Dispersive white light continuum single Z-scan for rapid determination of degenerate two-photon absorption spectra

Abstract

We present an experimental technique to determine the degenerate two-photon absorption (2PA) spectra by performing a single Z-scan using a high-spectral-irradiance white light continuum (WLC) generated by a hollow core fiber. The hollow fiber was filled with Argon (Ar) gas at a pressure of 0.6 bar and was pumped with 500 mJ, 30 fs, and 800 nm pulses. The broadband WLC pulses with 350 nm bandwidth in the range of 600-950 nm were compressed to sub-8 fs pulses. To characterize and interpret the data obtained from this method, the spectral, temporal and spatial characteristics of the WLC were first analyzed. The WLC emerging from the compressor was dispersed using a prism pair and then focused into the sample by a cylindrical lens. Since different spectral components are spatially separated, any part of the sample in the beam cross section is irradiated with almost single wavelength pulses leading to only a degenerate 2PA process. The nonlinear transmittance was then measured by a charge-coupled-device (CCD) line camera as a function of the sample position while the sample was moved along the beam direction by a motorized translation stage. In this way the Z-scans at different wavelengths in the WLC spectral range can be measured and thus the wavelength-resolved degenerate 2PA spectra can be obtained by performing a single scan using dispersive WLC. This method was verified on a well-characterized dye Rhodamine B and yield a reasonable agreement with the data found in the literature. We used this method to determine the 2PA spectra of some two-photon initiators (2PIs) developed for two-photon polymerization (2PP) based 3D micro-structuring.

Flexible and Transparent Oligothiophene-o-Carborane-Containing Hybrid Films for Nonlinear Optical Limiting Based on Efficient Two-Photon Absorption

“…Using the open aperture Z-scan configuration, the nonlinear absorption coefficient (β) of the sample is measured. Referenced to the known 2PA cross section of Rhodamine B (∼53 GM at 650 nm) listed in the literatures, each measurement is repeated multiple times and averaged to retrieve the NLO coefficients. , …”

“…Fluorophore 1 – 2 @PDMS films were prepared following the reported method . In details, SYLGARD 184 silicone elastomer (PDMS precursor) was purchased commercially, which was composed of base gum and curing agent.…”

“…Referenced to the known 2PA cross section of Rhodamine B (∼53 GM at 650 nm) listed in the literatures, each measurement is repeated multiple times and averaged to retrieve the NLO coefficients. 67,68 Details for Data Processing. The coefficient β can be obtained by curve fitting to the observed open aperture traces with the following eqs 1−5.…”

“…Fluorophore 1−2@PDMS films were prepared following the reported method. 68 In details, SYLGARD 184 silicone elastomer (PDMS precursor) was purchased commercially, which was composed of base gum and curing agent. Stoichiometric amounts of base gum (10 mL) and curing agent (1 mL) were mixed, and then certain amount of fluorophore 1−2 in dichloromethane (DCM) was added under stirring.…”

Nonlinear Characterization and Related Photophysics of Two-Photon Absorption

“…其中荧光量子产率 F 亦由单线态能级S 1 辐射跃迁返回基态S 0 ， 可认为与1PA荧光量子产率保持一 致；式中1/2的引入因为物质同时吸收两个光子，N为样品的荧光单元密度，L为样品厚度。K为无量 纲常数，与荧光收集效率、光束几何形状和自吸收修正系数有关；若实验中使用了相同的光学装置， 可认为K值相同。实际操作中，参比样品与待测样品的双光子吸收光谱和荧光发射光谱重合度越好， 测试结果越可靠 [19] 。2PA化合物如罗丹明6G、罗丹明B、荧光素、卟啉衍生物等的δ 2PA 参考值已被广 泛报道 [20][21][22] 。Xu和Webb等基于2PEF方法对罗丹明6G、荧光素等在690-960 nm波长范围内的δ 2PA 数 值进行了系统测定，其中罗丹明6G的甲醇溶液体系在700 nm处δ 2PA 参考值约为150 GM [20] 。同时对罗 丹明B、荧光素等在690-1050 nm波长范围内的δ 2PA 数值进行了详细考查，罗丹明B的δ 2PA 数值在691 nm 处为194 ± 50 GM，在840 nm处约为210 GM，测试使用溶剂为甲醇，激光脉宽为100飞秒 [23] 。因此分 别测试未知化合物和参比化合物的荧光积分强度，代入已知的参比双光子吸收截面δ r 、二者的量子 产率、仪器荧光收集效率φ等参数来间接计算待测化合物的δ s ，计算求得待测样品的δ s ：…”