Biomedical applications involving multiphoton probes

Many techniques in biological and clinical science use multiphoton absorbers for fluorescence. The applications include medical imaging for living cells, diagnostic techniques for disease and spectroscopy. The intrinsic value of the multiphoton absorber coefficients is therefore of the utmost importance. Additionally, the laser intensity at which the absorber saturates can determine which absorber, dye or protein is useful for a particular application. Yet, experimental methods for determining the optical coefficients often yield different results. We describe several common methods of 2PA measurements and describe their features. As an example of the importance of applying the correct analysis to measurements, we fit experimental data and obtain values for multiphoton absorbers and accurately obtain their intrinsic values. Finally, we present the optical properties of several multiphoton materials used in biology.