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Optical Tweezers: Radial-vs-Axial Trap Stiffness

Interactive 2D optical tweezers simulator: a focused Gaussian beam traps a dielectric bead in a full transverse-plus-axial force field. Watch the bead's 2D Brownian jitter reveal why a real single-beam trap is always far stiffer sideways than along the beam, and tune numerical aperture, power and bead size to see the trap stiffen, shift, or fail.

Physics & Mechanics2DAdvanced60 FPS📱 Mobile-adapted⇄ 3D version

A real single-beam optical trap is never equally stiff in every direction: the same forward-pushing scattering force that shifts the axial equilibrium downstream also weakens the axial spring, while nothing opposes the sideways pull toward the beam axis. This 2D simulator computes the full transverse-plus-axial optical force field from the beam's own waist and Rayleigh range — extending the axial-only slice of the 3D version into a genuine two-dimensional (x, z) trap map — so you can watch a Brownian bead's cloud of thermal fluctuations come out visibly tighter sideways than along the beam, and see the numerically measured stiffness ratio k_x/k_z respond to numerical aperture, laser power and bead size exactly as a real calibrated trap would.

⚙ Under the hood

Interactive 2D optical tweezers simulator computing the full transverse-plus-axial force field of a focused Gaussian beam, not just the on-axis slice: a dielectric bead undergoes 2D overdamped Langevin dynamics in the trap, and live finite-difference readouts of radial stiffness k_x versus axial stiffness k_z reveal why a real single-beam trap is always noticeably stiffer sideways than along the beam.

opticsoptical tweezersradiation pressurebiophysicslaser trappinggradient forcebrownian motion2D

2D · HTML5 Canvas 2D · 60 FPS target · runs fully client-side, no install