NONLINEAR EXCITED STATE ABSORPTION IN CADMIUM-PORPHYRIN-LIKE

Nonlinear absorption at 532 nm in a cadmium texaphyrin solution has been studied using 8ns and 23ps laser pulses. The experiments show that reverse saturable absorption occurs in the nanosecond case. For picosecond pulses, RSA occurs only at low fluences, and saturable absorption occurs at high fluences. A six-level model is proposed to explain these nonlinear absorption effects. Several photophysical parameters of excited states for cadmium texaphyrin, such as absorption cross-sections at 532nm and lifetime, have been evaluated by fitting theoretical calculations with the experimental results.     

萘酞菁铅化合物的光限幅特性研究

应用调Q倍频ns/ps Nd：YAG脉冲激光,在波长为532nm,脉冲宽度为8ns,重复频率为1Hz的条件下,研究了溶于二甲基亚砜(DMSO)中的萘酞菁铅溶液的反饱和吸收和光限幅特性。实验表明,萘酞菁铅具有良好的光限幅特性,它的有效激发态吸收截面与基态吸收截面的比值约为15．21,大于萘酞菁铜。研究结果表明,萘酞菁铅的光限幅特性优于C60,激发态吸收是其主要的光限幅机理。实验结果证实了重原子效应可以通过增强系际跃迁而使三重态的反饱和吸收增强,从而提高光限幅的能力。     

利用双光子吸收效应测量激光脉冲的相干时间

研究了利用反向泵浦－探测双光子吸收材料的方法来测量脉冲激光的相干时间，并测量量了２３ｐｓ，５３２ｎｍ Ｎｄ：ＹＡＧ激光脉冲的相干时间。实验和理论分析表明，光束相干作用增加了双光子吸收，利用此方法可测量其它脉宽激光的相干时间。     

基于反饱和吸收和自聚焦两种效应的光限幅器

用酞菁铜金属有机染料首次演示了基于反饱和吸收和自聚焦两种效应的光限幅器．实验和理论分析表明，这种限幅器的输入阈值功率由反饱和吸收决定，而自聚焦使限幅器的最大限幅输出功率降低，限幅效果显著增强．     

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.     

Optical Limiting and ExcitedState Nonlinear Optical Properties in Lead Phthalocyanine

1.IntroductionLeadphthalocyaninehasreceivedconsiderableattentionasitexhibitsstrongreversesaturableabsorption(RSA)behaviorLI].Thiskindoforganometalliccompoundcanbeusedasopticallimitingdevicetoprotecteyesandsensorsfromlaserhazard.Thenanosecondopticallimitingpropertyofleadphthalocyaninehasbeeninvestigatedyet[2].Inthispaper,thepicosecondopticallimitingbehaviorofleadphthalocyanine(Pbpc(CP)4)ispresentedandtheresultiscomparedwithC6o,areversesaturableabsorptionmaterialwhichhasbeenwidelystudied.The…     

酞菁铜非共振反饱和吸收的稳态特性

酞菁铜溶液在波长532nm调Q激光作用下,实验获得反饱和吸收特性.在稳态条件下,用速率方程理论推得分别描述薄样品和厚样品的反饱和吸收特性的两个解析式,理论分析与实验结果一致.     

Experimental investigation of optical limiting and thermal lensing in toluene solutions of C70

Optical limiting and thermal lensing studies are carried out in C₇₀-toluene solutions. The measurements are performed using 9-ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm. Optical limiting studies in fullerene molecules lead to the conclusion that reverse saturable absorption is the major mechanism for limiting. Analysis of thermal lensing measurements showed a quadratic dependence of thermal lens signal on incident laser energy, which also supports the view that optical limiting in C₇₀ arises due to sequential two-photon absorption via excited triplet state (reverse saturable absorption).     

Investigation of Cr:YAG passive mode-locking in a pulsed Nd:YAG laser

Passive mode-locking of a pulsed Nd:YAG laser using a Cr⁴⁺:YAG saturable absorber was realized for the first time in a nearly critical stable resonator containing an antiresonant ring structure. The output energy and pulse duration are 13.5 mJ and 180 ps, respectively. The recovery time and saturable intensity for excited-state absorption of Cr⁴⁺:YAG under the action of strong laser pulses were calculated from rate equations.     

Nonlinear optical response of Au and Ag nanoparticles doped polyvinylpyrrolidone thin films

Colloidal Au and colloidal Ag were prepared by chemical reaction method and the nonlinear optical properties of Au and Ag nanoparticles doped polyvinylpyrrolidone (PVP) composite films were investigated using Z-scan technique with 38 ps pulses at 532 nm. Open aperture Z-scan measurements indicated that both the Au/PVP and Ag/PVP composite films exhibited reverse saturable absorption. Nonlinear absorption coefficients and third-order nonlinear refractive indices were determined. The mechanisms accounting for the process of nonlinear refractions were analyzed and the figures of merit W and T of the Au/PVP and Ag/PVP composite films were evaluated.     

有机分子激发态非线性吸收的瞬态特性研究

提出了一种通过测量单脉冲光的输入与输出波形来研究激发态非线性吸收的新方法，用这种方法研究了纳秒脉作用下类卟啉镉溶液与甲基橙溶液的三重激发态的非线性吸收特性，前者为反饱和吸收现象，后者是由饱和吸收转化为反饱和吸收的新现象，实验结果验证了理论模拟和正确性。     

Photophysical and nonlinear optical properties of an azobenzene substituted zinc phthalocyanine

Photophysical property and third-order optical nonlinearity of an azobenzene substituted zinc phthalocyanine (azo-ZnPc) in chloroform solution were studied by UV–Vis spectra method and a picosecond Z-scan technique at 532 nm with pulse duration of 25 ps, respectively. It was found that the azo-ZnPc shows large positive nonlinear refraction and positive nonlinear absorption, exhibiting the defocusing effect and reverse saturable absorption, respectively. The molecular second hyperpolarizability of the azo-ZnPc dyad was measured to be 3.9 × 10⁻³⁰ esu. All the results suggest that the studied azo-ZnPc dyad may have potential applications in the field of nonlinear optics.     

EXCITED-STATE NONLINEAR ABSORPTION AND ITS APPLICATION IN PHOTONIC TECHNOLOGY

The main achievements in our research on the physical phenomena of the excited-state nonlinear absorption in a molecular system and its applications in photonic technology are described. In the first part of this paper, some energy-level models and rate-equations are used to explain various mechanisms of the excited-state nonlinear absorption under differ-ent conditions, such as reverse saturable absorption caused by the triplet and/or the singlet excited-state absorption; saturable absorption due to the first and/or the second singlet excited-state absorption; and the excited-state nonlinear absorption induced by two-photon absorption. The experimental results for metal-organic and C₆₀ materials irradiated by ps and ns laser pulses are consistent with the simulated curves of the transmittance versus flu-ences. In the second part, the applications of excited-state nonlinear absorption in photonic techniques including optical bistability, optical switching, optical limiting, optical modula-tion, optical logic and optical storage are introduced. The working principles of the photonic devices based on the excited-state nonlinear absorption are presented. The experimental characteristic curves are found in good agreement with the theoretical simulations for these devices.     

酞菁铜染料的反饱和吸收动力学

本文用速率方程研究了酞菁铜染料氯仿溶液的反饱和吸收的动力学过程,并用YAG倍频调Q脉冲激光入射该样品,验证了理论.通过理论曲线与实验结果的拟合,估算出酞菁铜三重态激发态的吸收截面为2.6×10~(-17)cm~2.     

Diode end-pumped passively mode-locked Nd:YLF laser at 1047 nm using single-wall carbon nanotubes based saturable absorber

A single-wall carbon nanotubes based saturable absorber wafer with absorption wavelength around 1047 nm was fabricated by electric Arc discharge method and employed in a diode end-pumped Nd:YLF laser as saturable absorber. Passively continuous wave mode-locking oscillation was achieved in the pump range form 6.7 to 8.0 W. The duration and repetition rate of the mode-locked pulses were 10 ps and 59 MHz, respectively. The average output power was 280 mW.     

Analysis of effect of excitation pulse characteristics on numerical simulation of reverse saturable absorption

We present the results of analysis of rate equations for reverse saturable absorption (RSA) process to understand the applicability and probable errors in using only time dependence of the excitation pulse as against both space and time dependence in numerical simulations of rate equations. We have considered a three-level approximation of the five-level rate equations under nano-second laser pulse excitations. The population density, nonlinear absorption and transmission have been calculated and compared for different approximations and for different excitation pulse spatial shapes. We show that the neglect of spatial characteristics of the excitation pulses in the rate equation analysis can lead to considerable errors in the numerical simulations of RSA in case of excitation fluences below the fluence for saturation of transmission.     

1-(2-吡啶偶氮)-2-萘酚薄膜的非线性光学特性研究

运用Ｚ扫描方法研究了１－（２－吡啶偶氮）－２－萘酚薄膜的非线性光学特性。用皮秒脉冲激光测得在５３２ ｎｍ 处、光强较低时χ（３）Ｒ ＝ １．２９×１０－ ９ ｅｓｕ, β＝ ４２ ｃｍ ／ＧＷ; 同时研究了不同光脉冲能量时的非线性吸收特性, 发现其非线性吸收随着光强的增大由反饱和吸收转为饱和吸收     

High power subpicosecond pulse generation from a synchronously pumped dye laser combined with an external compressor

A new scheme of subpicosecond pulse generation based on a dye laser is described. Output pulses of 15 ps from a rhodamine-6G laser pumped synchronously by a frequency-double mode-locked Nd: YAG laser are compressed into 0.8 ps pulses of 2 MW by two passes of saturable absorber (DODCI) and saturable amplifier (rhodamine-6G). The technique is useful for generating widely tunable, high power repetitive subpicosecond pulses.     

Optical limiting and pulse reshaping of picosecond pulse trains by fullerene C60

We present a dynamical theory of nonlinear absorption and propagation of a laser pulse train that contains 20 subpulses with an individual pulse width of 100 ps. It is shown that the accumulative nonlinearity and the reverse saturation absorption play important roles in the optical limiting performance and pulse shaping. When the incident field is not too strong, the population transfer reveals a slow response process, and the periodic sequence of short light pulses can be regarded as a continuous long pulse. The general theory is applied to fullerence C₆₀, which is a popular reverse saturable absorption material and a good limiter because of its larger excited-state absorption cross-section compared with that of the ground state. The propagation of the front subpulses is mainly affected by the linear transition between the ground state and the first excited singlet state, while the latter subpulses are attenuated by the excited-state absorption. Moreover, these two different kinds of absorption mechanisms result in different radial distributions for different subpulses. The pulse propagation is studied by solving numerically the coupled rate equations and the propagation equation of the optical pulse intensity, using experimental parameters as input. We suggest a new method to measure the lifetime of the triplet state.     

锌酞菁配合物的线性与非线性光学性质研究

利用UV-Vis吸收光谱、荧光光谱及开孔Z扫描技术对五种锌酞菁配合物的DMF溶液进行了线性与非线性光学性质的表征;并以无取代锌酞菁为例,研究了酞菁溶液线性与非线性光学性能的浓度效应。结果表明五种酞菁均具有显著的荧光和非线性光学效应,其非线性吸收系数在10-9 cm·W-1数量级范围。且随酞菁浓度的改变,其荧光和非线性吸收明显改变,表现出强烈的浓度效应。