Abstract
Distances to multiple targets are measured simultaneously using a single femtosecond pulse laser split through a diffractive optical element. Pulse arrival from each target is detected by means of balanced cross-correlation of second harmonics generated using a PPKTP crystal. Time-of-flight of each returning pulse is counted by dual-comb interferometry with 0.01 ps timing resolution at a 2 kHz update rate. This multi-target ranging capability is demonstrated by performing multi-degree of freedom (m-DOF) sensing of a rigid-body motion simulating a satellite operating in orbit. This method is applicable to diverse terrestrial and space applications requiring concurrent multiple distance measurements with high precision.
Highlights
Multi-degree of freedom sensing of an object in 3-D space is intended to identify its location as well as orientation simultaneously with respect to a unified reference frame
Various sensors of diverse principles are available for the purpose, among which gravity-referenced inclinometers or gyroscopes are preferably used for angle measurements, while laser interferometers or optical time-offlight instruments are well suited for distance measurements in free space
Parallel determination of absolute distances to multiple targets was demonstrated by time-offlight measurement using femtosecond light pulses
Summary
Multi-degree of freedom (multi-DOF) sensing of an object in 3-D space is intended to identify its location as well as orientation simultaneously with respect to a unified reference frame. Quite a few advanced interferometric techniques have been demonstrated; radio-frequency synthetic wavelength interferometry [14,15], pulse to pulse cross-correlation [16], dispersive interferometry [17], dual-comb multi-heterodyne interferometry [18,19,20], multi-wavelength interferometry [21,22,23] and time-of-flight measurement using nonlinear optical crosscorrelation [24,25] These techniques pursue the common aim to achieve the sub-wavelength precision in long-distance ranging by making use of unique time and/or frequency domain characteristics of femtosecond lasers. An uncertainty analysis is conducted to systematically validate the achieved measurement accuracy in consideration of major error sources involved in the measurement
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