We report on a compact optical frequency standard (OFS) based on a Telecom laser diode operating at ~ 1542 nm, frequency stabilized to a narrow iodine transition located in the green range of the visible domain (~514 nm), after a highly efficient frequency tripling process. We use two cascaded waveguide Lithium Niobate nonlinear crystals for the third harmonic generation process (THG), resulting in a harmonic power of 300 mW in the green range (@ 3) using 800 mW of infrared power (@ ). This result corresponds to an optical conversion efficiency P/P > 36 % which is -to our knowledge-the best result ever reported for a third harmonic process in continuous wave regime (CW). This process uses only 20 W of total consumption power, which can be drastically reduced, knowing that less than 10% of that green power level is needed for the iodine Doppler free spectroscopy, and consequently for the frequency stabilization purpose. We have already demonstrated a frequency stability of 2.9 x10 -14  -1/2 conferred to a laser diode operating at ~ 1542 nm, using the a1 hyperfine component of the R34 [44-0] located at ~ 514 nm. This corresponds to an amplitude spectral density of the residual frequency fluctuations < 10 Hz/√Hz. We plan to extend this approach to set up a new OFS by using a narrow linewidth fiber-laser emitting at ~ 1597 nm, which will be used for the phase-locking of a 1064 nm laser. Thus, this OFS, compact and mainly fibered, will perform the same role as that of a rigid optical cavity, widely used to stabilize 1064 nm lasers, involved in various terrestrial applications or space missions. The compact design of the whole setup will make it easily transportable to different sites and could be readily used as an ultra-stable frequency reference.

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