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We present the results obtained with a compact heterodyne refractometer at 633 nm based on the measurement of the frequency of a laser diode locked to a Fabry Perot cavity, by comparison with a He-Ne laser. An agreement with Edlen's formulas has been obtained at the level of 4/spl times/10/sup -8/, limited by the accuracy of these formulas. The principle of this instrument is similar to the refractometer already developed in our laboratory and working at 780 nm (N. Khelifa et al, Appl. Opt., vol. 37, pp. 156-161, 1998). This apparatus may be also used as an air wavelength reference as described in ref. (R. Thibout et al, Eur. Phys. J. AP., vol. 16, pp. 239-245, 2001).

We report recent results obtained at the BNM-LPTF with the new frequency measurement chain based on a femtosecond laser. An I/sub 2/ stabilized Nd:YAG optical frequency standard, developed at the BNM-INM as a national standard for the "mise en pratique" of the definition of the meter has been measured for the first time.