溶剂对N-{4-[(反式)-2-(4-硝基苯基)乙烯基]苯基}-N,N-二苯氨基分子双光子吸收特性的影响

在从头计算的基础上,利用两态模型对溶剂对N-{4-[(反式)-2-(4-硝基苯基)乙烯基]苯基}-N,N-二苯氨基分子双光子吸收特性的影响进行了理论研究.计算结果表明,溶剂对该分子的双光子吸收截面影响较大,双光子吸收截面随着溶剂极性的增加而增加.     

All-optical logic gates based on two-photon absorption in semiconductor optical amplifiers

When the two-photon absorption of a high intensity pump beam takes place in a semiconductor optical amplifier there is an associated fast phase change of a weak probe signal. A scheme to realize fast all-optical XOR logic function using two-photon absorption induced phase change has been analyzed. Rate equations for semiconductor optical amplifiers, for input data signals with high intensity, configured in the form of a Mach–Zehnder interferometer has been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The model shows that both XOR operation and pseudo-random binary sequence generation at 250 Gb/s with good signal to noise ratio is feasible.     

Role of doubled-frequency absorption in two-photon response of the Si MSM structure

The physical mechanism of two-photon response was studied in this paper by measuring characteristics of the two-photon response of the Si metal–semiconductor–metal (MSM) structure sample. The two-photon response includes two-photon absorption (TPA) and doubled-frequency absorption (DFA). An experiment was designed to measure the photocurrent dependence on incident light power, the dependence of the photoelectric signal on the applied voltage and the relationship between the photoelectric current and the light-spot position. The experimental fact that two-photon response of the silicon sample is relative to the applied electric field shows that DFA is the main physical mechanism of two-photon response and establishes the foundation for fabricating high-sensitivity two-photon response Si photodetector.     

All optical logic NAND gate based on two-photon absorption in semiconductor optical amplifiers

We propose a new scheme to realize all optical logic NAND operating at high speeds up to 250 Gb/s utilizing the ultrafast phase response during two-photon absorption (TPA) process in semiconductor optical amplifiers (SOA). NAND gate is important because other Boolean logic elements and circuits can be realized using NAND gates as basic building blocks. Rate equations for semiconductor optical amplifiers (for input data signals with high intensity) configured in the form of a Mach-Zehnder interferometer have been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The performance of this scheme is analyzed by calculating the quality factor of the resulting data streams. The results show that both AND and NAND operations at 250 Gb/s with good signal to noise ratio are feasible.     

Mathematical modeling of two-photon thermal fields in laser–solid interaction

In this paper, we have developed an analytical model to study the temperature distributions in IR optical materials heated by laser pulses. Our model takes into account the two-photon absorption (TPA). The calculations are based on a three-dimensional model of heat diffusion in solids using the integral transform method. We find out the rigorous analytical expression of the thermal field when one considers both one- and two-photon absorption. The model is valid for any laser–solid system whose interaction can be described by the generalized Beer–Lambert law. Specific results are presented for an application of the model to ZnSe sample. We find out that TPA can produce detectable temperature variation.     

Fluorescence upconversion properties of a class of improved pyridinium dyes induced by two-photon absorption

We report the fluorescence upconversion properties of a class of improved pyridinium toluene-p-sulfonates having donor–π–acceptor (D–π–A) structure under two-photon excitation at 1064 nm. The experimental results show that both the two-photon excited (TPE) fluorescence lifetime and the two-photon pumped (TPP) energy upconversion efficiency were increased with the enhancement of electron-donating capability of the donor in the molecule. It is also indicated that an overlong alkyl group tends to result in a weakened molecular conjugation, leading to a decreased two-photon absorption (TPA) cross section. By choosing the donor, we can obtain a longest fluorescence lifetime of 837 ps, a highest energy upconversion efficiency of 6.1%, and a maximum TPA cross-section of 8.74×10⁻⁴⁸ cm⁴ s/photon in these dyes.     

一种新的芴类衍生物的三光子吸收诱导荧光和光限幅效应研究

通过对新合成的芴的一种具有对称性衍生物4-2-(7-(4-氨基苯乙烯基)-9，9-二(2-乙基己基)-9H-芴-2-)乙烯基)苯胺(BASF)的DMF溶液的研究，发现其具有很强三光子吸收频率上转换荧光发射特性，实验测出上转换荧光的波长范围是456—775nm，在510nm处的荧光强度与入射光强的三次方成正比.在0.03mol/L的浓度下就有明显的三光子吸收诱导的光限幅效应.非线性吸收系数和吸收截面分别为γ=4.34×10^-20cm³/W²和σ₃＝2.4×10^-39cm⁶/W². 关键词： 三光子吸收 光限幅 上转换荧光 吸收截面     

Two-photon absorption and laser photolysis of trans-stilbene substitutes

The measured the two-photon absorption (TPA) cross sections of ethanol solution of trans-stilbene and its two substitutes excited by nanosecond radiation of the 2nd harmonic of a Nd:YAG laser (532 nm) are presented. To determine the TPA cross section, a method based on measurements of photochemical decomposition of molecules of the examined compounds having low photostability is suggested. The measured value of the TPA cross section of trans-stilbene in ethanol is found to be 25 GM, and the TPA cross sections of the trans-stilbene substitutes are found to be 60 and 70 GM. The TPA cross section of trans-stilbene substitutes obtained in the present paper is compared with the experimental and theoretical data obtained by other authors. The results of investigations demonstrate that the photochemical decomposition method can be successfully used to determine experimentally the two-photon absorption cross section of the compounds unstable under photoexcitation, including photochromatic molecules, biological objects, and radical photoinitiators.     

单光子和双光子激发的超歧化聚合物的光谱学特性研究

研究了二种新型超歧化聚合物在氯仿和二甲基甲酰胺溶剂中的飞秒激光单光子和双光子激发的光谱学特性．这二种聚合物是以苯为核、以对二甲氧基苯为连接单元，分别以二甲基苯胺为端基或以特丁基苯为端基的超歧化共轭聚合物．结果表明这种超歧化聚合物具有较大的溶剂极性相关的飞秒双光子吸收截面，不同的端基不仅影响分子内的电荷转移，而且导致超歧化分子共轭程度的变化．作为一种潜在的光学非线性材料，利用这种大的双光子吸收截面的超歧化聚合物可实现了飞秒双光子直写的三维高密度数据存储．     

UV-induced two-photon absorption in BiB3O6 single crystals

We show that BiB₃O₆ (BiBO) crystals, well known for their excellent second harmonic generation (SHG) properties, may also be of interest for third-order optical phenomena, particularly for two-photon absorption (TPA). Photoinduced TPA measurements were performed under illumination of excimer Xe–F laser (λ = 217 nm) as a photoinducing (pumping) beam. It created a thin surface layer (about 85 nm) that was a source of the observed photoinduced TPA. Raman shifted Nd-YAG laser radiation (λ = 1.9 μm) as well as its second and fourth harmonics (λ = 950 and λ = 475 nm, respectively) were used as fundamental (probing) beams of the TPA. The highest values of the TPA β coefficient were achieved for a polarization of the pumping light directed along crystallographic axis b. Quantum chemical simulations indicate on substantial contribution of UV-induced electron–phonon anharmonicity to the observed TPA. The obtained values of TPA coefficients indicate a possibility of using BiBO crystals as UV-operated optical limiters in a wide spectral range.     

Two-photon absorption coefficient in relation to the typical pulse models of laser

The two-photon absorption (TPA) coefficient (β) relating to pulse models of laser is theoretically studied based on the nonlinear absorption equation. An expression of nonlinear energy transmission is obtained, in which a factor (g) is introduced to describe the β deviation resulting from the pulse profile of laser. The relative deviation can be then expressed as (1/g − 1)% for comparing β obtained based on other pulse models of laser with β₀ based on the rectangular one. The values of g factor and the deviation of some typical ultra-short pulse models used nowadays are also calculated and presented. Our results suggest that the β deviations from the temporal pulse shapes should not be neglected in usual nonlinear transmission measurement. The g factor may become a useful parameter in taking account of this deviation.     

Enhancement of two-photon absorption and photoinduced birefringence in methyl orange by Au nanoparticles

Two-photon absorption and photoinduced anistropy of a methyl orange/Au nanoparticles composite system were investigated. Open aperture Z-scan measurements demonstrated that the absorption cross section of methyl orange in an Au colloid solution can increase 42-fold compared to purified that of a methyl orange aqueous solution. Meanwhile, a 2.6-fold enhancement of the photoinduced birefringence of methyl orange in the presence of Au was also observed. The mechanism accounting for the enhancement of two-photon absorption coefficient and photoinduced birefringence was discussed in terms of the localized field effect via surface plasmon resonance of Au nanoparticles, which was further confirmed using the fluorescence spectrum technique.     

The radiative lifetime and the optical absorption cross section measurements of neodymium

Using the technique of laser induced fluorescence, we have obtained the experimental results that the radiative lifetime of the ~7K_3~o state and the optical absorption cross section of the transition ~5I_4~e→~7K_3~o of neodymium are 675±50ns and (1.48±0.74)×10~(-13)cm~2 respectively.     

光学-射频双光子耦合作用下的电磁诱导透明和电磁诱导吸收

在通常的Λ型三能级系统中,光学耦合场和探测场分别激发两个不同的光学跃迁,探测吸收谱呈现电磁诱导透明(EIT)特性.若将此系统拓展为光学-射频双光子耦合场和探测场共同作用下的准Λ型四能级系统,探测吸收谱呈现电磁诱导吸收(EIA)和EIT两种特性.通过求解系统的密度矩阵方程,分析了EIA和EIT的产生条件,并给出了相应的缀饰态解释.研究结果表明,在准Λ型四能级系统中,光学耦合场对EIA和EIT的形成起决定作用,共振时出现EIA,非共振时出现EIT,而且EIA和EIT的线宽随着光学耦合场拉比频率的增大而增加. 关键词： 电磁诱导透明 电磁诱导吸收 射频场 光学耦合场     

Functional polymers by two-photon 3D lithography

In the presented work, two-photon 3D lithography and selective single-photon photopolymerization in a prefabricated polydimethylsiloxane matrix is presented as an approach with potential applicability of waveguide writing in 3D by two-photon polymerization.Photopolymers based on acrylate chemistry were used in order to evaluate the optical capabilities of the available two-photon system. Several photoinitiators, tailored for two-photon absorption, were tested in a mixture of trimethylolpropane triacrylate and ethoxylated trimethylolpropane triacrylate. Best results were obtained with a recently synthesized diynone-based photoinitiator. Feature resolutions in the range of 300 nm were achieved. Due to the cross-conjugated nature of that donor-π-acceptor-π-donor system a high two-photon absorption activity was achieved. Therefore, a resin mixture containing only 0.025 wt% of photoinitiator was practical for structuring by two-photon polymerization. The required initiator content was therefore a factor of 100 lower than in traditional one-photon lithography.The aim of the second part of this work was to fabricate optical waveguides by selectively irradiating a polymer network, which was swollen by a monomer. The monomer was polymerized by conventional single-photon polymerization and the uncured monomer was removed by evaporation at elevated temperatures. This treatment leads to a local change in refractive index. Refractive index changes in the range of Δn = 0.01 (Δn/n = 0.7%) were achieved, which is sufficient for structuring waveguides for optoelectronic applications.     

一种新型有机染料HEASPS在不同波长时的双光子吸收和频率上转换性质研究

报道了一种新型双光子吸收染料 ,即反式 - 4- [4′- (N-羟乙基 - N-乙基胺基 )苯乙烯基 ]- N-甲基吡啶对甲苯磺酸盐的非线性光学性质 ;测试了染料在 72 0～ 110 0 nm波段的非线性透过率曲线。结果发现 :双光子吸收最强波长相对线性吸收峰波长的两倍处有明显蓝移 ;计算出的相应波长的双光子吸收截面在 930 nm处染料有最大双光子吸收截面(2 .0 6× 10 - 4 7cm4·s/ photon) ;测量了染料在 90 0～ 110 0 nm波段的上转换效率 ,在 10 2 0 nm处有最高效率 (5 .1% ) ,最高激射效率的波长相对最强双光子吸收的波长有明显红移     

Influence of two-photon absorption on bistable switching in a silicon photonic crystal microcavity

By employing a simplified nonlinear coupled mode theory, we discuss the influence of two-photon absorption (TPA) on the characteristics of bistable switching. It is revealed that the critical value of frequency detuning for bistability rises linearly with increasing TPA coefficient k (when k is less than 30), and eventually access to a saturated value. It is also found that TPA effect will be enhanced for a greater frequency detuning, especially when transmission reaches its peak value. As a result, the peak transmission will decrease monotonously with the increasing frequency detuning. Based on this simplified model, the TPA-induced temperature rise in microcavity is also estimated. The theoretical predictions show good agreement with the simultaneous results, as well as the proposed experimental phenomena.     

External electric field induced modulation instability of an electromagnetic beam in two-photon photorefractive materials

The modulation instability of a broad electromagnetic beam in a biased two-photon photovoltaic photorefractive material, due to two-photon-photorefractive effect has been investigated. The one-dimensional modulation instability growth rate has been estimated under the linear stability framework. The behavior of the gain spectrum is different in low and high power regions. It has been predicted that, with the application of external electric field, it is possible to initiate and control growth of the instability in those media, where modulation instability was hitherto prohibited. The influence of different system parameters on the instability growth rate has been examined.     

基于太阳光谱的NO2浓度反演方法

 构建了一套光谱测量系统,以太阳光为光源,利用高精度成像光谱仪采集太阳光谱,选取某一时刻的太阳光谱为参考,结合当时的污染气体浓度数据,应用差分吸收原理,反演出其他任意时刻的NO2浓度。运用Origin7.5软件进行光谱解析,根据HITRAN数据库绘制吸收截面谱,并获取指定数值的应用,实现了对光谱谱线的定量分析,并且误差小。该反演过程具有光谱处理失真低以及反演参量精度高的特点,一定程度上提高了太阳光谱反演气体浓度的精度。实验结果与其他设备测量结果一致,证实了该方法的可行性。     

Transition Dipole,Charge Transfer,and Electron-hole Coherence in Two-photon Absorption: Visualizations with Two Dimensional Site and Three Dimensional Cube Representations

采用二维和三维实空间分析方法可视化了双光子吸收特征,包括跃迁距、电荷转移和电子空穴相干性. 跃迁密度的三维实空间分析揭示了跃迁距的强度和方向,电荷差异密度显示双光子吸收过程中的电荷转移方向. 跃迁密度矩阵的二维实空间分析可视化了电子和空穴的相干性. 二维和三维实空间分析有助于清晰地理解双光子吸收的电荷转移过程和激发的分子单元对双光子吸收的贡献.