Accuracy and precision in broadband laser ranging

Broadband laser ranging uses spectral interferometry and a dispersive Fourier transform to perform high repetition rate position measurements of explosively-driven surfaces typically moving at several km/s. A broadband fiber laser and fiber interferometer record distance as a relative delay between short pulses, and the beat spectrum of the pulses is mapped into the time domain via long propagation in dispersive fiber. Optical amplification and a fast oscilloscope allow the dispersed spectrum to be recorded in real-time, often at measurement rates of 20-40 MHz. The third-order phase of the dispersive fiber causes distortions in mapping the spectrum into time that must be compensated for when analyzing the measured data. We characterize the accuracy and precision of BLR systems by performing a scan of static positions and comparing our single-shot measurements against position measurements from a commercial Michelson interferometer. We demonstrate a combination of hardware and data analysis that measures position to within 30 microns over a 27 cm range with very high precision.