ElectroHolography Laboratory

Article Summaries

Created: 24 June 2015 by Jeremy Goodsell

cw Nd:YAG laser at a 1.064-μm wavelength
particles trapped:
- gold (2 to 5 μm. in diameter), silver (2 or 3 μm), and bronze (2 to 15 μm). The gold and bronze particles were almost spherical. The silver particles were small and irregularly shaped.
- Because bronze particles tend to adhere to the surface of the sample cell, probably because of electrostatic forces, they were suspended in ethanol. Other particles were suspended in water.

532 nm Verdi Laser at 1W
60 µm beam diameter at focal plane
particles used:
- 5-20 µm silicon particles (absorptive)
found that absorbing particles such as carbon and silicon particles could be readily trapped by a focused Gaussian beam without the need of any special beam engineering. Importantly, we found that spherical particles cannot be stably trapped as compared to nonspherical particles. Once a particle is trapped, its position can be altered by changing either the laser power or the focusing condition of the beam.
A series of experiments shows that the silicon particles can be trapped easily, but the trapping is not very stable and is susceptible to ambient perturbations. It seems that the particles trapped after the focal point are more stable than those trapped before the focal point

spherical abberration trap
graphite particles: 5 microns, 25-30mW
carbon nanoparticles: 1-5mW
could easily withstand air currents estimated at 10 − 50 cm/s depending on the focusing geometry and the type and size of the particles. For a fixed trapping power, a tighter focusing provides a more stable trap because in this case the intensity minima are surrounded by regions with higher light intensity