We have successfully trapped 2.5 micron diameter microspheres between aspheric lenses! The trap is very stable and repeatable; in the video “lens trap” below we trapped for over two hours, and then removed the bead ourselves. The bead is moving under Brownian motion, and between intensity maxima, as will be described later in this post.
The alignment of the polarization between the two trapping beams is essential. If the polarizations are the same or similar then there is interference between the light, which leads to several intensity maxima in the trap. This can lead to very unstable trapping, as seen in “Lens jump” below:
By rotating the polarization of one of the trapping beams the interference is minimized, and the bead moves to a single stable trap position, as seen in “Lens stable trapping”:
Next stop: getting it in a vacuum…