  We report on telecom laser frequency stabilization to narrow iodine hyperfine
line in the green range of the optical domain, after a frequency tripling
process using two nonlinear PPLN crystals. We have generated up to 300 mW
optical power in the green (P3w), from 800 mW of infrared power (Pw). This
result corresponds to an optical conversion efficiency eta= P3w/Pw ~ 36 %. To
our knowledge, this is the best value ever demonstrated for a CW frequency
tripling process. We have used a narrow linewidth iodine hyperfine line
(component a1 of the 127I2 R 35 (44-0) line) to stabilize the IR laser yielding
to frequency stability of 4.8x10-14 t-1/2 with a minimum of 6x10-15 reached
after 50 s of integration time. The whole optical setup is very compact and
mostly optically fibered. This approach opens the way for efficient and elegant
architecture development for space applications as one of several potential
uses.
