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A. Ajami, W. Husinsky, A. Ovsianikov, R. Liska:
"Dispersive white light continuum single Z-scan for rapid determination of degenerate two-photon absorption spectra";
Applied Physics B - Lasers and Optics, 124 (7) (2018), S. 14201 - 14210.

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.