title: Fiber delivered probe for efficient CARS imaging of tissues.
abstract: We demonstrate a fiber-based probe for maximum collection of the coherent anti-Stokes Raman scattering (CARS) signal in biological tissues. We discuss the design challenges including capturing the backscattered forward generated CARS signal in the sample and the effects of fiber nonlinearities on the propagating pulses. Three different single mode fibers (fused silica fiber, photonic crystal fiber and double-clad photonic crystal fiber) were tested for the probe design. We investigated self-phase modulation, stimulated Raman scattering (SRS) and four-wave-mixing (FWM) generation in the fiber: nonlinear processes expected to occur in a two-beam excitation based probe. While SPM and SRS induced spectral broadening was negligible, a strong non phase-matched FWM contribution was found to be present in all the tested fibers for excitation conditions relevant to CARS microscopy of tissues. To spectrally suppress this strong contribution, the pro design incorporates separate fibers for excitation light delivery and for signal detection, in combination with dichroic optics. CARS images of the samples were recorded by collecting the back-scattered forward generated CARS signal in the sample through a multi-mode fiber. Different biological tissues were imaged ex vivo in order to assess the performance of our fiber-delivered probe for CARS imaging, a tool which we consider an important advance towards label-free, in vivo probing of superficial tissues.
authors.affiliation: Laser Microbeam and Medical Program (LAMMP), Beckman Institute and Medical Clinic, 1002 Health Sciences Road East, University of California, Irvine, 92612, USA.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Balu
authors.forename: Gangjun
authors.initials: G
authors.lastname: Liu
authors.forename: Zhongping
authors.initials: Z
authors.lastname: Chen
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Tromberg
authors.forename: Eric O
authors.initials: EO
authors.lastname: Potma
mesh_terms: D000818:Animals; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D051379:Mice; D009928:Organ Specificity; D011817:Rabbits; D012542:Scattering, Radiation; D013059:Spectrum Analysis, Raman / Q000295:instrumentation*; D013997:Time Factors