Third-order nonlinear optical responses of Cr3+ ions on La2(WO4)3 nanoparticles for optical limiting applications

Abstract

In this article, we discuss the nonlinear optical limiting characteristics of pure and Cr3+ doped La2(WO4)3nanoparticles using soft chemical method. We studied the third-order nonlinear optical properties of nanoparticle using a continuous-wave (CW) laser system pumped by a diode laser at 785 nm. The results reveal that the materials possess reverse saturable absorption (RSA) and self-defocusing in nature. Due to the presence of near-resonant excitation state, the material exhibits sequential two-photon absorption (excited state induced thermally) process. We observe a higher non-linear absorption coefficient (β) and nonlinear refractive index (n2) for 0.7 % Cr3+ doped La2(WO4)3 systems which is higher than that of pure La2(WO4)3 nanoparticles. The transmittance decreases with increased input fluence for both pure and Cr3+ doped La2(WO4)3 samples exposing the optical limiting behavior of the prepared sample. The presence of larger concentrations of more polarizable Cr3+ ions, increased density of states, and higher oxygen defects resulted in enhanced OL behaviour for 0.7 % Cr3+ doped La2(WO4)3 sample. It is found that two photon absorption (β) is increased from 0.41 to 1.16 × 10-3 and third order nonlinear susceptibility (χ(3)) enhances from 3.909 x10-6 to 6.696 × 10-6 esu on Cr doping. The optical limiting threshold of pure and CrxLa1-xWO4 nanoparticles was also studied and found to be in the range of 91.2 to 86.2 W/cm2. As a consequence of the obtained results Cr3+ doped La2(WO4)3 is likely to be an appropriate candidate for CW low-power optical limiting (OL) applications.