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

Abstract

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.

Stabilizing Unstable Steady States Using Multiple Delay Feedback Control

“…Laser stabilization.-Since the first investigation of chaotic intensity fluctuations of frequency doubled Nd:YAG lasers by Baer [1] many attempts have been made to cope with this type of dynamical instability. Optical counter measures include adding a quarter-wave plate to the cavity [17,18], rotating the KTP crystal [19,20], or using an L-shaped cavity [21]. On the other hand, many authors investigated the chaotic dynamics of frequency doubled Nd:YAG lasers and applied different chaos control methods.…”

Hopf bifurcation in parallel polarized Nd:YAG laser

“…Studies by Oka and Kubota have shown that the laser dynamics is strongly influenced by the polarizations of the cavity modes [3]. This dependence is due to the fact that the amount of green light produced by sum frequency generation depends on whether the contributing fundamental modes are polarized parallel or orthogonal to each other.…”

Polarization dynamics of intracavity frequency-doubled Nd:YAG laser

“…Two types of phase matching of light waves in nonlinear crystals are used for intracavity frequency doubling: type I includes frequency mixing of laser modes of one polarization, whereas type II mixes the laser modes of the orthogonal polarizations. In intracavity frequency doubling lasers with type II phase matching stabilization is performed, e.g., by adding a quarter-wave plate [5] or two crossed nonlinear crystals [6] to the laser cavity. With type I phase matching, the laser usually oscillates in only one polarization mode, and the instability of the output appears due to the coupling of longitudinal modes [7].…”

“…4. Reduction of the spatial inhomogeneities of the gain, e.g., by using a quarter-wave plate [5], or ring lasers, since it reduces the amplitude of low-frequency relaxation oscillations.…”