  The interferometric signals produced in conventional dual-comb laser ranging
require femtosecond lasers with long-term f_CEO stability, and are limited to
an upper sampling rate by radio-frequency aliasing considerations. By using
cross-polarized dual combs and two-photon detection we demonstrate
carrier-phase-insensitive cross-correlations at sampling rates of up to 12x the
conventional dual-comb aliasing limit, recording these in a digitizer-based
acquisition system to implement ranging with sub-100-nm precision. We then
extend this concept to show how the high data burden of conventional dual-comb
acquisition can be eliminated by using a simple microcontroller as a
ns-precision stopwatch to record the time intervals separating the two-photon
cross-correlation pulses, providing real-time and continuous LiDAR-like
distance metrology capable of sub-100 nm precision and dynamic acquisition for
unlimited periods.
