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The optical limiting properties of a 1,7-dithien-3-yl-3,5-di-4-hydroxyphenyl-azaBODIPY dye and its silver nanoparticle (AgNP) conjugate on the nanosecond timescale at 532 nm are reported. The photophysicochemical properties are compared to those of the parent 1,3,5,7-tetraphenylazaBODIPY complex. The thien-3-yl rings at the distal positions facilitate conjugation to AgNPs through the Ag-S interaction and a significant red shift of the main azaBODIPY spectral band. Favorable optical limiting properties are obtained that suggest 1,3,5,7-tetraarylazaBODIPYs and their nanoparticle conjugates merit further in-depth study in this context. This is further enhanced by conjugation to AgNPs.

The valence electronic properties of some unsubstituted and peripherally substituted oxo-titanium phthalocyanines are reported. Semiempirical quantum chemical calculations show that the nature of peripheral substituents has a strong bearing on the valence electronic properties, including the state dipole moments and absorption wavelength. The non-linear optical response was measured around the the Q-band resonance. The effect of different substituents and substitution patterns on the non-linear behaviour of the samples was determined. The combined results suggest that tuning of electronic and optical properties is effectively achieved by functionalization of the edges of the conjugated ring.

Deposition of zinc sulfide (ZnS) thin films on Si (1 0 0) and glass substrates has been performed using RF magnetron sputtering method. Film structure has been analyzed by X-ray Diffraction (XRD), while the scanning electron microscope (SEM) images have been used to explore the film morphology. FTIR and Raman spectroscopies have been used to confirm the film composition. The stoichiometry has been verified by Energy dispersive X-ray spectroscopy (EDX) technique. The XRD patterns have indicated that the films possess a polycrystalline nanocrystallite cubic structure. The optical properties of the grown films were characterized by optical transmittance measurements (UV–Vis). The deduced energy bandgaps of the films show an increase from 3.75 eV to 3.88 eV with the power source changes from 90 W to 125 W. Furthermore, Z-scan technique (CW diode laser $\lambda =635$ nm) was employed to estimate the nonlinear optical absorption of the prepared ZnS films.

The structural dependence of nonlinear optical properties associated with ADP-doped PVA/PVP polymer composites is discussed in this work. Polymer composites are fabricated using the solution casting method. X-ray diffraction (XRD) was used to perform structural analysis on these samples whose average crystallite size increases with an increase in dopant concentration. Results from UV–Vis–NIR spectra show that the samples are transparent in the IR region. The Z-scan technique was established by following the method described by Sheik-Bahae et al. The shape of the open aperture plot suggests that the samples exhibit two-photon absorption. The NLO properties such as nonlinear absorption coefficient ($\beta )$, two-photon absorption cross-section (${\sigma }_2)$ and the imaginary part of third-order nonlinear susceptibility $({\chi }^{(3)})$ were investigated at 1064 nm and these values were found to be in the order of $\sim {10}^{-7}$W/cm, $\sim {10}^{-20}$cm⁴/GW and $\sim {10}^{-14}$esu, respectively. The open aperture Z-scan method yielded optical limiting data, from which the optical limiting threshold was calculated to be in the order of $\sim {10}^{13}$W/m². Functional data analysis uses a suitable basis representation to assess the functional correlation between global and local variables.

Investigation of nonlinear absorption coefficient of eosin blue dye based side chain poly(methacrylate) films is presented using diode pumped Nd:YAG laser radiation (λ=532 nm) and the Z-scan technique. The effect of the concentration in polymer film and the increase in the number of methylene spacers, hooked to the eosin blue dye, on the nonlinear absorption coefficient is also discussed. It is shown that the nonlinear absorption coefficient in samples is due to the two-photon absorption effect. Moreover, the optical limiting characteristics of polymers film are explored.

The third-order optical nonlinear properties of CdSe quantum dots (QDs) and CdSe-C₆₀ QDs are investigated by Z-scan technique with picosecond pulses at the wavelength of 800 nm. The value of the nonlinear absorption coefficient β of CdSe-C₆₀ QDs is measured to be 2.9 cm/GW, which is about two times larger than that of CdSe QDs. The nonlinear refraction index γ of CdSe-C₆₀ QDs is -2.8 × 10^-3cm²/GW, which is about seven times larger than that of CdSe QDs. Presence of C₆₀ contributes to the larger optical nonlinearity of CdSe-C₆₀ QDs comparing with CdSe QDs.

The optical nonlinear absorption properties in sputtering Indium nitride (InN) film were investigated under the excitations of nanosecond, picosecond and femtosecond pulsed lasers by open-aperture transmission Z-scan technique (TZ-scan). Under the condition of hν > E_g, the saturable absorption (SA) phenomena induced by one-photon transition were observed in both nanosecond and picosencond pulsed TZ-scan measurements. When 2hν > E_g > hν, the film presented SA due to the two-photon transition under the excitation of picosecond laser. However, at femtosecond 800 nm, the film showed the two-photon absorption (TPA) instead of SA, and the TPA coefficient tended to a saturable value as the excitation intensity increased. The results indicate that the InN film is a kind of good saturable absorber.

3-hydroxyflavone (3-HF) is an organic molecule with excited-state intramolecular proton transfer (ESIPT) effect. The nonlinear optical properties of 3-HF in the three different polar solvents (cyclohexane, ethanol and their mixture) were investigated by Z-scan technique under the excitation of the 1064 nm picoseconds laser pulse. The 3-HFs in these solvents exhibit the self-defocusing effect and their nonlinear refraction indices are in the order of $10^{-19}{\mathrm{\text{m}}}^2/\mathrm{\text{W}}$$(10^{-12}\mathrm{\text{esu}})$. The large nonlinear refraction indices may allow them to be widely used for the optoelectronic devices.

Thioglycolic acid capped cadmium selenide (CdSe) and CdSe@ZnO core–shell quantum dots have been synthesized in aqueous phase. The sample was characterized by UV-vis spectrophotometer, TEM and Z-scan technique. The nonlinear optical parameters viz. nonlinear absorption coefficient $(\beta )$, nonlinear refractive index $(n_2)$ and third-order nonlinear susceptibilities $({\chi }^3)$ of quantum dots have been estimated using second harmonic of Nd:YAG laser. The study predicts that CdSe@ZnO quantum dots exhibits strong nonlinearity as compared to core CdSe quantum dots. The nonlinearity in quantum dots is attributed to the presence of resonant excitation and free optical processes. The presence of RSA in these nanoparticles makes them a potential material for the development of optical limiter.

Three- and four-photon nonlinear absorptions are reported by z-scan techniques in ZnS and 1% Mn²⁺ doped ZnS quantum dots (QDs) with 532 and 1064 nm radiations, respectively, obtained from a Q-switched Nd:YAG laser fundamental and its second harmonic radiation. The obtained maximum value of the 3PA coefficient in the doped ZnS QDs is ~10⁵ times that of bulk ZnS. Also, intensity-dependent saturation of 3PA has been observed and the measured experimental data are explained theoretically using a 3PA saturation model and the characteristic saturation intensity is estimated to be 0.92±0.04 GW/cm².

Nanoparticles of silver-embedded indium oxide thin films have been prepared on glass and silicon substrates. Silver concentration were 3 wt.% and 5 wt.% as measured by X-ray fluorescence. X-ray diffraction reveals that indium oxide of these samples remains amorphous even after pre-annealing at 400°C. The optical absorption of the samples manifests the surface plasmon resonance (SPR) phenomena, which varies with Ag content. The Ag nanoparticles radius was estimated with Mie classical theory by using the SPR data analysis. The nonlinear optical properties of films on glass substrate were investigated using z-scan technique. Under cw excitation the films exhibit large reverse saturation absorption and negative nonlinearities. The real and imaginary parts of third order susceptibility of the samples were measured and the imaginary part which arise from the change in absorption is found to be dominant.

Nanoparticle Lead sulfide was synthesized via simple chemical method and deposited on glass substrates at different substrate temperatures by thermal evaporation technique. The synthesized nanoparticle PbS was analyzed and confirmed by X-ray diffraction (XRD), Scanning electron microscopy SEM with EDX and thermogravimetry. The structural, optical, morphological and electrical properties of the deposited films were studied using XRD, UV-Vis, Raman, SEM with EDX, atomicforce microscopy AFM and Hall Effect measurements. The thickness of the deposited samples was measured using thickness profilometer. The Raman shift in the peak occurs toward lower energy with increasing substrate temperature deposited lead sulfide. The Z-scan study with open aperture was carried out at 532 nm using 5 ns laser pulse on the deposited films which shows that nonlinear absorption arises from saturable absorption process. The deposited PbS film exhibits p-type conductivity in Hall measurement.

Alloyed CdSe_0.3Te_0.7nanocrystals (NCs) were prepared by a thermochemical method using Thioglycolic acid (TGA) as a capping agent molecule. X-ray diffraction (XRD) and Transmission electron microscopy (TEM) analysis demonstrated hexagonal phase NCs with an average size of around 2.5 nm. Synthesized NCs indicated a narrow band emission with a peak located at 561 nm. Nonlinear optical (NLO) properties of the CdSe_0.3Te_0.7NCs have been investigated by z-scan technique using Continuum Wave He–Ne laser. The nonlinear absorption coefficient and nonlinear refraction index were obtained in the order of 10^-2 and 10^-8, respectively. The results revealed that these NCs exhibit strong NLO properties effects such as self-defocusing and two photons absorption.

Optical nonlinearity of 4-dimethyl aminopyridinium dihydrogen phosphate (DMAPDP) was studied using continuous wave of diode pumped Nd:YAG laser (532nm, 50mW). The nonlinear refractive index, nonlinear absorption coefficient and nonlinear optical (NLO) susceptibility of the sample were found to be in the order of 10${}^{-8}$cm²/W, 10${}^{-3}$cm/W and 10${}^{-6}$ esu respectively. The observed self defocusing effect was used to demonstrate the optical limiting action at 532nm. Initially, XRD analysis showed that DMAPDP crystallizes in triclinic crystal system with centrosymmetric space group $P\overline{1}$. Thermal studies explored that the material undergoes an irreversible endothermic transition at 192${}^{\circ }$C which correspond to the decomposition of material. SEM image portrays the formation of nanoparticles with grain size in the range of 45–170nm. Hence 4-dimethyl aminopyridinium dihydrogen phosphate nanoparticles can be used as potential candidate for optical limiting applications.

The nonlinear optical (NLO) properties of lanthanide bisphthalocyanine (Lu(TBPc)Pc), including first hyperpolarizability, second hyperpolarizability and reverse saturable absorption (RSA), have been investigated. Furthermore, Lu(TBPc)Pc has also been applied for optical switch based on its RSA performance.

The usage of a modified Z-scan setup for the study of optical nonlinearities of bis-phthalocyanines is discussed. The setup leads to the selection of the pure electronic nonlinear optical response purged from other possible contributions such as molecular reorientation or thermal effects. The described experimental method is based on the capability to extract the instantaneous nonlinear response of the sample, by monitoring and managing cumulative effects and taking full advantage of the large number of probing laser pulses. This kind of approach has been applied on some sandwich-type metal bis-phthalocyanines confirming its potential for an in-depth analysis of the nonlinear response of such molecules. First results on titanium, niobium and tin bis-phthalocyanines provide information on the role of the conjugation length in their nonlinear optical response.

A novel nanoscopic composite film with alternating layers consisting of anionic octacarboxylic cobalt phthalocyanine [CoPc(COONa)₈] and cationic polyethylenimine (PEI) has been fabricated by an electrostatic, layer-by-layer, self-assembly technique. UV-vis spectroscopy revealed consecutive regular deposition of CoPc(COONa)₈/PEI onto a quartz slide. The film's delicate nanostructure was characterized by atomic force microscopy and small angle X-ray diffraction. Third-order nonlinear properties of the film performed using Z-scan measurements with 21 ps laser pulses at the incidence wavelength of 532 nm showed rather strong, nonlinear reverse saturable absorption.

Novel heteropentameric porphyrins-pyrene arrays, in which four meso-tetraphenyl porphyrins are linked to the center unit of pyrene by four acetylenyl bonds, were designed and synthesized. The newly synthesized heteropentameric compounds have been characterized by a wide range of spectroscopic methods. The third-order nonlinear optical (NLO) properties of both the metal-free and zinc compounds of the three-dimensional arrays were investigated by Z-scan experiments, showing enhanced NLO properties compared with that of the porphyrin and pyrene monomers.

Films with alternating layers containing anionic tetracarboxylic copper phthalocyanine [CuPc(COONa)₄] and cationic polydiallydimethylammonium chloride (PDDA) were fabricated by electrostatic self-assembled layer-by-layer (LBL) technique. The delicate structure of the film was characterized by a series of techniques. The third-order nonlinear optical properties of the film were measured by the Z-scan technique with laser duration of 4 ns and 21 ps at the wavelength of 532 nm. The film exhibited excellent nonlinear absorption and self-focusing effect. The second-order molecular hyperpolarizability γ value of the film was much larger than that of CuPc(COONa)₄ aqueous solution under the irradiation of whether ns or ps pulses. A series of damage experiments of the film for the intense laser pulses were conducted to prove the reliability of the experimental results under the conditions.

Two major reasons limit porphyrins photonic applications: (i) the difficulty of handling them in liquid solutions and (ii) their degradation with long exposure to light. This necessitates the use of appropriate solid matrices to host the porphyrin compounds such as Nafion (117), a stable and inert ion exchange polymer. The first part of this publication confirms such a possibility. In addition to their effective NLO properties, an enhancement of the Soret and Q-bands' absorbance width have been observed by blending three different porphyrin molecules in the Nafion column matrix membrane. This is an important development towards achieving efficient photon-harvesting medium for possible application in photonic devices. The second part of this contribution reports on the self-assembly/molecular recognition of a specific class of porphyrins giving rise to tubular nano-systems with potential THG nonlinear properties.