title: Back-scattered detection yields viable signals in many conditions.
abstract: Precision position-sensing is required for many microscopy techniques. One promising method, back-scattered detection (BSD), is incredibly sensitive, allowing for position measurements at the level of tens of picometers in three dimensions. In BSD the position of a micron-sized bead is measured by back-scattering a focused laser beam off the bead and imaging the resulting interference pattern onto a detector. Since the detection system geometry is confined to one side of the objective, the technique is compatible with platforms that have restricted optical access (e.g. magnetic tweezers, atomic force microscopy, and microfluidics). However, general adoption of BSD may be limited according to a recent theory [Volpe et al., J. Appl. Phys. 102, 084701, 2007] that predicts diminished signals under certain conditions. We directly measured the BSD response while varying the experimental conditions, including bead radius, numerical aperture, and relative index. Contrary to the proposed theory, we find that all experimental conditions tested produced a viable signal for atomic-scale measurements.
authors.affiliation: Department of Physics, Amherst College, Amherst, Massachusetts 01002, USA.
authors.forename: Frederick B
authors.initials: FB
authors.lastname: Shipley
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Carter
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation*; D007368:Interferometry / Q000295:instrumentation*; D007834:Lasers; D008853:Microscopy / Q000295:instrumentation*; D008863:Microspheres; D010783:Photometry / Q000295:instrumentation*