  Increasing any degree of freedom of light beam may open a wide application
area of this special light beam. Vortex beam with a dimension of orbital
angular momentum (OAM) as a useful light source has been widely applied in many
fields. Here, unique multicolor concentric ultrafast vortex beams (MUCU-VBs),
which are also named ultrafast photonic rainbow, with controllable orbital
angular momentum are firstly generated using cascaded four-wave mixing (CFWM)
in an yttrium aluminum garnet (YAG) plate. Up to 9 multicolor concentric
annular ultrafast vortex sidebands are generated simultaneously. The
topological charges of the sidebands, which are controllable by changing the
topological charges of the two input pump beams, are measured and in according
with the theoretical analysis very well. The novel MUCU-VBs can be manipulated
simultaneously in temporal, spatial, spectral domains and OAM state, which open
more than one new degree of freedoms of vortex light beam and will be of wide
and special applications, such as multicolor pump-probe experiments,
simultaneous microparticle manipulation and exploring, and optical
communication. Moreover, the special focusing properties of the multicolor
ultrafast sidebands, such as multi-focus of different wavelengths, may further
extend their application area.
