  Recently single-beam intracavity optical tweezers have been reported and
achieved orders-of-magnitude higher confinement than standard optical tweezers.
However, there is only one feedback loop between the trapped particle's
three-dimensional position and the scattering loss of the intracavity laser.
That leads to the coupling effect between the particle's radial and axial
motion, and aggravates the axial confinement efficiency. Here, we present and
demonstrate the dual-beam intracavity optical trap enabling independent radial
and axial self-feedback control of the trapped particle, through offsetting the
foci of the clockwise and counter-clockwise beams. We have achieved the axial
confinement efficiency of 1.6*10^(-4) mW^(-1) experimentally at very low
numerical aperture (NA=0.25), which is the highest axial confinement efficiency
of the optical trap to date, to the best of our knowledge. The dual-beam
intracavity optical trap will significantly expand the range of applications in
the further studies of biology and physics, especially for a sample that is
extremely sensitive to heat.
