Nonresonant Third-order Optical Nonlinearities Research Articles

Femtosecond Third-Order Non-Linear Optical Properties of Unconstrained Green Fluorescence Protein Chromophores

We report herein results on the third-order non-linear optical (NLO) properties of four structurally unconstrained green fluorescence protein (GFP) chromophores, namely, 1, 2, 3, and 4. Using experimental techniques and theoretical calculations such as UV–visible spectroscopy, density functional theory (DFT), time-dependent density functional theory (TDDFT), and Z-scan techniques, we have investigated the linear absorption, ultrafast non-resonant third-order optical non-linearities, and the onset of optical-limiting thresholds of these benzylidenedimethylimidazolinone (BDI) dyes. The Z-scan measurements were performed at a wavelength of 800 nm with ∼70 femtosecond (fs) pulses. We have witnessed a strong reverse saturable absorption (fitted to three-photon absorption) for all of the molecules with fs pulse excitation. The valley–peak curves obtained from the closed-aperture Z-scan technique revealed the positive non-linear refractive index (self-focusing) nature of these molecules. We have evaluated the various third-order NLO coefficients (second hyperpolarizability, γ ∼10–33 esu), which were found to be larger than those of similar molecules reported in the recent literature.

Gamma-Ray Radiation Effect on Non-Resonant Third-Order Optical Nonlinearity of Germano-Silicate Optical Fiber

Gamma-ray radiation effect on the non-resonant third-order optical nonlinearity of the germano-silicate optical fiber has been investigated by the continuous-wave self-phase modulation method. The nonlinear refractive index, n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , of the gamma-ray irradiated optical fiber was found to increase linearly with the increase of the gamma-ray induced absorption. The increased n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has been mainly ascribed to the NBOs and Ge-realted radiation-induced defects having hyperpolarizabilities.

High non-resonant third-order optical nonlinearity of Ag–glass nanocomposite fabricated by two-step ion exchange

We observe high third-order optical nonlinearity of Ag–glass nanocomposite fabricated by a two-step ion exchange method. The nonlinear refractive index and absorption are studied using the well-known Z-scan technique. In our experiments, we use a femtosecond Ti–Sapphire laser source operating at 800nm, which is far from the plasmon resonance of the Ag nanoparticles. Our nanoparticles possess a high positive nonlinear refractive index and also a very high saturable absorption. We estimate the nonlinear refractive index to be on the order of 10−10cm2/W and the saturable absorption to be on the order of 10−5cm/W.

Near resonant and nonresonant third-order optical nonlinearities of colloidal InP/ZnS quantum dots

We have investigated the third-order optical nonlinearities of high-quality colloidal InP/ZnS core-shell quantum dots (QDs) using Z-scan technique with femtosecond pulses. The two-photon absorption cross-sections as high as 6.2 × 103 GM are observed at 800 nm (non-resonant regime) in InP/ZnS QDs with diameter of 2.8 nm, which is even larger than those of CdSe, CdS, and CdTe QDs at similar sizes. Furthermore, both of the 2.2 nm and 2.8 nm-sized InP/ZnS QDs exhibit strong saturable absorption in near resonant regime, which is attributed to large exciton Bohr radius in this material. These results strongly suggest the promising potential of InP/ZnS QDs for widespread applications, especially in two-photon excited bio-imaging and saturable absorbing.

Effect of Zn Addition on Non-Resonant Third-Order Optical Nonlinearity of the Cu-Doped Germano-Silicate Optical Glass Fiber

Cu/Zn-codoped germano-silicate optical glass fiber was manufactured by using the modified chemical vapor deposition (MCVD) process and solution doping process. To investigate the reduction effect of Zn addition on Cu metal formation in the core of the Cu/Zn-codoped germano-silicate optical glass fiber, the optical absorption property and the non-resonant third-order optical nonlinearity were measured. Absorption peaks at 435 nm and 469 nm in the Cu/Zn-codoped germano-silicate optical glass fiber were contributed to Cu metal particles and ZnO semiconductor particles, respectively. The effective non-resonant optical nonlinearity, gamma, of the Cu/Zn-codoped germano-silicate optical glass fiber was measured to be 1.5097 W(-1) x km(-1) by using the continuous-wave self-phase modulation method. The gamma of the Cu/Zn-codoped germano-silicate optical glass fiber was about four times larger than that of the reference germano-silicate optical glass fiber without any dopants. The increase of the effective non-resonant optical nonlinearity, gamma, of the Cu/Zn-codoped germano-silicate optical glass fiber, can be attributed to the enhanced nonlinear polarization due to incorporated ZnO semiconductor particles and Cu metal ions in the glass network. The Cu/Zn-codoped germano-silicate optical glass fiber showed high nonlinearity and low transmission loss at the optical communication wavelength, which makes it suitable for high-speed-high-capacity optical communication systems.

Third-order optical nonlinearities of Cu and Tb nanoparticles in SrTiO3

Some results of optical and nonlinear-optical properties of Cu and Tb nanoparticles implanted in SrTiO3 (STO) crystal are presented. The non-resonant third-order optical nonlinearities have been investigated by degenerate four wave mixing (DFWM), pump-probe and Z-scan techniques using femtosecond laser pulses.

Tellurium-enhanced nonresonant third-order optical nonlinearity in a germanosilicate optical fiber

A tellurium-doped germanosilicate optical fiber was developed by modified chemical vapor deposition and solution doping techniques. Using the continuous-wave self-phase modulation method, the nonresonant nonlinear refractive index, n2, was measured to be 5.52 x 10(-20) m2/W, which is 2 to 3 times that of the undoped germanosilicate glass fiber. Polyhedron structures TeO3 and TeO4 with GeO4 and SiO4 are believed responsible for lower phonon energy, more nonbridging oxygens, and a larger hyperpolarization, leading to the observed higher nonresonant optical nonlinearity.

Small third-order optical-nonlinearity detection free of laser parameters

We demonstrate a novel, versatile method for sensitive measurement of nonresonant third-order optical nonlinearities in waveguides. The measurement is referenced to a bulk sample with well-known nonlinear optical properties, thus ruling out the influence of laser pulse parameters like duration, contrast, and spectral phase or amplitude. Since the generated mixing product is heterodyne detected, extremely small third-order optical nonlinearities, e.g., from air-filled short waveguides, can be measured.

Pb 2+/Al 3+ codoped germano-silicate optical fiber with high non-resonant third-order nonlinearity

A germano-silicate optical fiber codoped with Pb 2+ and Al 3+ was developed by modified chemical vapor deposition and solution doping techniques. The non-resonant third-order optical nonlinearity was measured to be 6.9105 × 10 −20 m 2/W by using the continuous-wave self-phase modulation method. The enhanced non-resonant nonlinearity was ascribed to the increasing number of non-bridging oxygens due to the incorporation of the glass modifiers Pb 2+ and Al 3+, the large molar refraction from heavy metal ions Pb 2+, and the enhanced hyper-polarization from PbO doped into the core of the made fiber.

Determination of the non-resonant non-linear refractive index of germano-silicate glass fiber with an arbitrary GeO2 concentration profile

We propose a new method to measure the non-resonant third-order optical non-linearity of germano-silicate glass fiber having arbitrary GeO2 concentration profile using wavelength dependence of mode field diameter. The measured non-linear refractive indices of Samsung’s single mode fiber and the Sumitomo’s highly non-linear optical fiber were found to be in good agreement with the published results within 3.2% and 3.1% error, respectively. The method is applicable only for the optical fibers whose dispersion is dominated by the material dispersion.

Ultrafast nonresonant third-order optical nonlinearities in ZnSe for photonic switching at telecom wavelengths

We report the steady-state and time-resolved z-scan measurements of the nonresonant third-order optical nonlinearities in ZnSe at telecom wavelengths. The measurements demonstrate that ZnSe could be used for ultrafast all-optical switching at 1310 and 1550nm.

Ultrafast nonresonant third-order optical nonlinearity of fullerene-containing polyurethane films at telecommunication wavelengths

High-optical-quality polyurethane films containing a high load of (60)fullerene (C60) were prepared by reaction of the hydroxy-containing C60 and triisocyanate with the goal of obtaining enhanced nonresonant third-order optical nonlinearity. Optical nonlinearity was measured using the Z-scan technique in the wavelength range 1150–1600 nm. This revealed a positive Kerr coefficient with nonresonant n2 equal to 2.0(±0.6)×10−3 cm2/GW and excellent linear-absorption and nonlinear-absorption figures of merit at 1550 nm. The technique reported herein is a new approach to obtain fullerene films with the capacity to realize a high number density of C60 moieties. These resulted in more than 2 orders of enhancement in the third-order susceptibility over recently reported C60 sol and gel, and an enlarged second-order hyperpolarizability resulting from further enhanced charge transfer processes.

Ultrafast nonresonant third-order optical nonlinearity of a conjugated 3,3′-bipyridine derivative from 1150 to 1600 nm

A conjugated 3,3′-bipyridine derivative, an apolar structure of donor–acceptor–acceptor–donor (D–A–A–D) type was designed and characterized for third-order optical nonlinearity using Z-scan technique in the wavelength range of 1150–1600 nm. Z-scan spectra reveal a positive Kerr coefficient across this wavelength range with n2=(4.6±0.7)×10−6 cm2/GW at 1550 nm accompanied by negligible nonlinear absorption for wavelength around 1550 nm, indicating ideal figures of merit for applications in ultrafast all-optical switching.

Enhanced off-resonance optical nonlinearities of Au@CdS core-shell nanoparticles embedded in BaTiO 3 thin films

A new approach has been developed for the synthesis of Au@CdS core-shell nanoparticles (CSNs) by a directly self-assembling process. Stable Au@CdS composite colloids were prepared by thiourea, as a double functional reagents acted as the linkage agent between Cd 2+ ions and gold nanoparticles. The CdS-capped gold composite nanoparticles were successfully integrated into BaTiO 3 films. The third-order nonlinear optical properties of Au@CdS CSNs have been studied using femtosecond optical Kerr effect (OKE) technology at 800 nm. The significant enhancement of nonresonant third-order nonlinear optical nonlinearities of Au@CdS CSNs was reported for the first time.

Ultrafast third-order optical nonlinearity of polybenzonitriles

The second-order hyperpolarizabilities γ of two novel substituted polynitriles: poly( p-methyl-benzonitrile) and poly( p-hydroxylbenzonitrile) (PHBN) were measured by using femtosecond time-resolved optical Kerr effect at 820 nm. The results show that these polynitriles have large non-resonant third-order optical non-linearities. Non-resonant γ as large as 4.8×10 −32 esu has been obtained for PHBN with only eight conjugated bonds. Compared with structurally similar materials, these polynitriles have larger γ at the same conjugation length. The dependence of γ on the substitution groups and the conjugation length was also studied.

Non-resonant third-order optical non-linearity of porphyrin derivatives

Non-resonant second molecular hyperpolarisabilities (γ) of tetraphenylporphyrin (H 2 tpp) and five substituted derivatives are measured by the Z-scan technique at 784 nm; the relationship between the various structures and their corresponding molecular hyperpolarisabilities is explained on the basis of electronic interaction between the external substituents and the porphyrin core.

Nonresonant third-order optical nonlinearity of all-carbon molecules C60

The nonresonant third-order hyperpolarizability of all-carbon molecules C60 is measured by nanosecond degenerate four-wave-mixing experiment in C60 toluene solution. The value of γ1111 measured is 1.6×10−31 esu, which corresponds to an estimated value of the third-order nonlinear optical susceptibility χ(3)1111E = 3.3 × 10−9 esu for the solid compound.

Nonresonant third-order optical nonlinearity of quantum-confined CdS clusters: A third harmonic generation study

We report the first study, to the best of our knowledge, of the nonresonant third-order optical nonlinearity of quantum-confined CdS clusters using third harmonic generation from 1.91 to 0.64 μm. We observe that the nonlinearity increases with the increase in the cluster size. The intrinsic, nonresonant χ(3)CdS for ∼30, ∼15 Å thiophenolate-capped CdS clusters and [Cd10S4(SPh)16]−4 molecular clusters are 3.3×10−10, 2.5×10−11, 4.7×10−12 esu, respectively. To utilize this large nonresonant nonlinearity it is necessary to incorporate these clusters into a sample in high concentrations.