Optimal condition for optical trapping of large particles: tuning the laser power and numerical aperture of the objective

Hossein Gorjizadeh Alinezhad and S. Nader S. Reihani

A Gaussian laser beam tightly focused through a high-numerical-aperture objective lens, so-called optical tweezers, is widely used for piconewton-range force spectroscopy. Utilizing a proper value for parameters such as bead size, numerical aperture of the objective, and power of the laser is always a challenge. Here, we show which set of values for the parameters can maximize lateral trapping efficiency. Our results show that for a high-numerical-aperture force spectroscopy, a bead with a diameter of 4–5 µm is suitable, and that for manipulation using large beads, utilizing a proper value for laser power and numerical aperture of the objective is crucial. We present a practical method for choosing the power of the laser that maximizes lateral trapping efficiency.

DOI