Optical Tweezers
LASER TRAPPING — 2018 NOBEL PRIZE IN PHYSICS
Focused laser beams create a harmonic potential well U = ½k·r². Particles with refractive index greater than the medium are drawn toward the intensity maximum by the gradient force. Thermal fluctuations (Brownian motion) kick particles with energy ~kT, setting an escape probability ∝ exp(−U/kT). Click to move the trap. Arthur Ashkin won the 2018 Nobel for this invention.