Using Optical Tweezers to Simultaneously Trap, Charge, and Measure the Charge of a Microparticle in Air

Area of Science:

• Atomic, Molecular and Optical Physics
• Nanotechnology and Nanoscale Science
• Physical Chemistry

Background:

• Optical tweezers are precise tools for measuring forces on micron-scale particles.
• Measuring particle electric charge is a key application, feasible in various environments.
• The influence of the trapping laser on particle charge is not fully understood.

Purpose of the Study:

• To investigate the electrical charging of micron-scale SiO2 spheres by the trapping laser in optical tweezers.
• To elucidate the underlying physical mechanism responsible for laser-induced particle charging.
• To develop and validate a model for this charging process.

Main Methods:

• Experimental setup utilizing optical tweezers to trap SiO2 spheres (∼1 μm) in air.
• Systematic measurement of particle charge influenced by the trapping laser.
• Development of a theoretical model based on a two-photon absorption process.

Main Results:

• The trapping laser itself was found to electrically charge the SiO2 spheres.
• Experimental data showed high fidelity with the proposed two-photon charging model.
• This mechanism explains the observed charging behavior under optical trapping.

Conclusions:

• The trapping laser in optical tweezers can induce electrical charging in dielectric microparticles.
• A two-photon process accurately describes the laser-induced charging mechanism.
• Understanding this effect is crucial for precise force measurements and particle manipulation.