Ajami Aliasghar, Husinsky Wolfgang, Ovsianikov Aleksandr, Liska Robert
1Faculty of Physics, Semnan University, P. O. Box 35195-363, Semnan, Iran.
2Institute of Applied Physics, TU Wien (Technische Universitat Wien), Wiedner Hauptstrasse. 8, 1060 Vienna, Austria.
Appl Phys B. 2018;124(7):142. doi: 10.1007/s00340-018-7011-0. Epub 2018 Jun 22.
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.
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白光连续谱（WLC）进行单次Z扫描来确定简并双光子吸收（2PA）光谱。空心光纤内充有压力为0.6巴的氩气（Ar），并用500毫焦、30飞秒和800纳米的脉冲进行泵浦。在600 - 950纳米范围内具有350纳米带宽的宽带WLC脉冲被压缩至8飞秒以下的脉冲。为了表征和解释通过该方法获得的数据，首先分析了WLC的光谱、时间和空间特性。从压缩器出射的WLC通过一对棱镜进行色散，然后由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，光束横截面内样品的任何部分几乎都被单一波长的脉冲照射，从而仅产生简并双光子吸收过程。然后，当样品通过电动平移台沿光束方向移动时，由电荷耦合器件（CCD）线相机测量非线性透过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，从而通过使用色散WLC进行单次扫描获得波长分辨的简并2PA光谱。该方法在特性明确的染料罗丹明B上得到了验证，并且与文献中的数据取得了合理的一致性。我们使用该方法确定了一些为基于双光子聚合（2PP）的3D微结构开发的双光子引发剂（2PI）的2PA光谱。
