A mode-hop-free tunable single-longitudinal-mode Nd:YVO 4 laser with 25W of power at 1064nm

Abstract

It is well known that intra-cavity second-harmonic generation (SHG) suppresses mode hopping in solid-state resonators producing single-longitudinal-mode (SLM) output at the second-harmonic frequency (SHF). A simple extension of this concept is to suppress mode hopping in a resonator producing SLM output at the fundamental frequency (through an output-coupling mirror) by inserting an intra-cavity SHG crystal that converts a fraction of the intra-cavity power to the SHF. The beam at the SHF can either be dumped or is available as a second output beam. When combined with a PZT-actuated mirror, it is possible to continuously tune the frequency of the fundamental beam through a significant fraction of the gain bandwidth without mode hopping. SHG also suppresses mode hopping during warm up and during pumppower changes. These features were demonstrated in a unidirectional Nd:YVO₄ ring resonator producing an output beam greater than 25W at 1064nm while generating a few Watts at the SHF of 532nm. Mode hopping is substantially reduced during warm up and mode-hop-free operation can be sustained over many hours. Frequency tuning over several GHz was demonstrated and larger tuning ranges are possible. The PZT-actuated mirror can be used to eliminate frequency drift, to stabilize the output to a frequency standard (such as an atomic-absorption line), or to mitigate cavitylength changes due to acoustic noise.