Z-scan and optical limiting properties of Hibiscus Sabdariffa dye

The intensity-dependent refractive index n ₂ and the nonlinear susceptibility χ ⁽³⁾ of Hibiscus Sabdariffa dye solutions in the nanosecond regime at 532 nm are reported. More presicely, the variation of n ₂, β, and real and imaginary parts of χ ⁽³⁾ versus the natural dye extract concentration has been carried out by z-scan and optical limiting techniques. The third-order nonlinearity of the Hibiscus Sabdariffa dye solutions was found to be dominated by nonlinear refraction, which leads to strong optical limiting of laser.     

CdSe量子点的线性和非线性光学特性

主要从实验和理论两个方面,探讨了强受限尺寸区域内不同尺寸对CdSe量子点线性和非线性光学性质的影响.用吸收光谱研究了量子点尺寸与吸收峰之间的关系,用皮秒Z扫描技术研究了共振和非共振情况下(激发光波长分别为532和1064nm),尺寸与三阶非线性极化率之间的关系.基于电子能量状态理论和局域场增强理论对量子点进行分析,得到了CdSe不同尺寸的三阶非线性效应,研究了尺寸对量子点非线性光学性质的影响.结果表明,由激发态粒子数布局改变和纳米颗粒增大引起的非线性共振增强效应相当,二者共同作用使得三阶极化率增强20倍左右,且用532nm的共振频率激发4.3nm CdSe量子点时,χ⁽³⁾具有最大值2.0×10^-11esu. 关键词： CdSe量子点 三阶非线性 Z扫描')" href="#">Z扫描 量子限域效应     

Nonlinear refraction in nanocrystalline silicon carbide films

Nonlinear refraction in nanocrystalline SiC films, which have been obtained using the method of direct deposition of carbon and silicon ions with an energy of 100 eV at substrate temperatures from 900 to 1150°C, has been investigated. It has been shown that the films exhibit a large third-order nonlinear susceptibility χ ⁽³⁾ ～ 10^?6 esu (at λ = 1064 nm and τ _p = 10 ns).     

Thermally induced nonlinear optical response and optical power limiting of acid blue 40 dye

We report the investigations of thermally induced third-order nonlinear optical and optical limiting characterizations for various concentrations of acid blue 40 dye in N,N-Dimethyl Formamide, studied by employing z-scan technique under cw He–Ne laser irradiation at 633 nm wavelength. The samples exhibited nonlinear absorption and nonlinear refraction under the experimental conditions. For lower concentration, the samples display both saturable absorption (SA) and reverse saturable absorption (RSA); whereas with increase in concentration, RSA behaviour prevails. The estimated values of the effective coefficients of nonlinear absorption β_eff, nonlinear refraction n₂ and third-order nonlinear susceptibility χ⁽³⁾ were found to be of the order of 10^?2 cm/W, 10^?4 esu and 10^?6 esu respectively. Multiple diffraction rings were observed when the samples were exposed to laser beam due to refractive index change and thermal lensing. The effect of concentration and the laser intensity on the self-diffraction ring patterns was studied experimentally. The acid blue 40 dye also exhibited strong optical limiting properties under cw excitation and reverse saturable absorption is found to be the dominant nonlinear optical process leading to the observed nonlinear behaviour.     

三-α-(2,4-二甲基-3-戊氧基)溴硼亚酞菁的三阶非线性光学性质研究

应用Z扫描技术，在波长为532nm、脉宽为8ns条件下，对一种新型亚酞菁配合物三-α-(2,4-二甲基-3-戊氧基)溴硼亚酞菁的三阶非线性光学特性进行了研究，结果发现，该新化合物有较强的反饱和吸收(β=3.7×10^-10 m/W)效应和非线性自聚焦折射效应(n₂=7.2×10^-11esu)，其三阶非线性极化率χ⁽³⁾=1.1×10^-11esu.分析了溴硼亚酞菁配合物特殊的锥形分子结构和重原子溴的轴向配位等因素对其三阶非线性光学性质的重要影响. 关键词： 亚酞菁 Z扫描 三阶光学非线性     

Nonlinear optical response of silver and copper nanoparticles in the near-ultraviolet spectral range

The nonlinear optical response of silver and copper nanoparticles synthesized by ion implantation in silica glasses is studied in the near-ultraviolet spectral range at a wavelength of 354.7 nm. The real and imaginary parts of the third-order nonlinear susceptibility χ⁽³⁾ of composite materials are measured. It is shown that the quantity Imχ⁽³⁾ is due to saturated absorption, while Reχ⁽³⁾ is due to the self-defocusing effect in composite materials.     

Theoretical and experimental studies on laser-induced transient gratings in laser dyes

Laser-induced transient grating technique has been used to measure the diffraction efficiency (η) and calculate the third-order nonlinear susceptibility (χ⁽³⁾) of some laser dyes. Theoretical simulations have been carried out on η and χ⁽³⁾ as a function of wavelength covering the spectral range corresponding to the first excited singlet state of the dyes. Theoretically simulated values have been found in agreement to those observed experimentally. The decay profiles for these dyes have been measured by using diffraction of a delayed probe laser pulse to estimate the relaxation times in the excited state.     

Nonlinear optical properties of Cu nanoclusters by ion implantation in silicate glass

Metal nanocluster composite glass prepared by 180 keV Cu ions into silica with dose of 1 × 10¹⁷ ions/cm² has been studied. The microstructural properties of the nanoclusters were analysed by optical absorption spectra and transmission electron microscopy (TEM). Third-order nonlinear optical properties of the nanoclusters were measured at 1064 nm and 532 nm excitations using Z-scan technique. The nonlinear refraction index, nonlinear absorption coefficient, and the real and imaginary parts of the third-order nonlinear susceptibility were deduced. The mechanisms responsible for the nonlinear response were discussed. Absolute third-order nonlinear susceptibility χ⁽³⁾ of this kind of sample was determined to be 2.1 × 10⁻⁷ esu at 532 nm and 1.2 × 10⁻⁷ esu at 1064 nm, respectively.     

Ag:Bi2O3复合膜的线性和非线性光学性质

从实验和理论两个方面，探讨了金属Ag不同掺杂浓度对Ag:Bi₂O₃复合膜线性和非线性光学性质的影响. 用吸收光谱研究了Ag浓度与Ag:Bi₂O₃复合膜表面等离子体共振带之间的关系；用皮秒Z-扫描技术研究了共振和非共振情况下(激发光波长分别为532nm和1064nm)，金属Ag浓度与复合膜三阶非线性极化率的关系. 基于表面等离子体共振理论和局域场增强理论对复合膜进行了分析，得到了不同Ag浓度时Ag:Bi₂O₃复合膜的三阶非线性效应，研究了激发波长和金属浓度对复合膜线性和非线性光学性质的影响. 结果表明，等离子体共振增强和合适的金属掺杂浓度使得三阶极化率增强二个量级，在Ag浓度为35％左右和接近等离子体共振频率(相应吸收带位于560nm—622nm)的532nm激发时，χ⁽³⁾具有最大值2.4×10^-9esu. 关键词： 金属纳米颗粒 复合膜 三阶非线性 表面等离子体共振     

Enhanced nonlinear optical responses in metal-glass nanocomposites

The “engineered” nonlinear nanocomposite materials with extremely large values of optical Kerr susceptibility and fast temporal responses that can be precisely tuned to satisfy the requirements of switching applications is of current interest in photonics. Metal quantum-dot composite glasses can exhibit enhanced optical susceptibility, χ⁽³⁾, whose real and imaginary parts are related to the intensity-dependent refractive index and two-photon absorption coefficient, respectively. Classical (dielectric) and quantum confinement effects come into play in the nonlinear optical responses of these nanocomposites. Metal nanocluster-glass composites have been synthesized by 200 keV Cu⁺ and 1.5 MeV Au⁺ ion implantations in fused silica glasses at a dose of 3 × 10¹⁶ ions/cm², followed by thermal annealing in reducing atmosphere to promote cluster growth. UV-Visible spectroscopy has revealed prominent linear absorption bands at characteristic surface plasmon resonance (SPR) frequencies signifying appreciable formation of copper and gold colloids in glass matrices. Third-order optical properties of the composite materials have been studied by Z-Scan and Anti-Resonant Interferometric Nonlinear Spectroscopy (ARINS) measurements. The sign of nonlinear refraction is readily obtained from the Z-Scan signatures. The ARINS technique utilizes the dressing of two unequal-intensity counter-propagating pulsed light beams with differential nonlinear phases, which occur upon traversing the sample if it exhibits nonlinear optical response. This difference in phase manifests itself in the intensity-dependent transmission. The nonlinear refractive index, nonlinear absorption coefficient, the real and imaginary parts of the third-order optical susceptibility have been extracted.     

Analytical study of four-wave mixing with large atomic coherence

Four-wave mixing in resonant atomic vapors based on maximum coherence induced by Stark-chirped rapid adiabatic passage (SCRAP) is investigated theoretically. We show the advantages of a coupling scheme involving maximum coherence and demonstrate how a large atomic coherence between a ground and an highly excited state can be prepared by SCRAP. Full analytic solutions of the field propagation problem taking into account pump field depletion are derived. The solutions are obtained with the help of an Hamiltonian approach which in the adiabatic limit permits to reduce the full set of Maxwell-Bloch equations to simple canonical equations of Hamiltonian mechanics for the field variables. It is found that the conversion efficiency reached is largely enhanced if the phase mismatch induced by linear refraction is compensated. A detailed analysis of the phase matching conditions shows, however, that the phase mismatch contribution from the Kerr effect cannot be compensated simultaneously with linear refraction contribution. Therefore, the conversion efficiency in a coupling scheme involving maximum coherence prepared by SCRAP is high, but not equal to unity. Received 16 August 2002 Published online 4 February 2003 RID="a" ID="a"e-mail: korsunsky@physik.uni-kl.de     

Third-order optical nonlinearities of α,ω-dithienylpolyenes and oligo(thienylvinylene)

α,ω-Dithienylpolyenes and oligo(thienylvinylene) are interesting third-order nonlinear optical materials for a variety of device applications. To better understand the third-order nonlinear response of these materials, the third-order susceptibilities (χ⁽³⁾) and nonlinear absorption behaviors of two α,ω-dithienylpolyenes with different conjugation length and two oligo(thienylvinylene) with different substituents on the thiophene rings have been studied using degenerate four wave mixing (DFWM) and nonlinear transmission techniques at 532 nm. The χ⁽³⁾ values of 1×10⁻³ mol/l solutions are all of the order of 10⁻¹³ esu. The χ⁽³⁾ values increase with the increase of the linear absorption coefficient. In addition, these compounds exhibit reverse saturable absorption for nanosecond laser pulses. The strength of reverse saturable absorption varies when the conjugation length and substituents change. Moreover, the nonlinear absorption characteristics of these compounds in the picosecond regime differ from those in the nanosecond regime. The different nonlinear absorption behavior is due to the relative contributions from excited singlet–singlet and triplet–triplet absorption. The strong reverse saturable absorption characteristics of two of the compounds suggest that they could be potential candidates for optical limiting applications in the nanosecond regime.     

新型Ru配合物三阶非线性光学性质的Z-扫描研究

通过Z-扫描的实验方法测量了几种新型的Ru配合物在460nm处的三阶非线性折射率n₂和非线性吸收系数β,并由此计算出它们的三阶非线性系数χ⁽³⁾.分析了分子结构对其三阶非线性光学性质的影响. 关键词：     

Investigation of third-order nonlinear optical susceptibility in polymer complexes of diarylidenealkanones

The third-order nonlinear optical susceptibility in polymer complexes of diarylidenealkanones has been investigated by the third harmonic generation technique at a wavelength of 1.06 μm. The macroscopic nonlinear susceptibility χ ⁽³⁾ measured is compared with the calculated γ values of the second-rank molar hyperpolarizability tensor. It is demonstrated that low-molecular chromophores can be used in syntheses of the stable polymer composite systems with a high nonlinear optical susceptibility. A further improvement in the nonlinear optical properties of complexes between deprotonated chromophores and high-basicity polymers can be achieved using the proposed methods. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 11, 2000, pp. 2099–2102. Original Russian Text Copyright ? 2000 by Ten’kovtsev, Yakimanski, Lukoshkin, Dudkina, Boehme.     

Giant nonlinear refraction in gold island films

Giant nonlinear refraction has been experimentally observed in gold island films. The real part of the third-order nonlinear susceptibility χ⁽³⁾(ω: ω,-ω, ω) reaches a value of about 10^?4 CGS units. The mechanism of nonlinearity of the refractive index can be associated with the resonance enhancement of the factor of the local optical field at the pump wavelength due to the excitation of surface plasmons, as well as with the contribution of the heating of conduction electrons in an ensemble of metal particles.     

Third-order nonlinear optical properties of thin sputtered gold films

Au films of thickness ranging between 5 and 52 nm were prepared by sputtering on quartz substrates and their third-order nonlinear optical response was investigated by Optical Kerr effect (OKE) and Z-scan techniques using 532 nm, 35 ps laser pulses. All prepared films were characterized by XRD, AFM and UV-VIS-NIR spectrophotometry while their third-order susceptibility χ⁽³⁾ was measured and found to be of the order of 10⁻⁹ esu. The real and imaginary parts of the third-order susceptibility were found in very good agreement with experimental results and theoretical predictions reported by Smith et al. [D.D. Smith, Y. Yoon, R.W. Boyd, Y.K. Cambell, L.A. Baker, R.M. Crooks, M. George, J. Appl. Phys. 86 (1999) 6200].     

Au:TiO2和Au:Al2O3纳米颗粒复合膜的线性和非线性光学特性

主要从实验和理论两个方面,探讨了不同Au颗粒尺寸和不同基质对Au：TiO₂和Au：Al₂O₃复合膜线性和非线性光学性质的影响.用吸收光谱研究了Au颗粒尺寸和基质与Au复合膜表面等离子体共振带之间的关系;用皮秒Z扫描技术研究了共振和非共振情况下(激发光波长分别为532nm和1064nm),Au颗粒尺寸和基质与复合膜三阶非线性极化率的关系.基于表面等离子体共振理论和局域场增强理论对复合膜进行了分析,得到了不同Au颗粒大小和不同基质时Au复合膜的 关键词： 金属纳米颗粒 复合膜 三阶非线性 表面等离子体共振     

Nonlinear optical properties of polymer-dispersed liquid-crystalline systems based on fullerene-doped 2-cyclooctylamino-5-nitropyridine

Holographic recording of thin diffraction gratings by nano-and picosecond laser pulses λ=532 nm) is studied in polymerdispersed liquid-crystalline structures based on photosensitive molecules of 2-cycloocty-lamino-5-nitropyridine sensitized with C₇₀ fullerene. Using experimental data, nonlinear refraction n ₂ and nonlinear third-order susceptibility χ⁽³⁾ are calculated for the first time. The obained values determine the potential of the studied media for the modulation and frequency generation of laser radiation in the visible spectral range.     

Third-order optical nonlinearities of lead-free (Na1−xKx)0.5Bi0.5TiO3 thin films

(Na_1−xK_x)_0.5Bi_0.5TiO₃ (NKBT) (x = 0.1, 0.2, and 0.3) thin films with good surface morphology and rhombohedral perovskite structure were fabricated on quartz substrates by a sol-gel process. The fundamental optical constants (the band gaps, linear refractive indices and absorption coefficients) of the films were obtained through optical transmittance measurements. The nonlinear optical properties were investigated by Z-scan technique performed at 532 nm with a picosecond laser. A two-photon absorption effect closely related with potassium-doping content was found in thin films, and the nonlinear refractive index n₂ increases evidently with potassium-doping. The real part of the third-order nonlinear susceptibility χ⁽³⁾ is much larger than its imaginary part, indicating that the third-order optical nonlinear response of the NKBT films is dominated by the optical nonlinear refractive behavior. These results show that NKBT thin films have potential applications in nonlinear optics.     

Third-order nonlinear optical properties of multiwalled carbon nanotubes modified by CdS nanoparticles

CdS nanoparticles were coated on the side wall of multiwalled carbon nanotubes (MWCNTs) by a wet chemical synthesis approach via noncovalent functionalization of MWCNTs with poly(diallyldimethylammonium chloride) (PDDA). The as-prepared material was characterized by X-ray diffraction (XRD), UV–vis absorption, fluorescence and transmission electron microscopy (TEM). The results indicated that CdS nanoparticles were uniformly coated on the surface of MWCNTs. Third-order optical nonlinearity of the as-prepared material was studied with the Z-scan technique with picosecond laser pulses at 532 nm. The Z-scan curve revealed that CdS nanoparticle-modified MWCNTs exhibited negative nonlinear refraction index and positive absorption coefficient. The real part and imaginary part of the third-order nonlinear susceptibility χ⁽³⁾ were calculated to be −4.9 × 10⁻¹² and 6.8 × 10⁻¹³ esu, respectively.