Photorefractive Excitation of FF-SH Surface Plasmon Polariton Waves by femtosecond pulses at metal-nonlinear medium interfaces

S urface Plasmon Polaritons (SPPs) hold significant potential for technological applications due to their unique capability to confine electromagnetic energy at subwavelength scales. To enable advanced photon-ic integration that can rival electronic systems, operation at shorter wavelengths—particularly in the violet or ultraviolet spectral regions—is highly desirable. However, the practical implementation of SPPs at these wave-lengths is hindered by substantial absorption losses in the metallic layers required to support their propaga-tion. This study investigates a novel approach to overcoming these limitations by leveraging the nonlinear interac-tion between co-propagating SPP modes at different wavelengths. Specifically, an infrared (IR) SPP wave at 1064 nm is launched along the interface between a metal film and a nonlinear crystal. Through the substrate’s nonlinear optical response, this IR wave generates a second harmonic signal at 532 nm. Remarkably, the sec-ond harmonic propagates as an SPP over a distance approximately 30 times greater than what is typically achievable for a standalone 532 nm SPP mode. This result demonstrates a promising strategy for extending the propagation length of short-wavelength SPPs via nonlinear coupling with longer-wavelength signals.