Extending tracking range through structured back focal plane interferometry

Abstract

Back Focal Plane interferometry (BFPI) is a widely used technique in particle tracking, providing high-speed, highresolution measurements. We present Structured Back Focal Plane Interferometry (SBFPI), a modification to BFPI utilizing structured beams and structured detectors [1]. Utilising Conical Wavefront Gaussian Beams and Annular Quadrant Photodetectors, SBFPI significantly increases tracking range while maintaining sensitivity and robustness to aberrations. We studied the variation in detection range and sensitivity over our parameters. A maximum increase in axial and lateral tracking range of 4.25-fold and 1.83-fold was found respectively, concomitant with sensitivity decreases of 53% and 61%. We also found parameter combinations with smaller range improvements but which retain sensitivity, in particular a 2.31 fold axial range increase with a 22.4% reduction in sensitivity, and these can be tuned to each experiment. We also studied the effect of aberrations on signal integrity. Keywords: Back Focal Plane Interferometry, Conical Wavefront, Gaussian Beam, Structured Light