COMPARISON OF 2 WAVELENGTH REFERENCE LASER SYSTEMS AT LAMBDA-APPROXIMATE-TO-515-NM, STABILIZED BY DIFFERENT METHODS

The results of a comparison of two of the BIPM iodine-stabilized Ar+ l aser systems at lambda approximate to 515 nm are presented. One of the se laser systems uses the traditional third-harmonic locking technique while the other is realized using high-frequency modulation technique s. The frequency stability found in terms of the relative Allan standa rd deviation was 1,3 x 10(-12) tau(-1/2) for tau < 100 s, with a minim um of 1,5 x 10(-13) at about 100 s. This limit is believed to be set b y imperfections in the servo electronics for the laser using the third harmonic technique. The frequency difference between the two lasers w as measured for the a(3) component of the P(13) 43-0 transition over a period of twelve days. The mean frequency difference was found to be 0,1 kHz with a sample standard deviation of 1 kHz. The influence on th e laser frequency of the modulation index, iodine pressure and laser p ower are discussed.