  A light beam propagating with an infinite anti-diffracting distance requires
infinite power to preserve its shape. However, the fundamental barrier of
finite power in free space has made the problem of diffraction insurmountable
over the past few decades. Here, to overcome this limitation, we report an
approach that employs the multiple energy oscillation mechanism, thereby
permitting the creation of a light beam with an ultralong anti-diffracting
distance in free space. The anti-diffracting distance is no longer restricted
by finite power in free space but instead depends on the number of energy
oscillations. This unprecedented propagation behavior is attributed to a new
understanding of non-diffractive light beam: when an anti-diffracting light
beam completely discharges its energy, it cannot recharge again. A versatile
optical pen is therefore developed to manipulate the number, amplitude,
position and phase of energy oscillations for an arbitrary numerical aperture
of a focusing lens so that energy recharge can occur in free space and multiple
energy oscillations can be realized. A light beam with a tunable number of
energy oscillations is eventually generated in free space and propagates along
a wavy trajectory. This work will enable extending non-diffractive light beams
to an expanded realm and facilitate extensive developments in optics and other
research fields, such as electronics and acoustics.
