence of SHG efficiency by varying pump wavelengths.
• To analyze the influence of electromagnetic resonance and material absorption on SHG.

Main Methods:

• Fabrication of a silver grating coupler coated with polyurethane.
• Excitation of guided modes and surface plasmons using two different pump wavelengths (1064 nm and 1319 nm).
• Measurement of second-harmonic efficiency as a function of incident angle.

Main Results:

• A significant enhancement in SHG efficiency was observed for the 1319 nm pump wavelength near electromagnetic resonance.
• For the 1064 nm pump, the generated second-harmonic light fell within the polyurethane absorption band.
• Unexpected minima in SHG efficiency were observed for the shorter wavelength, deviating from resonance predictions.

Conclusions:

• The spectral dependence of SHG is strongly influenced by the interplay between electromagnetic resonance and material absorption.
• Polyurethane coating affects SHG performance, particularly when the generated light overlaps with the polymer's absorption spectrum.
• This study highlights the importance of considering material properties in plasmon-enhanced nonlinear optical devices.