Comparative study of femtosecond and conventional optical tweezers

Abstract

We present a comparative study of continuous-wave (CW) and pulsed optical tweezers for trapping polystyrene beads with radii of 250 nm, 500 nm, and 1 μm, using five different laser power settings. In this study we also emphasize the importance of using femtosecond laser, which uses intense peak power pulses to generate larger gradient forces than a CW laser at very low and same average power. We could also achieve stable trapping of 250 nm particle at very low average powers of femtosecond laser. A Ti: Sapphire (MIRA 900 F) laser, capable of seamlessly switching between CW and pulsed modes, was used to ensure identical experimental conditions for both cases. The trap strength in each mode was determined by fitting the power spectrum to a Lorentzian curve. Our results show that pulsed tweezers are more effective for smaller particles, while for larger particles, both CW and pulsed tweezers perform similarly at lower laser powers. However, as the power increases, pulsed tweezers provide more stable trapping.