A systematic error of Michelson’s type lambdameters

2014 We describe here a systematic error that appears in Michelson’s type lambdameters when the measured laser is tuned during the measurement. Revue Phys. Appl. 21 (1986) 463-465 AOÛT 1986, Classification Physics Abstracts 07 . 60L 07 . 65 Tome 21 No 8 AOUT 1986 We want to describe here a systematic error of a certain type of laser lambdameters which appears when the wavelength of the laser to be measured is swept during the measurement These lambdameters are Michelson’s type interferometers, with a moving mirror which is usually made of a cube corner (C.C.) [1, 2]. The interferometer is illuminated by the counter-propagating beams of a reference laser (wavenumber Gr) and the laser to be measured (wavenumber a). To make a measurement, the C.C. is displaced, the optical path difference varying from li to 12 (we neglect here all the dispersion effects). The number of fringes observed on the reference laser is and on the laser to be measured The ratio of the wavenumbers is deduced from the ratio of the number of fringes and the measured value u. of the wavenumber Q of the unknown laser is (various tricks can be used in order to measure the fractional part of N and Nr). I£ now, the laser wavenumber Q is swept during the measurement, then equation (2) becomes where tl and t2 are the initial and final time of the measurement and 7 = ((1(t2) + (1(tl))/2, T = (12 + il)/2. Therefore we see that application of equation (3) gives a measured value which differs from the « average wavenumber » Q by a corrective term. As T can be equal to several times (12 /1)’ this term may be equal to a few times the range Au over which the laser wavenumber is swept during the measurement (i.e. between tl and t2), and therefore the measured value Qm may be outside the interval [G(t 1); U(t2)]. This systematic error is easy to detect because it depends on the relative sign of T and (12 11); it changes sign with the sign of the mean path difference and with the direction of motion-of the moving mirror. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:01986002108046300