IMAGE-CONTRAST ENHANCEMENT FOR 2-PHOTON FLUORESCENCE MICROSCOPY IN A TURBID MEDIUM

Image contrast enhancement is investigated for two-photon excitation f luorescence images of a microscopic sample that is buried underneath a turbid medium. The image contrast, which deteriorates rapidly with sa mple depth because of scattering loss, is enhanced by an increase in t he average excitation power of the focused Gaussian (the TEM,, mode) b eam according to a compensation relation that has been derived by use of a Monte Carlo analysis of the scattering problem. A correct increas e in the excitation power results in a detected fluorescence signal th at remains invariant with sample depth. The scheme is demonstrated on images of DAPI-stained nuclei cells viewed underneath a suspension of 0.105-mu m-diameter polystyrene spheres. (C) 1998 Optical Society of A merica.