Linking the 474 THz HeNe/I2 standard to the 445 THz single Sr+ trapped ion standard: heterodyne frequency measurements using an OsO4 stabilized 29 THz laser system. - Alan A. Madej; Klaus J. Siemsen; L. Marmet; John E. Bernard; Ouali Acef (IEEE Trans. Instrum. Meas., 1999)