An optical trap uses the forces from a focused light field to confine or manipulate a small particle. In an overdamped one-dimensional model, a translating localized potential exerts and balances linear drag.
For a force profile supported on an interval of width , set . If a trap of speed overtakes an overdamped particle with , then and . These expressions follow by changing to the trap-frame coordinate, whose velocity is . Smooth zeroes of can prevent finite passage.
For a passing optical trap on a circle of circumference with nonoverlapping support, a particle that is stationary between encounters receives displacement in each encounter. The trap revolution frequency and particle revolution frequency obey . This corrects the naive independent-kick estimate when the particle motion changes the encounter rate.
A triangular localized potential energy has forces behind and ahead of the trap centre. With , and , its circular response is for . A trapped particle has for , interpreting the discontinuous force at the cusp by a sticking or rounded-well limit.
For a translating potential energy profile with equal values at the two ends and linear drag force , a finite passing trajectory satisfies . Equivalently, since , . Compact support of the force alone is insufficient. At high speed the displacement is .
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Optical tweezers are sophisticated scientific instruments that use highly focused laser beams to manipulate microscopic particles, such as biological cells, viruses, and even small beads or other nanoparticles. The principle behind optical tweezers is based on the interaction of light with matter, specifically the way that photons—particles of light—carry momentum. When a laser beam is focused to a fine point, it creates a gradient of light intensity.
Sample usages:
- quantum computing startup Atom Computing uses them to hold dozens of individual atoms midair separately, to later entangle their nuclei