Highly-efficient coupling of linearly- And radially-polarized femtosecond pulses in hollowcore photonic band-gap fibers

We demonstrate extremely efficient excitation of linearly-, radially-, and azimuthally-polarized modes in a hollow-core photonic bandgap fiber with femtosecond laser pulses. We achieve coupling efficiencies as high as 98% with linearly polarized input Gaussian beams and with highpower pulses we obtain peak intensities greater than 10¹⁴ W/cm² inside and transmitted through the fiber. With radially polarized pulses, we achieve 91% total transmission through the fiber while maintaining the polarization state. Alternatively with azimuthally-polarized pulses, the mode is degraded in the fiber, and the pure polarization state is not maintained.