Two particle tracking and detection in a single Gaussian beam optical trap.

Area of Science:

• Optical trapping
• Microfluidics
• Nanotechnology

Background:

• Accurate tracking of microbead positions is essential for understanding interactions in optical traps.
• Quadrant photodetector (QPD) based detection schemes are commonly used but can be influenced by detection geometry.

Purpose of the Study:

• To investigate the influence of detection schemes on the accuracy of microbead position determination in an optical trap.
• To identify the optimal detection method for reliable tracking of axially trapped microbeads.

Main Methods:

• Axial trapping of two microbeads in a single-beam Gaussian optical trap.
• Power spectral density analysis of intensity fluctuations recorded by a QPD.
• Utilizing forward- and backscattering detection schemes with single and dual laser wavelengths.
• Employing computer simulations and Mie scattering analysis.

Main Results:

• The corner frequency, derived from power spectral density analysis, is dependent on the chosen detection scheme.
• Backscattering detection accurately reflects the position of the first microbead in the beam path.
• Forward scattering detection yields position information from both beads, with a bias towards the first bead, due to significant interference.

Conclusions:

• Backscattering detection is imperative for accurately tracking the true displacements of axially trapped microbeads.
• Understanding scattering interference is crucial for resolving individual bead positions in forward scattering detection.
• Accurate bead tracking via backscattering enables further studies on light-mediated interbead interactions.