Nd:YAG ring laser with 213 W linearly polarized fundamental mode output power

We present a high power fundamental mode ring oscillator with four longitudinally diode-pumped laser rods and effective birefringence compensation as a laser source for the next generation of gravitational wave detection. With this setup a linearly polarized output power of 213 W in a nearly diffraction limited beam with an M2 value of 1.15 was demonstrated.