title: Potential of multi-photon upconversion emissions for fluorescence diffuse optical imaging.
abstract: The spatial resolution of fluorescence molecular imaging is a critical issue for the success of the technique in biomedical applications. One important method for increasing the imaging resolution is to utilize multi-photon emissions. In this study, we thoroughly investigate the potential of the multi-photon upconversion emissions from rare-earth-doped upconverting nanoparticles for the improvement in spatial resolution of diffuse optical imaging. It is found that the imaging resolution is increased by a factor of 1.45 through employing two-photon upconversion emission compared with using the linear emission, and can be further elevated by a factor of 1.23 by using three-photon upconversion emission. In addition, we demonstrate that the pulsed excitation approach holds the promise of overcoming the low quantum yield associated with the high-order upconversion emissions.
authors.forename: Haichun
authors.initials: H
authors.lastname: Liu
authors.forename: Can T
authors.initials: CT
authors.lastname: Xu
authors.forename: Stefan
authors.initials: S
authors.lastname: Andersson-Engels