Ultrafast nonlinear optical properties of TiO₂nanoclusters at 850 nm

Abstract

We discuss nanoclusters of titanium dioxide, bulk CdTe and CS 2 as characteristic materials to illustrate two main ideas; firstly, it is possible to argue about the origin of the nonlinearity even with a high repetition laser, provided that you have as large a peak power (50 kW) as the one found in femtosecond lasers. Secondly, the search for dimensional confinement to enhance nonlinear optical properties has experienced some difficulties with conflicting results. We show that electronic nonlinear behavior increases from TiO 2 , CS 2 to CdTe and the nonlinear thermal effect increases from CS 2 , CdTe to TiO 2 .

Spectral broadening in anatase titanium dioxide waveguides at telecommunication and near-visible wavelengths

“…Our 794-nm studies provide the first observation of spectral broadening in TiO 2 waveguides in the NVIS window. Our value of n 2 around 794 nm agrees well with most literature values for the nonlinear index of bulk and thin-film TiO 2 [31][32][33][34][35]. In addition, the wavelength-independent 2PA (7 × 10 −12 m/W) is of the same order of magnitude as that measured in bulk rutile and may pose a limit for all-optical devices around 800 nm [23,31].…”

“…Understanding the interplay between nonlinear refraction and absorption in TiO 2 is critical for all-optical devices. Our value of n 2 around 1565 nm (0.16 × 10 −18 m 2 /W) is an order of magnitude lower than typical values for TiO 2 (0.8-3 × 10 −18 m 2 /W [31][32][33][34][35]). The decreased value of n 2 at telecommunication wavelengths is consistent with theoretical models [19,20].…”

“…TiO 2 exists in several crystalline phases including rutile (E g = 3.1 eV), anatase (E g = 3.2 eV), and brookite (E g = 3.1 eV) making it ideal for wavelengths near 800 nm [29,30]. The nonlinear index of bulk and thin-film TiO 2 typically ranges from 0.8-3 ×10 −18 m 2 /W in the NVIS window [31][32][33][34][35], which is an order of magnitude greater than the nonlinear index of silica fiber (2.48 × 10 −20 m 2 /W [36]). However, values obtained from thin-films measurements have been reported as large as 5 × 10 −17 m 2 /W [37], and as small as 1 × 10 −19 m 2 /W [38] and −6 × 10 −17 m 2 /W [39].…”