= Single-beam gradient trapping experiment
In 1986, <Arthur Ashkin>, <Joseph Martin Dziedzic>, <John Ernst Bjorkholm> and <Steven Chu> used spatially filtered $514.5\,\mathrm{nm}$ argon <laser> light, a water-immersion objective of <numerical aperture> $1.25$, and a water-filled glass cell. An auxiliary beam loaded large glass beads; dispersed small particles entered by <Brownian motion>. A side <microscope> and $90^\circ$ <scattering of light> detector provided readout. Their Fig. 1 shows a $10\,\mathrm{\mu m}$ bead below the focus with about $100\,\mathrm{mW}$. On p. 290, silica size was inferred by scattering against a latex standard; translating the cell imposed fluid drag. These observations support single-beam confinement, while inferred size depends on the scattering model.<Observation of a single-beam gradient force optical trap for dielectric particles by Arthur Ashkin and others>[A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm and Steven Chu, Observation of a single-beam gradient force optical trap for dielectric particles, 1986, pp. 288–290, Figs. 1–2 and final experimental paragraphs]{ref}
A loading beam can help bring a bead into the capture region without supplying its subsequent confinement. Distinguish loading, holding and sensing when interpreting an apparatus drawing. The following <optical trap position readout> is a proposed calibration arrangement; its detector layout is not a reconstruction of this historical experiment.
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