Application Note: High-Precision Metrology

By IMRA America, Inc.

A number of non-contact techniques for metrology, ranging, and surface profiling have been developed over the years, including interferometry, moiré fringe topography, and timeof- flight (TOF) methods such as LIDAR. This type of technique is most valuable in the field of civil engineering, construction, surveying, & industrial plant maintenance, quality control, component identification, etc. Lasers have for many years provided a means for improved precision & accuracy in metrology applications. One commercially available method used today utilizes high-accuracy RF phase detection of a modulated laser beam reflected from a target. However, researchers at AIST Metrology Institute of Japan have recently demonstrated an improved method which uses a femtosecond, modelocked fiber laser (Femtolite C-15) to obtain unprecedented levels of accuracy over long distances.1 Performing measurements in the optical testing tunnel at AIST, an absolute accuracy of millimeters can be obtained for targets at a range of over 200 meters, with a position sensitivity of tens of microns.2