Strong third-and higher-order nonlinear optical studies on femtosecond laser ablated Germanium metalloid nanoparticle colloid in the wide spectral domain (450–1500 nm)

Abstract

Wide spectral region higher-order optical nonlinearities are hereby reported for ultrashort pulsed laser ablated germanium nanoparticle (Ge NPs) colloidal solutions. The Ge NPs colloids are studied for optical nonlinearities under a wide spectral domain (∼450–1550 nm) utilizing the femtosecond laser (120 fs, 1 kHz) pulses. The results of the nonlinear absorption indicate a strong dominance of multi-photon absorption phenomena (two-, three- and four-photon absorptions), involving band-to-band and defect induced energies of the quantum confined Ge NPs. The intensity-dependent [(4–8) × 1015 W m−2] nonlinear absorption exhibits a monotonically decremental trend with the increase in excitation intensity, suggesting the involvement of higher-order nonlinear optical effects. Moreover, the obtained presented results also depict strong nonlinear contribution evidenced by two orders of higher magnitude nonlinear refraction in the infrared (IR) region, 1000–1550 nm. The enhanced optical nonlinearities in the IR region propound the capabilities of these Ge NPs as a potential substitute for silicon in IR photonics-related applications.