Trapping Micrometer-sized Silica Beads with Optical Tweezers

Optical tweezers are an optical instrument that use a high power, highly focused laser beam to hold and move small particles. Optical tweezers have been used in a variety of different applications, in the fields of biology and biophysics. In certain cases they are used to grab and hold viruses, bacteria, or molecules including DNA. This tweezer works based on light carrying momentum proportional to its energy and propagation direction. When the laser passes through the object it refracts and alters its momentum. The object undergoes a restoring force to conserve the total momentum which causes the object to be pushed to the center of the focused laser causing it to be trapped within the laser. We present the details of an optical tweezers set up that we designed and constructed in the lab. This set up was used for the study of the Brownian motion of the micrometer-sized silica beads in a water medium. By tracking and recording the random motion of the beads within the medium we determined the viscosity and resistive force of the medium. Once the bead was successfully trapped, the strength of the trapping force of the optical tweezers was determined at varying laser intensities.

Optics

2023-2024

Stevens Point, WI