Astigmatism compensation for waveguide inscription in optical fiber by femtosecond lasers

The cylindrical geometry of optical fibers produces an astigmatic distortion in a wavefront focused within it. In the case of femtosecond lasers, this produces a fluence loss that decreases its processing performance. In this work, the phase change produced by an astigmatic femtosecond laser beam (direct exposition to the) and a corrected beam (applying a simple adaptive optics process) is compared. The astigmatic correction decreases the modification threshold by approximately a magnitude order and changes the sign of the refractive index change at low pulse energies.