Multi-photon excitation imaging

Multi-photon excitation imaging of dynamic processes in living cells and tissues... 

The NIR femtosecond laser microscope realized higher order multi photon excitation for aromatic compounds interferometric autocorrelation detection of the fluorescence from the microcrystals of the aromatic molecules confirmed that their excited states were produced not via stepwise multiphoton absorption but by simultaneous absorption of several photons. The microscope enabled us to obtain three-dimensional multiphoton fluorescence images with higher spatial resolution than that limited by the diffraction theory for one-photon excitation. 

Masters BR, So PTC. Multi-photon excitation microscopy and confocal microscopy imaging of in vivo human skin a comparison. Microscopy and Microanalysis 1999, 5, 282-289. 

An additional class of nonlinear optical effects is that of multi-photon absorption processes. Using these process, one can create excited states (and, therefore, their associated physical and chemical properties) with a high degree of three-dimensional (3D) spatial confinement, at depth in absorbing media. There are potential applications of multi-photon absorbing materials in 3D fluorescence imaging, photodynamic therapy, nonlinear optical transmission and 3D microfabrication. 

The excitation of the surface plasmon effect also induces strongly enhanced fluorescence properties of gold nanoparticles due to the enhanconent in the radiative rate of the inter-band electronic transitions relative to that in bulk metals. Metal nanoparticles, especially gold nanorods exhibit enhanced two-photon luminescence (TPL) and multi-photon luminescoice (MPL) [7, 8]. Strongly-enhanced TPL has been observed from individual particles [9, 10] and particle solutions [11] under femtosecond NIR laser excitation. This observation raises the possibility of nonlinear optical imaging in the NIR region, where water and biomolecules have... 

In conclusion, this review illustrates the last decade (2001-2012) of research endeavour devoted to the sensitisation of lanthanide luminescence by a nonlinear two- (multi-) photon process. The motivation for this project is to combine the unique spectroscopic properties of lanthanide complexes (sharp transitions, long luminescence lifetime, environment sensitivity, circularly polarised luminescence, etc.) with the huge potentialities of the biphotonic excitation (NIR excitation, 3D resolution, etc.), in particular for bio-imaging applications. To that end, several scientific and instmmental breakthroughs have been performed almost simultaneously by several groups around the world ... 

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