Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the functi...

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation.

g-C3N4/carbon dot-based nanocomposites serve as efficacious photocatalysts for environmental purification and energy generation: A review

In this review, we survey the recent advances in nonlinear optics and the applications of two-dimensional (2D) materials. We briefly cover the key developments pertaining to research in the nonlinear optics of graphene, the quintessential 2D material. Subsequently, we discuss the linear and nonlinear optical properties of several other 2D layered materials, including transition metal chalcogenides, black phosphorus, hexagonal boron nitride, perovskites, and topological insulators, as well as the recent progress in hybrid nanostructures containing 2D materials, such as composites with dyes, plasmonic particles, 2D crystals, and silicon integrated structures. Finally, we highlight a few representative current applications of 2D materials to photonic and optoelectronic devices.

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Nonlinear optical properties and applications of 2D materials: theoretical and experimental aspects

Metal nanoparticles (MNPs) hold great technological promise because of the possibility of engineering their electronic and optical properties through material design. One of the effective methods to fabricate MNPs is ion implantation. In this review, recent results on the nonlinear optical properties of nanoparticles (including copper, silver, gold, and bismuth nanoparticles) doped in various bases have been discussed. Some specific optical nonlinear properties, such as nonlinear refraction, two-photon absorption, and optical limiting, for femtosecond, picosecond, and nanosecond laser pulses have also been covered. In addition to ion implantation, we have summarized several other methods for the preparation of composite materials, and Z-scan has been used to study the nonlinear optical properties of these materials.

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Nonlinear optical properties of metal nanoparticles: a review

Organic nonlinear optical l-phenylalanine d-mandelic acid (LPDMA) single crystals have been harvested adopting slow solvent evaporation solution growth technique (SSEST) with growth period of 15 days. The XRD studies of the crystal confirm the non-centrosymmetric nature of the crystal. The presence of functional groups for the formation of the compound was confirmed by Fourier Transform Infrared (FTIR) analysis. The UV–Visible spectral studies ascertained linear optical quality and estimation of optical parameters. The nonlinear optical property was studied from Kurtz-Perry powder technique and Z-scan technique. The quantum chemical calculations such as HOMO–LUMO and Molecular Electrostatic Potential (MEP) were calculated and presented. In order to find out various mechanical parameters such as Vicker’s hardness number (Hv), Mayer’s index (n), yield strength (σy) and stiffness constant (C11), Vicker’s microhardness tester was utilized.

Synthesis, growth, optical and third order nonlinear optical properties of l -Phenylalanine d -Mandelic acid single crystal for photonic device applications

χ(3) Measurement and optical power limiting behavior of manganese doped lithium tetraborate nanoparticles.

The organic material 3,4,5-trimethoxybenzaldehyde has been grown by slow evaporation technique using methanol as solvent. Single crystal X-ray diffraction studies shows that the grown 3,4,5-trimethoxybenzaldehyde single crystal belongs to the monoclinic system with the centrosymmetric space group P21/c. FTIR and FT-Raman spectra were recorded to identify the functional groups present in the crystal. The optical property of the grown crystal was analyzed by UV-Vis-NIR measurement. The thermal property of the grown crystal was analysed by thermogravimetric (TG) and differential thermal analyses (DTA). The dielectric studies were analyzed by using the parallel plate capacitor method. The third order nonlinear optical properties of 3,4,5-trimethoxybenzaldehyde was measured by the Z-scan technique using 532 nm diode pumped continuous wave (CW) Nd:YAG laser. The mechanical property of the grown crystal was analysed by using microhardness studies.

Growth and characterization of organic material 3,4,5-trimethoxybenzaldehyde single crystal for optical applications

A well crystallized Benzophenone single crystal was successfully grown by vertical semi transparent Bridgman technique. The lattice parameters of the grown crystal were established by single crystal x-ray diffraction technique. Fourier transform infrared spectroscopy was performed to determine the functional groups. The UV-NIR analysis revealed that the Benzophenone crystal has high transmittance in the entire visible region and the lower cutoff wavelength has been found to be 381 nm. The optical band gap energy was calculated and it is found to be 3.08 eV. The various linear optical parameters such as, Extinction coefficient (k), Refractive index (n), Reflectance, Complex dielectric constant, Optical susceptibility, Electrical conductivity and Optical polarization of the grown crystal were estimated and its variation with respect to incident photon energy was examined. Furthermore, the third order nonlinear optical properties were investigated by the z-scan technique using continuous wave Nd-YAG laser. The obtained thermophysical properties making use of photoacoustic spectroscopy show the superiority of the crystal over few other standard NLO materials.

http://iopscience.iop.org/article/10.1088/2053-1591/aa8b7b/pdf

Third harmonic generation and thermo-physical properties of benzophenone single crystal for photonic applications

Third-order nonlinearity of monoclinic and orthorhombic phase of CuNb2O6 is studied in low power regime of 532 nm by Z-scan technique. In open aperture, monoclinic CuNb2O6 possess stronger saturable absorption due to the distorted structure arising from unequal arrangement of copper atoms. Closed aperture exposes the self-defocusing nature and orthorhombic phase exhibits stronger nonlinear refraction. Variation in third-order NLO coefficient due to change in phase and morphology of CuNb2O6 confirms the influence of sintering temperature and time. Microrod monoclinic CuNb2O6 possess maximum nonlinear absorption coefficient (6.47 × 10−3 cm/W) and pure orthorhombic CuNb2O6 attains maximum nonlinear refractive index (5.13 × 10−8 cm2/W) along with higher third-order nonlinear optical susceptibility (1.91 × 10−6 esu). Higher thermal nonlinearity resulted in stronger optical limiting action with pure orthorhombic CuNb2O6 (5.16 mW, 1.26 mW) compared to other phases. For understanding the material suitability for laser safety device, nonlinearity and limiting action of CuNb2O6 thin films were demonstrated. Earlier formation of monoclinic phase with morphology change (700 °C) and transition of monoclinic rich mixed orthorhombic phase to pure orthorhombic phase (900 °C) with increase in sintering time (3–12 h) was confirmed by XRD, FTIR and SEM analysis. Thus orthorhombic CuNb2O6 material with stronger self-defocusing and optical limiting action makes it more preference than monoclinic CuNb2O6 for third-order NLO applications.

G. Vinitha

Papers

Synthesis, growth, optical and third order nonlinear optical properties of l -Phenylalanine d -Mandelic acid single crystal for photonic device applications

χ(3) Measurement and optical power limiting behavior of manganese doped lithium tetraborate nanoparticles.

Growth and characterization of organic material 3,4,5-trimethoxybenzaldehyde single crystal for optical applications

Third harmonic generation and thermo-physical properties of benzophenone single crystal for photonic applications

Third order nonlinear optical properties of monoclinic and orthorhombic CuNb2O6 under CW laser illumination