POLARIZATION-DEPENDENT SPECTRAL MODULATION IN FEMTOSECOND TI-SAPPHIRELASERS

We investigate spectral modulation in self-mode-locked femtosecond Ti: sapphire lasers. The spectra of the laser output and of the light refl ected from intracavity surfaces can exhibit a periodic modulation due to the laser rod acting as an intracavity birefringent filter. These s pectral features vary greatly between the two orthogonally polarized c omponents of the laser beam, The free spectral range and depth of the observed modulation depend on the crystal length and cavity alignment respectively. The qualitative features of the observed spectra can be explained using a simple model of the coupling between polarization st ates of the laser due to the birefringence of the laser rod. (C) 1998 Elsevier Science B.V.