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Performing label free coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) in endoscope imaging is a challenge, with huge potential clinical benefit. To date, this goal has remained inaccessible because of the inherent coherent Raman noise that is generated in the fiber itself. By developing double-clad hollow core photonic crystal fiber, we demonstrate coherent anti-Stokes Raman scattering and stimulated Raman scattering in an 'endoscope-like' scheme. Both the excitation beams and the collected CARS and SRS signals travel through the same fiber. No CARS and SRS signals are generated within the hollow core fiber even for temporally overlapping pump and Stokes beams, leading to excellent image quality. The CARS and SRS signals generated in the sample are coupled back into a high numerical aperture multimode cladding surrounding the central photonic crystal cladding. We demonstrate this scheme by imaging molecular vibrational bonds of organic crystal deposited on a glass surface.

Thin nanostructured metal films allow to control radiative and non-radiative losses of surface plasmon polariton modes without changing their group velocities. This effect is studied in plasmonic waveguides made of thin gold films drilled with very narrow slits and deposited on a GaAs substrate. The analysis is supported by high-resolution angle-resolved transmission measurements and rigorous electromagnetic calculations. We show that the excitation of air/gold and gold/GaAs surface waves leads to Fano-type resonances with specific light localization into the slits. As a result, gold/GaAs surface waves induce a modulation of radiative and non-radiative losses of air/gold surface waves. The minimum and maximum of the Fano-type resonance introduce two propagation regimes. In the radiative propagation regime, the losses due to the absorption are negligible, whereas an efficient inhibition of free-space coupling is demonstrated in low-loss propagation regime.