Intramolecular charge transfer-based linear and nonlinear optical properties of a D–π–A–π–D type organic chromophore: Experimental and computational approach

In the sight of the present demand of scientific exploration in nonlinear optics (NLO), we synthesized a symmetric donor–[Formula: see text]–acceptor–[Formula: see text]–donor (D–[Formula: see text]–A–[Formula: see text]–D) type organic chromophore [2-[2,6-di((E)-styryl)]-4H-pyran-4-ylidene]malononitrile (M1) for linear and nonlinear optical studies. The structural character of the compound M1 was confirmed using 1H NMR, [Formula: see text]C NMR, and IR spectroscopy. The intramolecular charge transfer (ICT) in molecule M1 has been analyzed using absorption and fluorescence spectrometry in different nonpolar and polar solvents. The optical bandgap, optical conductivity, and linear refractive index of M1 were also calculated using UV–Vis absorption spectrum in CHCl3. The thermogravimetric analysis (TGA) was also carried out to check the thermal stability of the compound M1 and it was found to be thermally stable up to 200∘C. Furthermore, the third-order optical nonlinearity in M1 has been investigated elaborately using the [Formula: see text]-scan technique with a continuous wave (CW) diode laser at 520[Formula: see text]nm. The nonlinear absorption ([Formula: see text]), nonlinear refraction ([Formula: see text]), and nonlinear optical susceptibility ([Formula: see text]) were computed for various solution concentrations as well as several laser powers and the magnitude of all the parameters were found to vary linearly with concentration and power. The magnitude of two-photon absorption cross-section ([Formula: see text]) was also calculated and found to be of the order of 10[Formula: see text] GM. The optical limiting performance of the compound was also studied in different solution concentrations using the same laser. Furthermore, DFT and TD-DFT theoretical calculations were performed for the support of experimental results.

Synthesis, characterization, and femtosecond third-order optical nonlinearity of Au@Ag core–shell nanoparticles

In this work, the Au@Ag bimetallic core–shell nanostructures were synthesized by a seed-mediated growth. The crystal structure, morphology, elemental composition, atomic concentration, and absorption spectrum of the as-synthesized nanoparticles were characterized by means of X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible linear absorption spectrum, respectively. The femtosecond third-order optical nonlinearities of nanoparticle dispersions were investigated by carrying out the femtosecond-pulsed [Formula: see text]-scan measurements at 800[Formula: see text]nm. The experimental results indicate that Au@Ag core–shell nanoparticles exhibit the positive refractive nonlinearity and negative absorptive nonlinearity. The third-order nonlinear refraction indexes of Au and Au@Ag nanoparticles are measured to be [Formula: see text] and [Formula: see text][Formula: see text]cm2/GW, respectively. The results show that the bimetallic nanoparticle has potential possibility in nonlinear photonic applications.

Nonlinear Absorption and Refraction of Picosecond and Femtosecond Pulses in HgTe Quantum Dot Films

We report measurements of the saturated intensities, saturable absorption, and nonlinear refraction in 70-nm thick films containing 4 nm HgTe quantum dots. We demonstrate strong nonlinear refraction and saturable absorption in the thin films using tunable picosecond and femtosecond pulses. Studies were carried out using tunable laser pulses in the range of 400–1100 nm. A significant variation of the nonlinear refraction along this spectral range was demonstrated. The maximal values of the nonlinear absorption coefficients and nonlinear refractive indices determined within the studied wavelength range were −2.4 × 10−5 cm2 W−1 (in the case of 28 ps, 700 nm probe pulses) and −3 × 10−9 cm2 W−1 (in the case of 28 ps, 400 nm probe pulses), respectively. Our studies show that HgTe quantum dots can be used in different fields e.g., as efficient emitters of high-order harmonics of ultrashort laser pulses or as laser mode-lockers.

Synthesis and Third-Order Nonlinear Synergistic Effect of ZrO2/RGO Composites

Tuning the third-order nonlinear properties of graphene by hybrid method is of great significance in nonlinear optics research. ZrO2/reduced graphene oxide (RGO) composites with different ZrO2 concentrations were prepared by a simple hydrothermal method. The morphology and structure show that ZrO2 nanoparticles were uniformly dispersed on the surface of graphene nanosheets. The nonlinear optical (NLO) characteristics of composites with different ZrO2 concentrations were studied by the Z-scan technique of 532 nm picosecond pulsed laser. The results showed that ZrO2/RGO composites had saturated absorption and positive nonlinear refraction characteristics. Meanwhile, the third-order nonlinear susceptibility of the ZrO2/RGO composite with a 4:1 mass ratio of ZrO2 to graphene oxide could reach 23.23 × 10−12 esu, which increased tenfold compared to RGO, and the nonlinear modulation depth reached 11.22%. Therefore, the NLO characteristics could be effectively adjusted by controlling the concentration of ZrO2, which lays a foundation for further research on the application of ZrO2/RGO composites in NLO devices.