High-accuracy reference standards for two-photon absorption in the 680-1050 nm wavelength range

Area of Science:

• Photophysics and Spectroscopy
• Organic Materials Science
• Nonlinear Optics

Background:

• Accurate measurement of two-photon absorption (2PA) is crucial for developing advanced optical materials.
• Existing methods often face challenges in precision due to experimental complexities and parameter variations.
• Organic fluorophores are key components in various photonic applications, necessitating precise characterization.

Purpose of the Study:

• To accurately determine the degenerate two-photon absorption (2PA) spectral shape and cross-section of organic fluorophores.
• To enhance the precision of 2PA measurements through rigorous experimental control and validation.
• To explore the application of these measurements as reference standards in nonlinear transmittance studies.

Main Methods:

• Femtosecond fluorescence excitation spectroscopy was employed in the 680-1050 nm wavelength range.
• Rigorous evaluation of the quadratic dependence of fluorescence signal on photon flux was performed.
• Independent experimental comparisons and meticulous assessment of excitation pulse shape, laser power, and sample geometry ensured accuracy.

Main Results:

• The relative 2PA spectral shape was obtained with an estimated accuracy of 5%.
• Absolute 2PA cross-sections were measured at selected wavelengths with an accuracy of 8%.
• Significant improvements in measurement accuracy were demonstrated through refined experimental protocols.

Conclusions:

• The study presents a highly accurate method for measuring degenerate two-photon absorption in organic fluorophores.
• The validated methodology allows for reliable characterization of 2PA properties, crucial for material development.
• The findings support the use of these characterized fluorophores as reliable reference standards in nonlinear optical measurements.