Anti-Stokes photoluminescence and Second-harmonic generation in two-tier nanolaminate plasmonic crystals.

Nanoplasmonic systems are employed to enhance nonlinear frequency conversion efficiencies at the nanoscale.  Thus, these novel material systems have a wide variety of applications in developing new light sources, ultrafast sensing, optoelectronics, and also in characterization and spectroscopy. Multiresonat plasmonic structures can achieve broadband deep-subwavelength light concentration allowing efficient multiphoton nonlinear optical processes, such as second harmonic generation (SHG) and anti-Stokes photoluminescence (ASPL). In this study, we have investigated multiresonant enhancement of SHG and ASPL emissions in an Ag-SiO₂-Ag nanolaminate array coated by TiO₂ cladding layers of 25 nm, 60 nm, and 130 nm, respectively. These two-tier nanolaminate plasmonic crystals structures offer independent control over the plasmonic modes active at excitation and emission wavelengths. We have conducted incident power, wavelength, and polarization dependence measurements of SHG and ASPL, under ultrafast NIR illumination using a Coherent Chameleon Ti:sapphire laser with a repetition rate of 80 MHz, a wavelength range from 700 -1050 nm, and a pulse width of 140 fs. Furthermore, we provide a side-by-side analysis of the observed nonlinear emission to understand the origin of the observed SHG and ASPL in these plasmonic structures.