The stability of a diode pumped Nd:YAG laser with intracavity KTP in an L-shaped cavity is studied. The mirror which connects the two cavity arms is a dielectric which also acts as a partial polarizer. This design provides a high level of stability for the total output power, despite the instability of the separate modes: separate modes are chaotic with large amplitude noise while the total output displays reduced noise below 1&percent; rms. A model based on the Jones matrices is studied numerically. It shows antiphase and clustering, in excellent qualitative agreement with the experimental data. ©1997 American Institute of Physics.