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BP: Fachverband Biologische Physik

BP 26: Poster Session II

BP 26.21: Poster

Donnerstag, 29. März 2007, 17:00–19:30, Poster B

2c2p excitation and its applications in fluorescence microscopy — •Stefan Quentmeier, Raluca Aura Niesner, and Karl-Heinz Gericke — TU-Braunschweig

We report observation of two-color-two-photon (2c2p) excitation of p-Terphenyl and Furan-2 upon excitation with 400 and 800 nm using the SHG and fundamental wave of a modelocked Ti:Sa femto second laser. This excitation is energetically equivalent to a one photon excitation employing 266 nm light. The fluorescence signal is only visible when both wavelengths are spatially and temporal overlapping. Variation of the delay of the 800 nm puls renderes an cross correlation curve which is in good agreement with the pulse width of our laser. In addition, the fluorescence signal is linear dependent on the intensity of each of the two colors but quadratically on the total incident illumination power of both colors. As background signal we observe one-color-two photon-excitation from the 400 nm light. This background signal can easily be reduced be adjusting the power of the blue light. This results in an increased signal to noise ratio as the 2c2p signal decreases linearly while the 1c2p signal decreases with quadratic dependence on the 400 nm beam. Hence in fluorescence microscopy the use of a combination of intense IR and low intensity blue light as a substitute for UV light for excitation can have numerous advantages. Furthermore the possibility of manipulating the polarisations of both absorbed photons independently offers information about different transition symmetries and, therefore, allows to distinguish between two molecules absorbing at the same wavelength.