Measuring the complete force field of an optical trap

Area of Science:

• Physics
• Biophysics
• Nanotechnology

Background:

• Precise force measurement at the molecular level is crucial for optical traps.
• The linear approximation of optical trap force fields is insufficient for high-force, low-intensity applications.
• Understanding nonlinear light-microsphere interactions is essential for advanced applications.

Purpose of the Study:

• To measure the full nonlinear force and displacement response of an optical trap in two dimensions.
• To investigate the dependence of trap stiffening on microsphere size.
• To compare the linear detection ranges for force and displacement.

Main Methods:

• Utilized a dual-beam optical trap setup.
• Employed back-focal-plane photodetection for precise measurements.
• Performed measurements across a range of microsphere sizes.

Main Results:

• Observed significant trap stiffening beyond the linear regime, dependent on microsphere size.
• Confirmed agreement with Mie theory calculations for nonlinear behavior.
• Found that the linear force detection range substantially exceeds the linear displacement detection range.

Conclusions:

• The study provides a comprehensive method for calibrating optical traps beyond the linear regime.
• Characterizing nonlinear optical trap responses is vital for accurate force measurements in demanding applications.
• The findings enhance the utility of optical traps for molecular-level force studies.