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.

中文翻译：

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用于快速测定简并双光子吸收光谱的色散白光连续单 Z 扫描

我们提出了一种实验技术，通过使用空心光纤产生的高光谱辐照度白光连续谱 (WLC) 执行单次 Z 扫描来确定简并双光子吸收 (2PA) 光谱。中空纤维充满压力为 0.6 bar 的氩气 (Ar)，并用 500 mJ、30 fs 和 800 nm 的脉冲进行泵浦。600-950 nm 范围内带宽为 350 nm 的宽带 WLC 脉冲被压缩至低于 8 fs 的脉冲。为了表征和解释从该方法获得的数据，首先分析了 WLC 的光谱、时间和空间特征。从压缩机中出现的 WLC 使用棱镜对进行分散，然后通过柱面透镜聚焦到样品中。由于不同的光谱成分在空间上是分离的，因此光束横截面中样品的任何部分都受到几乎单一波长脉冲的照射，导致仅发生简并 2PA 过程。然后，当样品通过电动平移台沿光束方向移动时，通过电荷耦合器件（CCD）线阵相机测量非线性透射率作为样品位置的函数。通过这种方式，可以测量 WLC 光谱范围内不同波长的 Z 扫描，因此可以通过使用色散 WLC 执行单次扫描来获得波长分辨简并 2PA 光谱。该方法在良好表征的染料罗丹明 B 上进行了验证，并与文献中的数据得出了合理的一致性。我们使用此方法确定了一些为基于 3D 微结构的双光子聚合 (2PP) 开发的双光子引发剂 (2PI) 的 2PA 光谱。