Experimental evidence of asymmetrical spectrum broadening in a heavy-metal oxide glass doped with silver nanoparticles

An experimental evidence of asymmetric spectral broadening due to the presence of silver nanoparticles (NP) in composites based on WO₃ host glass and numerical calculations to support this observation, are reported. Linear and nonlinear properties of the composite are evaluated using the Maxwell-Garnett model, which exhibits a strong wavelength dependence of the effective nonlinear coefficient that determines the shape of the spectral broadening and leads to a blue spectral shift. Results also show that a short-wavelength extension of the spectrum originates from the enhancement of the nonlinearity as the wavelength approaches the plasmon resonance in accordance to the theoretical prediction, and long-wavelength lower shoulder of the spectrum arises from the stimulated-Raman-self-frequency shift.