Observations of multipass transverse modes in an axially pumped solid-state laser with different fractionally degenerate resonator configurations

Abstract

We experimentally show, for the first time to our knowledge, that a diode-pumped Nd:YVO4 laser can operate with multipass transverse (MPT) modes that self-reproduce after several round trips in a plano-concave cavity that has fractionally degenerate resonator configurations when the pump beam waist is sufficiently smaller than that of the fundamental cavity mode. The MPT mode is found to exhibit multiple beam waists located at different positions and to experience a lower pumping threshold than the single-pass transverse mode. With off-axis pumping, the N-pass transverse mode forms a symmetric pattern for even N and an asymmetric pattern for odd N. This result can be explained as being due to the introduction of MPT modes but not to superposition of the standard cavity modes. (C) 2001 Optical Society of America.