Dechirping analysis and calibration strategies for broadband laser ranging*

The precise location of surfaces and ejected particulates is inferred through the fielding and analysis of broadband laser ranging. This developmental diagnostic complements its predecessor, photonic Doppler velocimetry, and is appropriate for surfaces moving many kilometers per second, including movement that is non-normal to the probe. Light from a pulsed femtoseconds laser is reflected from the target surface and mixed with light from a reference leg, which is then passed through dispersive fiber, resulting in chirped beat signals at the detector. Within the analysis, the dispersed laser pulses require temporal remapping due to the nonlinear optical dispersion of the fiber. Various approaches, including minimizing FFT peak widths and estimating phase, are discussed here, along with their respective merits. In addition, techniques for data calibration are presented, focusing on in-situ calibration for dynamic experiments and what to do when all else fails.