title: Effect of excitation wavelength on penetration depth in nonlinear optical microscopy of turbid media.
abstract: We present a comparative study of two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) imaging in turbid media at 800- and 1300-nm excitation. The depth-dependent decay of TPEF and SHG signals in turbid tissue phantoms is used to estimate the impact of light scattering on excitation intensity at each wavelength. A 50 to 80% increase in scattering length is observed using 1300-nm excitation, while peak TPEF emission intensity is obtained 10 to 20 microm beneath the surface for both sources. The increased penetration depth at 1300 nm is confirmed by TPEF and SHG microscopy of tissue phantoms composed of gelatin/microspheres and 3-D organotypic collagen-fibroblast cultures, respectively. Our results establish the feasibility of 1.3-microm excitation in nonlinear optical microscopy.
authors.affiliation: University of California, Irvine, Beckman Laser Institute Laser Microbeam and Medical Program, Irvine, CA 92617, USA.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Balu
authors.forename: Tommaso
authors.initials: T
authors.lastname: Baldacchini
authors.forename: John
authors.initials: J
authors.lastname: Carter
authors.forename: Tatiana B
authors.initials: TB
authors.lastname: Krasieva
authors.forename: Ruben
authors.initials: R
authors.lastname: Zadoyan
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Tromberg
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation* / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods; D007259:Infrared Rays; D036641:Microscopy, Fluorescence, Multiphoton / Q000295:instrumentation* / Q000379:methods; D009391:Nephelometry and Turbidimetry / Q000295:instrumentation* / Q000379:methods; D017711:Nonlinear Dynamics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity