Solvent Artifact in Nonlinear Absorption Measurement by the Open-Aperture Z-Scan Method
Apparent nonlinear absorption signal that can be an artifact in the two-photon absorption measurements by the open-aperture Z-scan method is demonstrated. Through the thick sample of neat solvents, sudden depression in the transmittance against the change of optical intensity of the incident laser beam was observed. The diffraction pattern and spectral measurement of the transmitted laser beam show that the depression arises from nonlinear Raman scattering process. The sudden change versus optical intensity with a certain threshold leads a deformed open-aperture Z-scan trace, clearly different from the normal shape of the traces by two-photon absorption. The obtained thresholds for two common solvents suggest that the Raman effect can affect the measurements under the thin sample condition.
Keywords: nonlinear optics, nonlinear absorption, open-aperture Z-scan, nonlinear Raman scattering, methodology,