International comparison of He-Ne lasers stabilized with I-127(2) at lambda approximate to 633 nm - Comparison of the fifth- and third-harmonic locking techniques

An international comparison of I-127(2)-stabilized 633 nm He-Ne lasers lock ed either by the fifth- or the third-harmonic technique was carried out at the Finnish Centre for Metrology and Accreditation (MIKES) in September 199 8, The participating laboratories were the MIKES; the Metrology Research In stitute, Helsinki University of Technology (HUT); the Chinese National Inst itute of Metrology (NIM); the Czech Metrological Institute (CMI); the D. I. Mendeleyev Institute for Metrology (VNITM); and the Bureau International d es Poids et Mesures (BIPM). Raw measured frequency differences between lase rs were in the following ranges: -5.2 kHz to +11.9 kHz and -5.8 kHz to +4.9 kHz for the third- and fifth-harmonic locking techniques, respectively. Th e frequency offsets between the third- and fifth-harmonic techniques for di fferent components (d to g) were in the range 26 kHz to 35 kHz. The relativ e frequency stability of lasers given by the Allan standard deviations reac hed 2.6 x 10(-13) for two lasers using the third harmonic and only 1 x 10(- 12) for the same lasers using the fifth harmonic for a 2000 s sampling time . This comparison is part of the ongoing laser comparison carried out under the auspices of the Consultative Committee for Length (CCL, formerly CCDM) of the Comite International des Poids et Mesures (CIPM); it is also a EURO MET project (No. 462).