title: Axial resolution limit of a fiber-optic fluorescence probe.
abstract: We examine the limit of spatial resolution achievable when a sine optical fiber is used for excitation and collection of fluorescence from a bulk specimen. We calculate the probability of detecting a fluorescent particle as a function of its position relative to the fiber face, using excitation wavelength lambda, radius a, numerical aperture N.A., and the particle's fluorescence and absorbance spectra. Treating Rhodamine B as a model fluorescent analyte and using appropriate fiber parameters, we show that the maximum axial resolution (defined as the axial distance in a homogenous solution within which 50% of the detected signal originates) achievable is approximately 10 microm. We experimentally measured the axial resolution for a 500-microM aqueous solution of Rhodamine B with lambda = 543 nm, a = 1.31 microm, and a N.A. of 0.16 and found good qualitative agreement with the calculation.
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India.
authors.forename: J
authors.initials: J
authors.lastname: Balaji
authors.forename: Kanchan
authors.initials: K
authors.lastname: Garai
authors.forename: Subhasis
authors.initials: S
authors.lastname: Chakrabarti
authors.forename: Sudipta
authors.initials: S
authors.lastname: Maiti