A 0.4-mm-diameter probe for nonlinear optical imaging

A miniaturized probe that possesses a diameter of 0.4 mm is developed for two-photon-excited fluorescence imaging. The miniaturized probe was manufactured by the collapse of air holes and the formation of a lens on the tip of a double-clad photonic crystal fiber (DCPCF) using electric arc discharging from a conventional fusion splicer. As a result, a femtosecond pulsed laser beam delivered by the DCPCF can be directly focused on a sample for two-photon fluorescence imaging. The numerical aperture of the lensed DCPCF is 0.12. The corresponding focal spot size is 6 µm, which is close to the diffraction limit. This 0.4-mm-diamter probe can provide clear two-photon-excited fluorescence images of 10-µm-diameter fluorescent microspheres.