Stable intracavity doubling of orthogonal linearly polarized modes in diode-pumped Nd:YAG lasers

The stability of the output light from a diode-pumped intracavity frequency-doubled Nd:YAG laser was studied. An intracavity nonlinear crystal, such as Type II phase-matched potassium titanyl phosphate, was used for frequency doubling. The incident beam consisted of two orthogonal linearly polarized modes. When the polarization eigenvectors were parallel to the E and O axes of the crystal, a large amplitude fluctuation was observed; however, when the azimuthal angle between the polarization eigenvectors and the axis was 45 degrees , the light output was stabilized. The experimental results are explained by analyzing the coupling of the two orthogonal linearly polarized modes through a sum-frequency-generation process.