TWO-WAVELENGTH INTERFEROMETRY WITH OPTICAL HETERODYNE PROCESS

The device comprises : a laser device (10, 20) for the frequency n1 (11) and the frequency n2 (21), each provided with a polarizing beam splitter (12, 22) for producing crossed polarized partial beams of frequency n1 (13, 14) and n2 (23, 24), respectively, with a modulator (18, 28) for shifting the frequency of each of the partial beams to the frequency f1 or f2, respectively, with a pair of deflecting mirrors (15, 17, 25, 27) and with a polarizing beam splitter (16, 26) for uniting (19, 29) the partial beams n1, n1+f1, n2, n2+f2; two photodetectors (35, 45) before each of which a polarizer (34, 44) is arranged; a Michelson interferometer; a non-polarizing beam splitter (30) for distributing each of the partial beams (19, 29) into a measurement light beam (32) or a reference light beam (33). The reference light beam is transmitted to the corresponding photodetector (35). The measurement light beam (32) is transmitted to the Michelson interferometer and then to the corresponding photodetector (45).The photodetector signals are modulated in function of the amplitude, and the phase difference between the two modulated signals is determined. This phase difference depends only on the position of the test object and the equivalent wavelenght of the difference, n1-n2. For stabilization or correction, the device can be executed in duplicate and one of the executions used as a reference. The corresponding process can be applied to determine positions or distances as the interval between two positions. Uncertainties can be eliminated by shifting the distance or changing the frequency with simultaneous integration of the phase difference over time. L'installation comprend: un laser (10, 20) pour la fréquence n1(11) et n2 (21); respectivement un diviseur de faisceau polarisant (21, 22) pour produire des faisceaux partiels polarisés et croisés de fréquence n1 (13, 14) et n2 (23, 24); un modulateur respectif (18, 28) pour décaler les faisceaux d'une fréquence f1 et f2 ; une paire respective de miroirs de déflection (15, 17; 25, 27) et un diviseur de faisceau polarisant respectif (16, 26) pour réunir (19, 29) les faisceaux n1, n1+f1, n2, n2+f2; deux photodétecteurs (35, 45) munis chacun d'un polariseur (34, 44); un interféromètre de Michelson; un diviseur de faisceau non-polarisant (30) pour répartir les faisceaux partiels (19, 29) en un faisceau de mesure (32) et un faisceau de référence. Le faisceau de référence (33) arrive sur le photodétecteur (35) qui lui est assign