title: Spatially localized ballistic two-photon excitation in scattering media.
abstract: We describe spatially localized two-photon excitation in scattering media. Using femtosecond pulses at 770 nm from a Ti: Sapphire laser, we were able to excite fluorophores in capillary tubes under up to 1.5 mm of 0.5% intralipid. Displacement of the laser beam relative to the embedded samples indicates that highly localized excitation was possible with two-photon excitation, whereas one-photon excitation resulted in loss of spatial resolution due to excitation by the diffusely scattered photons. These results indicate that two-photon excitation in the scattering solution is due only to the ballistic photons, a result confirmed by frequency-domain time-resolved measurements. Selective excitation of adjacent embedded samples was found possible for two but not one-photon excitation.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore 21201, USA.
authors.forename: H
authors.initials: H
authors.lastname: Szmacinski
authors.forename: I
authors.initials: I
authors.lastname: Gryczynski
authors.forename: J R
authors.initials: JR
authors.lastname: Lakowicz
mesh_terms: D005217:Fat Emulsions, Intravenous; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000032:analysis; D005470:Fluorometry / Q000295:instrumentation* / Q000379:methods*; D007834:Lasers; D009570:Nitriles / Q000032:analysis; D017785:Photons; D012235:Rhodamines / Q000032:analysis; D013267:Stilbenes / Q000032:analysis; D013343:Styrenes / Q000032:analysis; D013997:Time Factors
chemical_list: C116158:4-(dimethylamino)-4'-cyanostilbene; D005217:Fat Emulsions, Intravenous; D005456:Fluorescent Dyes; D009570:Nitriles; D012235:Rhodamines; D013267:Stilbenes; D013343:Styrenes