Propagation of femtosecond laser pulses through metal-coated tapered fibre probe

Using the three-dimensional finite difference time domain (3D-FDTD) method, we calculate light field in metal-coated optical fiber probes with different taper angles and different lengths under illumination of femtosecond laser pulses. The transmission of temporal fields of the laser pulses propagating in the probes and the properties of their frequency spectrum and phases are studied. The influences of the taper angle and the length of the probe on these properties are analyzed. The calculation results show that the structure of probe leads to the broadening, amplitude oscillation and the spectrum splitting of the laser pulses. With the analysis of the spectrum and the phase variation, we give a preliminary explanation to the phenomena of the pulse broadening and the periodic variation of the pulse amplitude with time.