The BIPM laser standards at 633 nm and 532 nm simultaneously linked to the SI second using a femtosecond laser in an optical clock configuration.
Long Sheng MaLennart RobertssonSusanne PicardJean-Marie ChartierH. KarlssonE. PrietoRobert WindelerPublished in: IEEE Trans. Instrum. Meas. (2003)