Randomizing phase to remove acousto-optic device wiggle errors for high-resolution optical tweezers.

Acousto-optic (AO) devices have been used extensively in optical tweezers because of their flexibility and speed; however, these devices have trap positioning inaccuracies that limit their usefulness, especially for high-resolution applications. We show that these inaccuracies are due to interference patterns within the AO device sound fields. We have devised a method that removes these inaccuracies by reducing the coherence of the sound fields by directly controlling and randomizing the phase of the radio frequency voltage input signal. We demonstrate that the trapping inaccuracies are eliminated, for both constant trap position and force-ramp measurements, and that no additional noise is added. We show that this random phase method is applicable to both acousto-optic modulator and deflector type devices and can be easily integrated via software upgrade into existing instruments.