  Photonic nanojets have been brought into attention ten years ago for
potential application in ultramicroscopy, because of its sub-wavelength
resolution that can enhance detection and interaction with matter. For these
novel applications under development, the optical trapping of a sphere acts as
an ideal framework to employ photonic nanojets. In the present study, we
generated nanojets by using a highly focused incident beam, in contrast to
traditional plane waves. The method inherits the advantage of optical trapping,
especially for intracellular applications, with the microsphere in equilibrium
on the beam propagation axis and positioned arbitrarily in space. Moreover,
owing to optical scattering forces, when the sphere is in equilibrium, its
center shifts with respect to the focal point of the incident beam. However,
when the system is in stable equilibrium with a configuration involving optical
tweezers, photonic nanojets cannot be formed. To overcome this issue, we
employed double optical tweezers in an unorthodox configuration involving two
collinear and co-propagating beams, the precise positioning of which would turn
on/off the photonic nanojets, thereby improving the applicability of photonic
nanojets.
