Frequency doubling and stabilization of a Tm,Ho:YLF laser at 2051 nm to   a high finesse optical cavity
  Light from a Tm,Ho:YLF laser operating at 2051 nm is frequency doubled then coupled into a high Fabry-Perot cavity with manufacturer quoted finesse in excess of 300,000. The frequency of the laser is stabilized using the Pound-Drever-Hall (PDH) method. A two channel feedback circuit allows for laser frequency stabilization with a bandwidth of 2 MHz. This laser system has been used to drive the 6S1/2 to 5D3/2 transition in 138Ba+, where a 2 ms laser-ion coherence times has been observed, demonstrating a linewidth of less than 500 Hz. The intensity noise of this system is analyzed and found to be acceptable for several proposed experiments on a single trapped barium ion. 
Adam Kleczewski, Matthew Hoffman, Eric Magnuson, Boris Blinov, Norval   Fortson
physics.ins-det physics.atom-ph