Preparation of Long Coherence-Length Second Harmonic-Generating Optical Fibers using Modelocked Pulses.

We have prepared an optical fiber that produces efficient (0.24%) second-harmonic conversion using modelocked 1.064micron laser pulses along with a harmonic seeding beam. The effective coherence length increased to 35 cm as compared to only a few cm in fibers prepared with modelocked, Q-switched pulses. We show that the input bandwidth of the pump pulse imposes a fundamental limit on the effective coherence length and that this length can be severely reduced by competing nonlinear effects.