Strong optical limiting property of a ball-type supramolecular zinc-phthalocyanine in polymer-phthalocyanine composite film

The nonlinear absorption and optical limiting (OL) performance of a supramolecular hexa-phthalocyaninato-hexazinc (II) with hexylthio substituents in solution and in the solid-state have been described using the open-aperture Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The results indicated that OL performance of the investigated compound in the polymeric film is much better compared to properties in solution. With the excellent combination of OL parameters the investigated compound in the solid-state is a candidate for the use as optical limiter.     

Optical limiting properties of trimeric metallo-phthalocyanines/polymer composite films

The nonlinear absorption and optical limiting properties of two trimeric metallo-phthalocyanines namely, 2,4,6-tris[2-oxa-9,10,16,17,23,24-hexa(hexylthio) phthalocyaninato M(II)]-s-triazine (M=Zn for compound ZnPc and Cu for compound CuPc) doped polyvinyl chloride (PVC) thin film in the nanosecond regime were investigated by using the open-aperture Z-scan technique. The measurements were performed using 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. OL parameters of the ratio of the excited state to ground state absorption cross-sections κ, the effective nonlinear absorption coefficient β_eff, the linear absorption coefficient α₀ and the saturation density or energy density F_sat values were determined. The results show that MPc/PVC composite displays much larger nonlinear absorption coefficient and lower saturable fluence for optical limiting when compared to the same Pc molecules in solution. The results indicated that both compounds exhibited good OL performances. ZnPc shows slightly better OL parameters than that of CuPc.     

Optical limiting response by embedding copper phthalocyanine into polymer host

The multilayer film of PMMA containing mononuclear octakis(mercaptopropylisobutyl-POSS) substituted phthalocyaninato-copper (CuPc) was obtained by spin-coating on quartz substrate. The nonlinear absorption and optical limiting (OL) performance of CuPc have been described using the open-aperture Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The results indicate that CuPc/PMMA composite exhibits a much larger nonlinear absorption coefficient, a lower saturable fluence and a lower absorption cross-section ratio for optical limiting when compared to the same CuPc molecules in solution. No evidence of film fatigue or degradation was observed in the CuPc/PMMA film after numerous scans at varying laser intensity. This material is a good candidate for optical limiting applications.     

Trimeric metallo-phthalocyanines with good performances for nanosecond optical limiting in solution

Optical limiting (OL) performances of two trimeric metallo-phthalocyanines namely, 2,4,6-tris[2-oxa-9,10,16,17,23,24-hexa(hexylthio) phthalocyaninato M(II)]-s-triazine (M = Zn for compound ZnPc and Cu for compound CuPc) were investigated by using the Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. OL parameters of the ratio of the excited state to ground state absorption cross-sections κ, the effective non-linear absorption coefficient β_eff, the linear absorption coefficient α₀, limiting threshold F_th and the saturation density or energy density F_sat values were determined for the investigated compounds. The results indicated that both compounds exhibited good OL performances. ZnPc shows slightly better OL parameters than that of CuPc.     

Third order optical nonlinearities of eight-β-octa-octyloxy-phthalocyanines

The third order nonlinear optical properties of the eight-β-octa-octyloxy-phthalocyanines in chloroform were investigated by Z-scan using ps laser at 532 nm. The excited state absorption cross section and the nonlinear refractive cross-section were determined. Eight-β-octa-octyloxy-phthalocyanine free base and eight-β-octa-octyloxy-nikle-phthalocyanine both posses large σ_es/σ₀ ratio and positive σ_r, and the introduction of nikle ion reduces these values. Optical limiting performance was studied using multi-level model, the result shows that eight-β-octa-octyloxy-phthalocyanine free base has a much lower limiting threshold.     

OPTICAL LIMITING EFFECT IN TWO PHTHALOCYANINES OBSERVED BY PICOSECOND PULSED LASER

Optical limiting (OL) properties of two phthalocyanines were investigated by using picosecond laser pulses at 532nm. The relative ratios k of the absorption cross section of the first singlet excited state to that of the ground state were approximately obtained by the analysis of the experimental results in which the reverse saturable absorption model of the three-energy-level scheme was employed. A significant comparison with fullerene C₆₀ was presented for OL. The OL mechanisms have been analysed in detail.     

The nonlinear refraction and nonlinear absorption in 4-(4,6-diaminopyrimidin-2-ylthio) substituted double-decker Lu(III) phthalocyanine

A 4-(4,6-diaminopyrimidin-2-ylthio) substituted double-decker Lu(III) phthalocyanines (4) have been prepared and characterized by elemental analysis, IR, UV-vis and ¹H NMR spectroscopies. The nonlinear refractive index, nonlinear absorption and the optical limiting (OL) performance of the compound 4 in a 0.5 mm spectroscopic cell in DMF solution were investigated by using 4 ns pulse laser at 532 nm. Z-scan experiments have been conducted between 0.24 and 2.39 GW/cm² peak intensities for 10 Hz repetition rate and also between 2.39 and 23.89 GW/cm² peak intensities for 1 Hz repetition rate. The thermal effect contributes to the nonlinear response of the material higher than 0.72 GW/cm² peak intensity at 10 Hz. We measured the effective nonlinear refractive index of the material as 1.2×10⁻¹¹ esu at 3.5×10⁻⁴ M concentration with the peak intensity less than 0.72 GW/cm² and we found that nonlinear absorption was very small. On the other hand, when concentration is increased to 2.4×10⁻³ M material's nonlinear absorption becomes dominant mechanism for the nonlinear response and the compound 4 indicates OL behavior at 2.4×10⁻³ M concentration.     

Influence of radiation cross section uncertainties on shock wave structure

This numerical study investigates the sensitivity of non-equilibrium shockwave structure to uncertainties in (a) the ground and excited state continuum radiative cross section and (b) the bound-bound radiative cross section in a three level (ground, excited, and free electronic states considered) argon-like gas at Mach 18 and a pressure of 1 cm Hg. Changing the values of the radiative cross sections by an order of magnitude does not significantly influence the relaxation region; however, a large change occurs in not only the magnitude but also the extent of both the electron and excited state precursors. Increasing either the ground state continuum or the bound-bound cross section decreases the number of free electrons in front of the shock wave. These cross sections also influence the extent of the electron precursor through their influence on the ratio of the electrons produced by ground state photoionization to those produced by ground state photoexcitation followed by excited state photoionization. The bound-bound cross section also controls the excited state precursor, because the production of excited states is entirely due to line radiation. Increasing the excited state photoionization cross section increases both the magnitude and extent of the electron precursor, because the cross section influences the ratio of the two processes that compete to produce free electrons, and at the same time it influences the magnitude of the excited state precursor.     

Measurements of photoionization cross sections from the 4p, 5d and 7s excited states of potassium

New measurements of the photoionization cross sections from the 4p ²P_1/2,3/2, 5d ²D_5/2,3/2 and 7s ²S_1/2 excited states of potassium are presented. The cross sections have been measured by two-step excitation and ionization using a Nd:YAG laser in conjunction with a thermionic diode ion detector. By applying the saturation technique, the absolute values of the cross sections from the 4p ²P_3/2 and 4p ²P_1/2 states at 355 nm are determined as 7.2±1.1 and 5.6±0.8 Mb, respectively. The photoionization cross section from the 5d ²D_5/2,3/2 excited state has been measured using two excitation paths, two-step excitation and two-photon excitation from the ground state. The measured values of the cross sections from the 5d ²D_5/2 state by two-photon excitation from the ground state is 28.9±4.3 Mb, whereas in the two-step excitation, the cross section from the 5d ²D_3/2 state via the 4p ²P_1/2 state and from the 5d ²D_5/2,3/2 states via the 4p ²P_3/2 state are determined as 25.1±3.8 and 30.2±4.5 Mb, respectively. Besides, we have measured the photoionization cross sections from the 7s ²S_1/2 excited state using the two-photon excitation from the ground state as 0.61±0.09 Mb.     

Optical Limiting Properties of Two Soluble Polymer/Multi-Walled Carbon Nanotube Composites

Two soluble polymer grafted multi-walled carbon nanotubes （MWNTs）, including poly（N-vinylcarbazole）-MWNTs and poly（methyl methacrylate）-MWNTs, are synthesized. Their nonlinear optical properties and opticaJ limiting （OL） performances are investigated by z-scan method with 527nm nanosecond laser pulses. These grafted MWNTs dissolved in chloroform show much better optical limiting performance than those of MWNTs and C60 in toluene solution. Nonlinear absorption and nonlinear scattering mechanism are taken into consideration for explaining the observed results. The comparison of the experimental results shows that nonlinear absorption is the dominant mechanism for OL performance of these new samples.     

一种新型有机金属化合物纳秒时域饱和吸收特性研究

合成了一种新型有机金属配合物Cetyltrimethylammonium-bis(2-thioxo-1,3- dithiole- 4,5-dithiolato)-copper(简称CtCu)材料.采用单光束Z扫描测试技术,在波长为1 053 nm,脉宽为1 ns的条件下研究了该样品的三阶非线性光学性质.研究发现,该材料具有很强的饱和吸收特性,激发态的有效吸收截面为σeff＝1.10×10－19 cm2,与基态吸收截面的比值为1∶484.利用非线性透过率实验验证了材料的饱和吸收特性,并对其产生机理进行了分析.实验结果表明,该材料在近红外波段的激光脉冲压缩方面有潜在的应用前景.     

强非线性吸收下Z扫描衍射模型及实验研究

根据光的衍射理论,建立了非线性光学介质对高斯光束的开孔Z 扫描理论模型.数值计算表明,当相移比值Γ≤0.15,出射光功率随入射光功率的增加出现振荡衰减现象;当Γ>0.15,在输入光强低于某一个值时,输出随输入的增加而线性增加;当输入光强超过该值后,输出功率不再增加甚至趋于零.实验采用Nd∶YAG脉冲激光,在波长为532 nm,脉宽8 ns条件下,对含3.5%和7.0%碳纳米管的聚苯胺/碳纳米管复合体薄膜（PANI/MWCNT）的非线性吸收特性进行了研究.计算表明,该类化合物的激发态吸收截面积远大于其基态吸收截面积,具有很强的反饱和吸收.     

Direct measurements of nonlinear absorption and refraction in solutions of phthalocyanines

We report direct measurements of the excited singlet state absorption cross section and the associated nonlinear refractive cross section using picosecond pulses at 532 nm in solutions of phthalocyanine and naphthalocyanine dyes. By monitoring the transmittance and far field spatial beam distortion for different pulsewidths in the picosecond regime, we determine that both the nonlinear absorption and refraction are fluence (energy per unit area) rather than irradiance dependent. Thus, excited state absorption (ESA) is the dominant nonlinear absorption process, and the observed nonlinear refraction is also due to real population excitation.     

Nonlinear absorption of CS2 at the wavelength of 400 nm with femtosecond pulses

Nonlinear absorption of carbon disulfide (CS₂) was investigated by Z-scan technique and time-resolved pump-probe technique with femtosecond pulses at 400 nm wavelength. By the two techniques, we confirmed that the nonlinear absorption of CS₂ arise from a combination of two-photon absorption (TPA) and the excited state absorption induced by TPA under the incident laser pulses with 400 nm wavelength. The coefficient of TPA, the absorption cross-section of low excited state and lifetime of low excited state were obtained by theoretical fitting the experimental results. The results indicated that the CS₂ has good optical limiting capability at 400 nm wavelength.     

Wavelength dependent resonant nonlinearities in a standard saturable absorber IR26 on picosecond time scale

Nonlinear optical properties of a standard dye IR26 have been studied by using the Z-scan technique to decipher the difference in the mechanism of nonlinear absorption on picosecond time scale at two wavelengths i.e. at 1064 nm and 532 nm. A prominent contribution of nonlinear absorption is observed in the Z-scan profiles at 1064 nm. The dye exhibits the mechanism of self-defocusing at 1064 nm in contrast to that of self-focusing at 532 nm. While the two photon absorption has been found to be the dominant mechanism of reverse saturable absorption at 1064 nm, the mechanism of excited state absorption is operating at 532 nm. Additionally, the optical phase conjugate geometry of degenerate four wave mixing (DFWM) technique has been used to measure the third order nonlinear susceptibility values at 532 nm to compare with those obtained from the Z-scan profiles.     

Impurity and exciton effects on the nonlinear optical properties of a disc-like quantum dot under a magnetic field

A detailed investigation of the nonlinear optical properties of the (D⁺, X) complex in a disc-like quantum dot (QD) with the parabolic confinement, under applied magnetic field, has been carried by using the perturbation method and the compact density-matrix approach. The linear and nonlinear optical absorption coefficients between the ground (L = 0) and the first excited state (L = 1) have been examined based on the computed energies and wave functions. The competition between the confinement and correlation effects on the one hand, and the magnetic field effects on the other hand, is also discussed. The results show that the confinement strength of QDs and the intensity of the illumination have drastic effects on the nonlinear optical properties. In addition, we note that the absorption coefficients of an exciton in QDs depend strongly on the impurity but weakly on the magnetic field. Furthermore, the light and heavy hole excitons should be taken into account when we study the optical properties of an exciton in a disc-like QD.     

The primary investigation of optical-limiting effects of optical active phthalocyanine derivative TMBO-SiPc

The optical-limiting property of an optically active phthalocyanine derivative with different configuration in chloroform solution was measured at 532 nm with 10 ns pulses. The excited state absorption cross-section σ_ex of the derivative was determined with the Z-scan technique. The results showed that the phthalocyanine derivative possesses larger σ_ex than the ground state absorption cross-section σ₀, indicating that it is a material for reverse saturable absorption. And it is specially noticed that the change in the optically active configuration affects its optical-limiting property significantly.     

Photophysical studies on axially substituted indium and gallium phthalocyanines upon UV-Vis laser irradiation

A series of results from different photophysical experiments on indium and gallium phthalocyanine (Pc) compounds is reported. Gallium Pc's have much longer singlet and triplet excited state lifetimes in comparison with indium Pc's. The strong reverse saturable absorption observed at 532 nm excitation is a consequence of the increase in absorbance of Pc's in the triplet excited state in the optical window comprised between Q- and B-bands, as verified upon laser irradiation with ns pulses at 355 nm. Using C₆₀ as a reference, the intersystem cross quantum yields of tBu₄PcInCl and tBu₄PcGaCl are 0.70 and 0.36, respectively.     

二苯乙烯衍生物分子双光子吸收截面：官能团对称性的影响

选取了具有不同对称性的二苯乙烯系列衍生物分子，在HF水平上，利用响应函数方法，研究了该系列分子的单光子和双光子特性. 研究结果表明，该系列分子具有较强的双光子特性. 在可见光范围内，反对称分子的最大双光子吸收态是第一激发态，而对称分子的最大双光子吸收出现在第四激发态. 相对于对称分子而言，反对称分子具有更大的双光子吸收截面. 因此，分子的对称性是否比不对称性更有利于增大分子的双光子吸收截面，还与分子的π中心部分的特性有关. 还给出了电荷转移态的电荷迁移过程. 关键词： 双光子吸收 响应函数方法 非线性光学     

Enhanced optical limiting properties in suspensions of CdO nanowires

Optical limiting (OL) properties of CdO nanowires in water and ethanol were investigated by using nanosecond laser pulses at 532 nm. Experimental results show that suspension of CdO nanowires in ethanol exhibits better OL property than solution of C₆₀ in toluene and suspension of CdO nanowires in water. The dominant mechanism for the observed enhanced optical limiting in ethanol suspensions of CdO nanowires is due to nonlinear scattering.