FREQUENCY-MEASUREMENT OF I-2 LINES IN THE NIR USING CA AND CH4 OPTICAL FREQUENCY STANDARDS

Frequency measurements of three NIR I-2 lines have been carried out us ing difference-frequency mixing of the emission of CH4 and Ca frequenc y standards at 88 THz (or 3.4 mu m) and 456 THz (or 657 nm), respectiv ely. A power of approximate to 10 pW for the mixing product at 815 nm was obtained using a critically phase-matched KTP crystal and input po wers of the order of mW. The relative uncertainty of the measurement w as a few times 10(-11), limited by the frequency instability of the la ser source locked to I-2.