Scatterometer-levitator for light-scattering measurements with full control on particle position and orientation

The optical properties of a sample are important in, e.g., astrophysics and space science. The samples can be unique or available in limited quantities, implying that sample preservation is important. Established single-particle light-scattering measurements involve attaching the sample to a holder or measuring a laminar flow of particles, neither of which allows for a controlled and nondestructive measurement. Acoustic levitation is a state-of-the-art approach applicable to scattering measurements. We present an instrument capable of performing a full 4π scattering measurement, i.e., a measurement from any direction on the full 4π solid angle. We measure scattering properties of millimeter-sized samples at any direction. This is enabled by introducing a novel non-contacting sample holder based on acoustic levitation, which allows a disturbance-free measurement of an orientation-controlled sample. The instrument is scalable and currently employs polarized visible light (400–700 nm). It also measures beam and sample stability as well as temperature and humidity, to ensure consistency of measurements. We demonstrate a measurement of a sample consisting of agglomerated 500-nm silica spheres. The upper left 2×2 submatrix of the Mueller scattering matrix is measured from the sample along the scattering angle.