📄 Showing the "Simple" version — "Advanced" is not ready yet. Add it to favorites to help prioritize it. Ask for the full read

A standard laser rangefinder works like a stopwatch on a 100-meter dash: it times how long light takes to run to the target and back. But such a stopwatch has a limit: it ticks in steps of tens of picoseconds (trillionths of a second). In that step, light travels about a centimeter, so finer details are invisible.

Instead of single pulses, the new method uses two combs of thousands of ultra-short flashes, emitted at slightly different frequencies. Their overlap acts like a gear train: a tiny difference in speed becomes a large, easy-to-measure shift. Thus, a coarse stopwatch turns into a microscope for time.

Tests on an aluminum part from a distance of 40 centimeters showed an error no greater than 38 micrometers, and after half a second of signal accumulation, the average scatter was just 1 micrometer. The result matched readings from a coordinate measuring machine that probes the surface mechanically.

Such a laser eye is useful where you cannot touch: inspecting parts on a conveyor, examining fragile museum exhibits, or scanning hot or radioactive objects. Light flies there, measures, and returns without leaving a trace.

Original abstract

as written by the authors arXiv:2603.12729

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 $$\mu$$m 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 other optical 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 $$\mu$$m - 38 $$\mu$$m, and precisions averaging to 1.0 $$\mu$$m after 500 ms.