Deciphering single- and multi-particle trapping dynamics under femtosecond pulsed excitation with simultaneous spatial and temporal resolution

Recent theoretical and experimental studies have shed light on how optical trapping dynamics under femtosecond pulsed excitation are fine-tuned by optical and thermal nonlinearities. Here, we present experimental results of nonlinear optical trapping of single and multiple polystyrene beads (of 1 μm diameter). We show how integration and synchronization of bright-filed video microscopy with confocal detection of backscatter provide both spatial and temporal resolution required to capture intricate details of trapping dynamics. Such spatiotemporal detection is promising to have far-reaching applications in exploring controlled optical trapping and manipulations harnessed by optical and thermal nonlinearities.

Red blood cell in the field of a beam of optical tweezers

We consider the effect of a tightly focused laser beam with a wavelength of 1064 nm and a power from 10 to 160 mW on red blood cells during their optical trapping with optical tweezers. It is found that the shape of a red blood cell, which alters after optical trapping, ceases to change when the trapping duration is less than 5 min and the laser beam power is less than 60 mW. At a beam power above 80 mW, the red blood cell begins to fold at a trapping duration of about 1 min, and at powers above 100-150 mW, the red blood cell membrane ruptures in 1-3 min after optical trapping. It is also found that with repeated short-term capture of a red blood cell in an optical trap, the deformation properties of the membrane change: it becomes more rigid. The obtained results are important both for understanding the mechanisms of interaction of a laser beam with red blood cells and for optimising the technique of optical experiments, especially for measuring the deformation properties of a membrane using optical tweezers.