Short and long term frequency stability of linear monolithic intra-cavity frequency-doubled solid-state laser

Abstract

Single longitudinal mode visible DPSS are more and more used in devices where performance can be affected by short term (minutes) frequency drifts and hops. Long exposure holography and Raman spectrometry are applications requiring high frequency stability. Resonant external cavity frequency doubling (to generate CW deep UV) and pumping doubly resonant OPOs may be even more demanding applications in terms of frequency stability. Mechanical vibrations and thermal fluctuations are usual sources of short term frequency variations or instabilities. Monolithic ring cavities (such as NPRO) are known to solve this problem but they are quite expensive to manufacture. We will show that much simpler linear monolithic cavities used in our standard product line (SLIM-532, SLIM-550, SLIM-561 and SLIM-660) present best of class frequency stabilities compatible with the most demanding applications. Frequency tuning capabilities will be discussed and could be used in an active stabilization of the laser. Some applications can benefit from long term wavelength stability as well. Raman spectra can be monitored without control of the pump wavelength if the long term stability is good. In addition, narrow filters can be used to measure small Stokes shifts. We are monitoring several monolithic laser sources. After more than 6000 hours of operations, the wavelength shift is within 1 pm. The laser source has been restarted more than 1000 times without any change of the operating wavelength. Finally, thermal cycles do not impact the wavelength. In conclusion, we demonstrate that monolithic linear cavities are best suited for all applications requiring wavelength stability.