Narrow Results

Saturable absorbers and optical limiters have contrary optical transmission properties. We report observations of simultaneous occurrence of both these effects in a nickel sulfide nanoparticle (average diameter ~5 nm) solution and a simultaneous quantitative measurement of both. Intensity-dependent nonlinear transmission studies carried out using a 7 ns Nd:YAG laser at 532 nm by the Z-scan method, revealed efficient optical limiting in nickel sulfide nanoparticle suspensions. Induced nonlinear optical scattering was identified to be the mechanism of optical limiting, and absorption at 532 nm was found to saturate. A modification of the conventional Z-scan implementation led to the retrieval of the saturation intensity, which is otherwise overshadowed by very strong nonlinear scattering.

Two-photon optical nonlinear absorption has been studied in quantum dots of CdS_xSe_1-x grown in borosilicate glass matrix by two-step annealing technique. Femtosecond laser and open aperture Z-scan technique has been used for measuring the third-order nonlinear two-photon absorption coefficient (β⁽³⁾). Only the third-order and not the fifth-order nonlinear effects are observed at low intensities (1.6–3.2 GW cm^-2) of laser used in the present experiment. At such low intensities, the variation of β⁽³⁾ is found to be almost intensity-independent. For a given annealing duration of the quantum dots, the value of β⁽³⁾ is found to be higher for sulfur-rich samples as compared to that for selenium-rich samples. This is attributed to the presence of shallow traps formed due to sulfur vacancies in the sulfur-rich samples. Further, the value of β⁽³⁾ increases with the increase in the size of quantum dots and the rate of increase of β⁽³⁾ with the increase of average radius is found to be higher for sulfur-rich samples.

The paper was retracted as the authors have submitted the same manuscript to two completely different journals, which is seriously academic fraud and against academic ethics.

Nanostructured nonlinear optical (NLO) materials are attracting increasing interest as optical limiters for various applications. In this study, one-dimensional nanostructured Na₂Ti₃O₇ was synthesized by a typical hydrothermal method and systematically characterized. The results showed that one-dimensional nanostructured Na₂Ti₃O₇ has good crystallinity and thermal stability. Its morphology can be easily controlled to form nanotubes, nanobelts and nanorods by altering the amounts of added NaOH. The robustness of the NLO properties of one-dimensional nanostructured Na₂Ti₃O₇ in broadband optical limiting (OL) applications was investigated by the open-aperture Z-scan method. At laser wavelengths of 532 nm and 1064 nm, the effective nonlinear extinction coefficients showed nonmonotonic dependence on the morphology; nanotubes gave the maximum value. The results confirmed that the NLO and OL responses of one-dimensional nanostructured Na₂Ti₃O₇ can be effectively optimized by tailoring the morphology. In addition, the nonlinear extinction coefficients of these three types of one-dimensional nanostructured Na₂Ti₃O₇ are better than those of multi-walled carbon nanotubes, a benchmark one-dimensional OL material, at 532 nm and 1064 nm; they therefore have potential applications in nonlinear optics. Nonlinear scattering and photothermal effect measurements showed that the OL shown by one-dimensional nanostructured Na₂Ti₃O₇ can be mainly attributed to nonlinear scattering and free-carrier absorption at both irradiation wavelengths. The fabrication of one-dimensional nanostructured Na₂Ti₃O₇ with different morphologies via this simple approach paves the way for the synthesis and tuning of new one-dimensional materials with desirable photonic properties for various applications.