Plasmon-enhanced ultrafast and tunable thermo-optic nonlinear optical properties of femtosecond laser ablated TiO2 and Silver-doped TiO2 nanoparticles

We report the results obtained from our extensive femtosecond (fs) nonlinear optical (NLO) studies of titanium dioxide (TiO2) and silver (Ag) doped titanium dioxide (Ag-TiO2) nanoparticles. TiO2 as well as Ag-TiO2 nanoparticles (NPs) were synthesized in deionized water using the techniques of fs laser ablation and simultaneous laser induced chemical reduction through irradiation, respectively. The broadband third-order nonlinear optical (NLO) behaviour of the synthesized NPs was investigated by employing the standard open and closed aperture Zscan experiments with fs laser pulses delivered from an oscillator (-80 MHz repetition rate at wavelengths of 700 nm, 750 nm, 800 nm, 850 nm) and amplifier pulses (1 kHz repetition rate at wavelengths of 800 nm, 1000 nm, 1100 nm, 1200 nm). The corresponding NLO coefficients [two-photon absorption (2PA) coefficients of -10-8 cm/W and three-photon absorption (3PA) coefficients of -10-15 cm3/W2 with MHz excitation] were retrieved from the theoretical fits to the experimental Z-scan data. It was evident from the experimental observations that the Ag-TiO2 NPs demonstrated a significant tendency towards 3PA and also crucially higher nonlinear susceptibility [chi(3)] in comparison with the pure TiO2 NPs. In this extensive investigation, not only a remarkable correlation has been established regarding the incorporation of Ag into TiO2 matrix with thermal-optic influence (MHz interaction) but also the fundamental plasmon-enhanced nonlinear absorption (NLA) in the case of 1 kHz pulse excitation has been decisively recognized. The synthesized nanocomposites were scrupulously probed in the near-IR regime, unveiling the presence of a prominent 3PA (with retrieved coefficients of -10-23 cm3/W2 using kHz excitation), an essentially rare observation in these kinds of NPs.

Automated summary

The research presents the outcomes of extensive femtosecond nonlinear optical studies on TiO2 and Ag-doped TiO2 nanoparticles. It was observed that Ag-TiO2 nanoparticles exhibited a significant preference for three-photon absorption and had a higher nonlinear susceptibility compared to pure TiO2 nanoparticles under 1 kHz pulse excitation. Additionally, the synthesized nanocomposites showed a noteworthy presence of three-photon absorption in the near-IR regime, which is a rare observation in these types of nanoparticles.