Large Third-order Optical Nonlinearity Research Articles

Preparation and nonlinear optical properties of indium nanocrystals in sodium borosilicate glass by the sol–gel route

The sodium borosilicate glass doped with indium nanocrystals have been successfully prepared by sol–gel route. The thermal stability behavior of the stiff gel is investigated by thermogravimetric (TG) and differential thermal (DTA) analysis. The crystal structure of the glass is characterized by X-ray powder diffraction (XRD). Particle composition is determined by X-ray photoelectron spectroscopy (XPS). Size and distribution of the nanocrystals are characterized by transmission electron microscopy (TEM) as well as high-resolution transmission electron microscopy (HRTEM). Results show that the indium nanocrystals in tetragonal crystal structure have formed in glass, and the average diameter is about 30nm. Further, the glass is measured by Z-scan technique to investigate the nonlinear optical (NLO) properties. The third-order NLO coefficient χ(3) of the glass is determined to be 2.81×10−10esu. The glass with large third-order NLO coefficient is promising materials for applications in optical devices.

Molecular modeling of two-photon absorption and third-order nonlinearities of polymethine dyes for all-optical switching

Stimulated by a recent experimental report [Hales JM et al. (2010) Science 327:1485-1488], two-photon absorption and third-order optical nonlinearities of selenopyrylium- and bis(dioxaborine)-terminated polymethine dyes (called SE-7C and DOB-9C) used for all-optical switching were investigated theoretically with time-dependent DFT (TD-DFT) and response theory as well as visualized real-space analysis. The calculated results for the first hyperpolarizability and second hyperpolarizability demonstrated that the two molecules both have large third-order optical nonlinearities. Using real-space analysis, we were able to visually determine that in the one-photon absorption (OPA) process, the first singlet excited state of SE-7C and DOB-9C is an intramolecular charge transfer (ICT) excited state with strong absorption, while the second excited state of these dyes (also termed the "ICT state") shows weak absorption. However, in the two-photon absorption (TPA) process, a larger TPA absorption cross-section was predicted for the second excited state. In this paper, we describe the properties of the S2 excited state, incorporating charge transfer and the transition moment, via real-space analysis, which was very important for understanding the TPA characteristics of the S(2) state.

Large third-order optical nonlinearity of Mg-doped PbS/PVA freestanding nanocomposite films

Mg-doped PbS/PVA freestanding nanocomposite films were successfully prepared by a simple chemical route. X-ray diffraction patterns confirm the formation of all the films with cubic phase of PbS. Optical absorption spectra showed the blue shifted phenomena and the band gaps of Mg : PbS/PVA films increase with an increase in Mg concentration. The increase in resistivity with reducing particle size was examined for these films. The Z-scan results showed that the freestanding nanocomposite films exhibit the large nonlinear refractive index and absorption coefficients with negative sign and they are increased with Mg doping. Third-order nonlinear optical susceptibility and figure of merit were calculated and the maximum value is found to be about 3.405 × 10−5 esu and 2.067 × 10−9 esu m, respectively, for higher Mg-doped film which is three orders of magnitude larger than that observed in the substrate-supported films as reported earlier in the literature. The results show that the Mg : PbS/PVA films have great potential applications in future optical devices.

Universal Preparation of Novel Metal and Semiconductor Nanoparticle–Glass Composites with Excellent Nonlinear Optical Properties

We report on a simple and universal method for fabricating various kinds of metal and semiconductor (Si, Ge, Bi, and Cu) nanoparticle–glass composites by using metallic Al as a reducing agent in the raw materials of the glass batches. By taking advantage of the redox equilibrium that sets up between the Al reducing agent and various oxides, crystal nuclei such as Si and Ge atom clusters are already formed during the melt-quenching stage. During the subsequent heat-treatment stage, the nanoparticles grow on the nuclei by a process of diffusion. The nanoparticle size can be controlled by heat-treatment temperature and holding time. The fabricated nanoparticle–glass composites exhibit large third-order optical nonlinearities (χ3 up to 10–8 esu) and an ultrafast response time (within picoseconds), which makes them possible to manufacture ultrafast all-optical switches.

Nonlinear optical properties of lead nanocrystals embedding glass induced by thermal treatment and femtosecond laser irradiation

We fabricated lead nanocrystals inside a specially designed borosilicate glass by two parallel approaches, thermal stimulation and femtosecond laser irradiation. Thermal treatment can precipitate lead nanocrystals inside whole glass, while femtosecond laser irradiation can induce lead nanocrystals within selective area of glass. The fabricated nanocomposite exhibits large third-order optical nonlinearity and ultrafast response time, which is suitable for fabrication of ultrafast optical switches. Furthermore, the femtosecond laser induced refractive index difference between lead crystalline and glass is about 0.13, which is enough to fabricate optical devices such as photonic crystals.

Four-wave mixing in InGaAs/AlAsSb intersubband transition optical waveguides

Four-wave mixing (FWM) in an InxGa1-xAs/AlAsySb1-y intersubband transition (ISBT) optical waveguide operating in the 1.55-μm wavelength region is discussed. The third-order optical nonlinear susceptibilities of InxGa1-xAs/AlAsySb1-y multiple quantum wells (MQWs) are estimated theoretically. ISBT excitation causes large third-order optical nonlinearity. χ(3) values of more than 1 × 1016 m2/V2 are obtained. The propagation of interacting waves for FWM in InxGa1-xAs/AlAsySb1-y ISBT optical waveguides is discussed. The interaction length is limited not only by phase matching but also by ISBT absorption. Sufficiently high FWM conversion efficiencies were obtained theoretically and experimentally for realizing coherent wavelength convertors. FWM in an InxGa1-xAs/AlAsySb1-y ISBT waveguide is a promising method for realizing compact and high-efficiency coherent wavelength conversion.

Fabrication and third-order optical nonlinearities of Na 2O–B 2O 3–SiO 2 glasses containing metallic Bi, Bi 2O 3 and Bi 2S 3 crystals

We report a facile method to realize the fabrication of Na 2O–B 2O 3–SiO 2 glass containing metallic Bi, Bi 2O 3 and Bi 2S 3 crystals. The microstructures of the glasses are investigated in detail by means of XRD, XPS, and TEM techniques. Furthermore, the third-order optical nonlinearities of the glasses are measured using femtosecond Z-scan technique at the wavelength of 800 nm with a pulse width 200 fs. Results show that the glasses exhibit the large third-order optical nonlinearities, and the third-order optical nonlinear susceptibility χ (3) of Na 2O–B 2O 3–SiO 2 glass containing metallic Bi, Bi 2O 3 and Bi 2S 3 crystals are determined to be 5.81 × 10 −11 esu, 6.01 × 10 −11 esu, and 8.71 × 10 −10 esu, respectively. In particular, the third-order optical nonlinear absorption of the glasses are excellent, which have potential applications in the lasers as Q-switching elements and optical limiters.

Large third-order optical nonlinearity of silver colloids in silica glasses synthesized by ion implantation

Silver ion implantations in fused silica glasses have been made to synthesize silver nanocluster–glass composites and a combination of ‘Anti-Resonant Interferometric Nonlinear Spectroscopy (ARINS)’ and ‘Z-scan’ techniques has been employed for the measurement of the third-order optical susceptibility of these nanocomposites. The ARINS technique utilizes the dressing of two unequal-intensity counter-propagating pulsed optical beams with differential nonlinear phases, which occurs upon traversing the sample. This difference in phase manifests itself in the intensity-dependent transmission, measurement of which enables us to extract the values of nonlinear refractive index ( η 2) and nonlinear absorption coefficient ( β), finally yielding the real and imaginary parts of the third-order dielectric susceptibility ( χ (3)). The real and imaginary parts of χ (3) are obtained in the orders of 10 −10 e.s.u for silver nanocluster–glass composites. The present value of χ (3), to our knowledge, is extremely accurate and much more reliable compared to the values previously obtained by other workers for similar silver-glass nanocomposites using only Z-scan technique. Optical nonlinearity has been explained to be due to two-photon absorption in the present nanocomposite glasses and is essentially of electronic origin.

Large Third-Order Optical Nonlinearity in Directly Synthesized Single-Walled Carbon Nanotube Films

Large third-order optical nonlinearity is observed in single-walled carbon nanotube (SWNT) films that are directly synthesized by CVD method rather than post-deposited from solution. Through z-scan method, the third-order nonlinear susceptibility (chi(3)) is measured, and the |Im chi(3)| is 1.8 x 10(-7) esu at 1064 nm, which is among the highest reported values for optical nonlinear materials. Combined with their transparent morphology and ultrafast carrier relaxation time, our results indicate the promising prospect of directly synthesized SWNT films as saturable absorbers using in mode-lock lasers or ultrafast switching materials in optical telecommunications.

Stimulated supercontinuum–radiation generation of carbon disulfide by all-trans-β-carotene fluorescence enhancement effect in liquid core optical fibre

We demonstrate stimulated supercontinuum-radiation of carbon disulfide (CS2) influenced by biological molecules all-trans-β-carotene in liquid core optical fibre (LCOF). By virtue of the broad fluorescence characteristics and large third-order optical nonlinearities of all-trans-β-carotene, the high-order Stokes lines of stimulated Raman scattering (SRS) and the multi-order Stokes lines of stimulated Brillouin scattering (SBS) excitated by SRS are observed at low input-laser energies. The results indicate that the fluorescence not only enhances the SRS, but also the SBS. These Stokes lines generate the SRS-SBS supercontinuum radiation (RBSR). A flat-amplitude bandwidth of 110 nm from 515 nm to 625 nm is observed when a frequency-doubled Nd:YAG laser at 532 nm with an energy of 0.86 mJ is used. This result is expected to be useful for the multi-wavelength fibre laser.

Facile synthesis and large third-order optical nonlinearity of Manganese-loaded mesoporous silica thin films

An in - situ reduction method is adopted to incorporate MnO 2 nanoparticles into mesochannels of silica thin films by using KMnO 4 as the oxidizing agent and manganese precursor. As the reduction time in KMnO 4 solution increases, the ordered mesostructure collapses, and the loaded MnO 2 nanoparticles become bigger in size, resulting in a narrower band gap. Z scan measurement demonstrates a large third-order nonlinear susceptibility of the composite films under the picosecond Nd:YAG laser excitation. A sign reversion of the third-order nonlinear refractive index coefficient in the sample with longer reduction time is also observed, which can be attributed to the variation in the band gap energy.

Design of Polymethine Dyes with Large Third-Order Optical Nonlinearities and Loss Figures of Merit

All-optical switching applications require materials with large third-order nonlinearities and low nonlinear optical losses. We present a design approach that involves enhancing the real part of the third-order polarizability (gamma) of cyanine-like molecules through incorporation of polarizable chalcogen atoms into terminal groups, while controlling the molecular length to obtain favorable one- and two-photon absorption resonances that lead to suitably low optical loss and appreciable dispersion enhancement of the real part of gamma. We implemented this strategy in a soluble bis(selenopyrylium) heptamethine dye that exhibits a real part of gamma that is exceptionally large throughout the wavelength range used for telecommunications, and an imaginary part of gamma, a measure of nonlinear loss, that is smaller by two orders of magnitude. This combination is critical in enabling low-power, high-contrast optical switching.

Large Third-Order Optical Nonlinearity of Cadmium Sulphide Nanoparticles Embedded in Polymer Thin Films

A simple method for synthesis of well dispersed cadmium sulphide nanoparticles embedded in a polyethylene glycol matrix (PEG 400) in thin film form is presented. The large blue shift of the band gap energy of the CdS nanoparticles compared to the bulk semiconductors is observed via UV-vis absorption spectra. Photoluminescence spectra of CdS nanocomposite films show that the emission peaks shift towards the longer wavelength with the increase of annealing temperature. Transmission electron microscopic images as well as Raman scattering studies confirm the CdS nanometer size particle formation within the polymer matrix. The particle size is about 8 nm. Selected area electron diffraction (SAED) shows the cubic zinc blende polycrystalline rings. Third-order optical nonlinearity of the CdS nanoparticles embedded in polymer thin films is studied with the Z-scan technique under 1064 nm excitation. The results show that the CdS nanocomposite film exhibits negative nonlinear refraction index and positive absorption coefficient. The film shows large optical nonlinearity, and the magnitude of the third-order nonlinear susceptibility of the film is calculated to be 1.73 × 10−9 esu. The corresponding mechanism is discussed.

Syntheses, crystal structures, third-order nonlinear optical properties and thermal properties of two infinite (6, 3) net complexes

Two new complexes {[Co(bbbm) 1.5(NO 3) 2]·H 2O} n ( 1) and [Cd(bbbm) 1.5(NO 3) 2] n ( 2) (bbbm = 1,1’-(1,4-butanediyl)bis-1H-benzimidazole) have been synthesized and structurally characterized. Both complexes are built up by two-dimensional coordination networks with (6, 3) nets. The third-order nonlinear optical (NLO) properties of the two complexes are determined and the results show that they not only possess large third-order NLO absorptive effects, but also display strong refractive behaviors. The hyperpolarizability | γ| values are 2.2 × 10 −29 esu for complex 1, and 1.6 × 10 −30 esu for complex 2. The NLO effective of complex 1 is stronger than that of 2 due to the decreased π back-donation capacity from Co(II) to Cd(II). Thermal analysis studies show that complex 1 is less stable and begins to decompose at 131 °C. While complex 2 is stable up to 257 °C.

Large third-order optical nonlinearities in brilliant green solutions induced by CW He-Ne laser

Laser induced third-order nonlinear optical responses of Brilliant Green solution (which belongs to triphenylmethane organic dye group) was investigated by utilizing single beam Z-scan technique using a continuous wave He-Ne laser at the wavelength of 632.8 nm. It was observed that the material exhibits self-defocusing and saturation absorption type optical nonlinearity behavior. The measurements of the real and imaginary parts of the third-order nonlinear optical susceptibility were carried out at several incident laser irradiations and different dye concentrations. It was found that the increase in any of the incident laser intensity or solution concentration leads to the linear increase of the nonlinear refractive index. The obtained values of the third-order nonlinearities of Brilliant Green solutions are amongst the highest reported CW regimes, to the best of our knowledge. This study shows a great potential of the Brilliant Green for the application in nonlinear optical devices.

Influence of amplified spontaneous emission and fluorescence of β-carotene on stimulated Raman scattering of carbon disulfide

β-carotene with double fluorescence characteristics and large third-order optical nonlinearities, which is dissolved in the carbon disulfide (CS2) as the core medium of a liquid core optical fiber (LCOF), is applied in the study of the CS2 stimulated Raman scattering (SRS). The results of this study show that when the concentrations of solution are more than 3.72×10−7 mol/L, the amplified spontaneous emission (ASE) of β-carotene is the main factor influencing the threshold and intensity of Stokes lines; when the concentrations of solution are lower than 3.72×10−7 mol/L, the ASE disappears and the fluorescence plays the key role: The high-order Stokes lines may be observed at very low input-laser power, and the Stokes thresholds decrease as the solution concentration increases. The result may be widely used in the study of broadband stimulated radiation laser and seeding laser.

Determination of large third-order optical nonlinearities in tetra-tert-butylphthalocyaninatogallium iodide film

Using the Z-scan technique with 532 nm 4 ns laser pulses at various energy levels and repetition rates, we investigated the optical nonlinearities of tetra-tert-butylphthalocyaninatogallium iodide (t-Bu)4PcGaI. As a result, we found that the soluble peripherally tert-butyl-substituted phthalocyanine bound with the core of gallium iodide exhibited a giant two-photon absorption coefficient and Kerr refractive index. This suggests the potential applications of this material in numerous fields of nonlinear optics. However, when tackling the large nonlinearly induced loss and phase distortion analytically, we failed to fit the corresponding experimental results with the existent series sum formulas, which retain only the first few terms in the expansion. We performed the fitting by retrieving the high-order terms and justified this approach by dealing with the light-matter interaction and wave propagation.

Fe/SrBi2Nb2O9 composite thin films with large third-order optical nonlinearities

Fe/SrBi 2 Nb 2 O 9 composite thin films have been fabricated on fused quartz substrates at room temperature by RF magnetron sputtering technique. XRD result demonstrated that the Fe and SrBi 2 Nb 2 O 9 (SBN) were well crystallized. Atomic force microscope (AFM) analysis indicated that the composite films have less rough surface. Their chemical composition was characterized by X-ray fluorescence spectrometer. The optical absorption of the films were measured from 300 nm to 800 nm, and the absorption peak was observed near 500 nm due to the surface plasma resonance of Fe particles. The nonlinear optical properties of Fe/SBN thin films were determined using z-scan method at a laser wavelength of 532 nm with laser duration of 25 ps, closed to the resonance frequency. z-Scan results show that Fe/SBN composite films exhibit a great picosecond nonlinear optical response, and the real and imaginary parts of the third-order nonlinear susceptibility ( χ (3) ) at a Fe concentration of about 15% were 6.73 × 10 −7 esu and −1.02 × 10 −7 esu, respectively.

Large third-order optical nonlinearity realized in symmetric nonpolar carotenoids

We show that a very large enhancement of third-order optical nonlinearity $(\ensuremath{\gamma})$ of $\ensuremath{\pi}$-conjugated molecules can be realized without a major redshift of the absorption spectrum that disturbs optical transparency in the visible region. By changing the number $(n)$ of C=C bonds of $\ensuremath{\beta}$ carotene $(n=11)$ from 7 to 15, a remarkable 3.4-fold increase in the $\ensuremath{\gamma}$ value was observed when $n=15$ relative to that of $\ensuremath{\beta}$ carotene. This enhancement of $\ensuremath{\gamma}$ mainly originates from three-photon resonance of a lowest optically allowed excited state. The controversial higher-lying essential state is not important for generating the large value of $\ensuremath{\gamma}$.

Large Third-Order Optical Nonlinearity of a Novel Copper Phthalocyanine–Ferrocene Dyad

Third-order optical nonlinearity of a novel copper phthalocyanine-ferrocene dyad is measured by femtosecond forward degenerate four-wave mixing (DFWM) technique at 800 nm. The second-order hyperpolarizability of the novel copper phthalocyanine–ferrocene dyad is measured to be 1.74 × 10-30 esu. This large and ultrafast third-order optical nonlinear response is mainly enhanced by the formation of intramolecular charge-transfer which can enhance the delocalized movements of the large π-electrons in the molecules.