  Needle-like electromagnetic fields has various advantages for the
applications in high-resolution imaging, Raman Spectroscopy, as well as
long-distance optical transportation. The realization of such field often
requires high numerical aperture (NA) objective lens and the transmission
masks. We demonstrate an ultralong needle-like focus in the optical range
produced with an ordinary lens. This is achieved by focusing a symmetric Airy
beam (SAB) generated via binary spectral modulation with a digital micromirror
device(DMD). Such amplitude modulation technique is able to shape traditional
Airy beams, SABs, as well as the dynamic transition modes between the
one-dimensional(1D) and two-dimensional (2D) symmetric Airy modes. The created
2D SAB was characterized through measurement of the propagating fields with one
of the four main lobes blocked by an opaque mask. The 2D SAB was verified to
exhibit self-healing property against propagation with the obstructed major
lobe reconstructed after a certain distance. We further produced an elongated
focal line by concentrating the SAB via lenses with different NA's, and
achieved an ultralong longitudinal needle focus. The produced long needle focus
will be applied in optical, chemical, and biological sciences.
