Omnidirectional dual-femtosecond absolute ranging for high-precision multi-target coordinate measurement

Absolute ranging based on dual femtosecond lasers employing nonlinear asynchronous optical sampling is characterized by a wide measurement range, high precision, and fast measurement speed. In this work, we present an omnidirectional femtosecond absolute ranging system for high-precision multi-target coordinate measurement in large-scale applications. The system integrates a 2D universal-joint rotary axis with dual femtosecond laser absolute meters, using a standard sphere with 40 nm sphericity as a reflective reference and measurement origin to compensate for geometric errors. The optical probe rotates around the sphere, extending the angular measurement range while suppressing rotary-axis–induced geometric errors. A theoretical model quantifies the influence of geometric errors on measurement accuracy, and experiments validate system performance. The femtosecond laser achieves intrinsic distance precision within 5 µm, and multilateration-based coordinate measurement reaches sub-millimeter accuracy (<0.1 mm). These results demonstrate that the combination of a standard sphere and 2D universal joint effectively eliminates rotary-axis–induced geometric errors, providing a reliable solution for large-scale, high-precision multi-target coordinate measurement in industrial metrology.