A tunable line optical tweezers instrument with nanometer spatial resolution.

Area of Science:

• Physics
• Colloidal Science
• Optical Physics

Background:

• Measuring interactions between colloidal particles is crucial for understanding material properties.
• Traditional optical tweezers have limitations in controlling trapping potentials and measuring precise particle separations.

Purpose of the Study:

• To develop a simple yet versatile optical tweezers instrument for accurate measurement of pair interactions between colloidal particles.
• To demonstrate precise control over the trapping potential landscape.
• To enable high-resolution measurement of particle separation, including out-of-plane motion.

Main Methods:

• Utilized a scanning-line optical tweezers system integrating a resonant scanning mirror and an acousto-optic modulator.
• Programmed the one-dimensional intensity profile and trapping potential energy landscape.
• Engineered one-dimensional harmonic traps with adjustable spring constants.
• Developed a method to extract out-of-plane motion from relative particle brightness.

Main Results:

• Successfully created and measured a family of one-dimensional harmonic traps with controlled spring constants.
• Achieved a balance of forces to create a flat potential near particle contact, facilitating interaction measurements.
• Resolved relative particle separation with approximately 1 nm precision by analyzing out-of-plane motion.

Conclusions:

• The developed scanning-line optical tweezers offer a simple and effective platform for studying colloidal particle interactions.
• Precise control over trapping potentials and high-resolution separation measurements are demonstrated.
• The instrument advances the capability for detailed investigation of inter-particle forces in colloidal systems.