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Tailoring the nonlinear optical properties of materials through extrinsic parameter controls is advantageous for many applications. In this article, ultrafast laser pulse repetition rate induced switching of reverse saturable absorption to saturable absorption of water is reported. For the investigations, a conventional open aperture z-scan measurement system equipped with a variable repetition rate ultrafast laser source operating at the wavelength of 1030 nm was employed. A combination of weak saturable absorption and strong reverse saturable absorption induced by three-photon absorption is observed at low and moderate repetition rates. At repetition rates above 5 kHz, there is a significant variation in nonlinear absorption, where the reverse saturable absorption starts to diminish and saturable absorption increases. For repetition rates beyond 100 kHz, the nonlinearity gets reversed, where water tends to behave more like a saturable absorber with a weak three-photon absorption component. • Investigation of ultrafast nonlinear optical absorption of de-ionized water. • Ultrafast laser pulse repetition rate affects the nonlinearity in water. • The nonlinear absorption is tunable by varying the laser pulse repetition rate. • Switchover from reverse saturable absorption to saturable absorption reported. [ABSTRACT FROM AUTHOR]

Nonlinear optical properties of multicomponent tellurite glasses doped with Er 3+ ions were investigated by open aperture Z-scan measurements. Compositional and linear optical properties of the glasses were examined by the energy dispersive X-ray spectrum and UV–vis–NIR absorption spectrum analysis respectively. The mechanism behind the optical nonlinearity and optical limiting efficiency was successfully explained by evaluating the physical properties such as density, refractive index and polarizability of the glasses. The nonlinear properties critically depend on the polarizability, which is found to increase with the addition of Er 3+ ions by the creation of non-bridging oxygen ions. By the systematic addition of Er 3+ ions, we have dictated the physical properties and thus tuned the optical limiting efficiency of the glasses. This makes the Er 3+ -doped multicomponent tellurite glasses flexible tunable optical limiters for potential device applications. [ABSTRACT FROM AUTHOR]

Wavelength dispersion of optical power limiting is an important factor to be considered while designing potential optical limiters for laser safety applications. We report the observation of broadband, ultrafast optical limiting in reduced graphene oxide (rGO), measured by a single open aperture Z-scan using a white light continuum (WLC) source. WLC Z-scan is fast when the nonlinearity is to be measured over broad wavelength ranges, and it obviates the need for an ultrafast tunable laser making it cost-economic compared to conventional Z-scan. The nonlinearity arises from nondegenerate two-photon absorption, owing mostly to the crystallinity and extended p conjugation of rGO. [ABSTRACT FROM AUTHOR]

We report on enhanced nonlinear optical absorption and optical limiting in β-MnO 2 sponge-like nanowire network decorated with Ag nanoparticles excited by nanosecond laser. A simple two-step process is used to prepare the samples. The structure, morphology and the elemental analysis of the prepared samples are studied using x-ray diffraction, field emission scanning electron microscopy and energy-dispersive x-ray spectroscopy. Nonlinear optical absorption properties of the samples in solution is studied using the open aperture Z-scan technique employing 5 ns laser pulses at 532 nm. Nonlinear transmission measurements show that β-MnO 2 exhibit weak saturable absorption at low fluence and large optical limiting at high fluence, while upon decoration with Ag particles, Ag/β-MnO 2 shows strong saturable absorption at low fluence and enhanced optical limiting at higher fluence with an optical limiting threshold value three times lower than that of bare β-MnO 2 nanowires. The results indicate that these materials are potentially useful for constructing saturable absorbers and optical limiters. • β-MnO 2 nanowire network decorated with Ag nanoparticles. • Simple and cheap doped nanowire synthesis process. • Ag-doped β-MnO 2 nanowires may lead to cheap and efficient optical limiters. [ABSTRACT FROM AUTHOR]

Hetero atom doped graphene - metal nanoparticle hybrids have received increasing attention owing to their unique electronic properties, large specific surface area, very high conductivity and more electronic interactions. Herein, we report for the first time a hydrothermal assisted strategy for developing novel class of nitrogen (N) and sulfur (S) co-doped graphene/Ag nano morphotypes (sphere, cube and wire) hybrids for enhanced optical limiting (OL) and surface-enhanced Raman scattering (SERS) applications. Two probe molecules, Rhodamine 6G and para-aminothiophenol, are chosen to determine the enhancement performance of the as-prepared SERS-active substrate. Our results signified that the Ag nanocube-N, S codoped graphene hybrid based SERS-active substrate presents excellent performances for sensing R6G with an enhancement factor of 1.07 × 10 7 . Further, this SERS substrate reveals outstanding capability to detect P -ATP molecules with detection limit of approximately 1.0 × 10 −12  M. Moreover, the non-linear optical absorption studies results show that the OL properties were appreciably enhanced after the insertion of Ag nanostructures on the NSG surface. Thus, OL properties of the two-dimensional N, S-codoped graphene can be effectively modified by absorbing AgNPs of different morphology on its surface. All of the results signify that these hybrid structures will show extended applications for SERS sensing and optoelectronic fields. [ABSTRACT FROM AUTHOR]