Abstract
A simple common path interferometer is proposed to measure displacement of a specular object. The interferometer consists of a focusing lens, a beam splitter, a plane mirror and the specular object. Interference fringes obtained by the interferometer are straight lines with the equal interval if there is no aberration of the focusing lens. As both optical path in the interferometer are symmetrical, only effect of a coma aberration is contributed for the formation of the interference fringe, even if there are many aberration in the focusing lens. An interval of the interference fringe narrows in proportion to an absolute value of the displacement of the specular object. The displacement is obtained by analyzing the interval of the interference fringe. The experiments were carried out in order to confirm the validity of the proposed interferometer. When the displacement of 10nm amplitude was given at 1Hz, the displacement was detected by the proposed interferometer.
