Nanometer-resolution distance measurement with a noninterferometric method

We have developed a noninterferometric technique for high-resolution distance measurement (optical ranging). The technique utilizes the fact that the wavelength of a broadband cw laser can be changed by external feedback. By placing the ranging target near the focal point of a microscope objective, we can make the feedback from the target, hence the laser wavelength, sensitive to the target position. The target position is determined from the laser wavelength with great resolution. In our experiments a 20-nm resolution is obtained. The resolution is limited by the instrumental resolution and mechanical stability of the experimental setup.