Forces due to pulsed beams in optical tweezers: linear effects

Area of Science:

• Physics
• Optics
• Nanotechnology

Background:

• Precise calculation of optical forces is crucial for applications like optical trapping.
• Pulsed laser beams introduce complexities not fully captured by continuous wave (CW) models.

Purpose of the Study:

• To present a method for accurately calculating optical forces from tightly-focused pulsed laser beams.
• To compare these forces with those generated by CW beams and assess the validity of CW approximations.

Main Methods:

• Utilized generalized Lorenz-Mie theory and the T-matrix method for precise optical force calculations.
• Calculated forces for femtosecond pulses of varying widths and compared them to CW beam forces.
• Investigated the impact of pulse width and particle properties on force calculations.

Main Results:

• Optical forces from pulsed and CW beams are similar, with CW approximations generally accurate for pulses >= 100 fs (differing by <1%).
• Differences increase for shorter pulses (e.g., 8% for 25 fs) and high-index particles.
• A weighted average of CW forces across spectral components offers an improved approximation.

Conclusions:

• CW laser approximations are useful for pulsed optical force calculations, especially for longer pulses.
• Understanding spectral component contributions is key to refining pulsed beam force models.
• The developed method provides a reference for validating non-linear optical effect calculations.