Two-photon dual-comb LiDAR imaging.

Conventional LiDAR uses time-of-flight data from laser pulses scanned across a scene to provide accurate multi-meter-scale three-dimensional models at cm precision, limited by the tens-of-picoseconds precision of time-tagging electronics. Here, by using two-photon dual-comb ranging, we introduce an analog of LiDAR imaging using the time-of-flight of sub-picosecond laser pulses to render cm-scale point-cloud datasets with µm precision. Using only free-running femtosecond lasers, the technique combines absolute accuracy with near-interferometric precision, is applicable to discontinuous surfaces with poor optical quality, and provides a stand-off range exceeding that of typical non-contact optical surface metrologies. We demonstrate imaging of an aluminum test object and assess its accuracy by comparing our results with those from a touch-probe coordinate measurement machine. At a stand-off distance of 40 cm, we obtain ranging accuracies of 9 µm-38 µm, and precisions averaging to <3 µm after 250 ms.