  The interplay between light and matter attracts tremendous interest for
exploring novel topological quantum states and their phase transitions. Here we
show by first-principles calculations and the Floquet theorem that a carbon
allotrope bct-C$_{16}$, a typical nodal-line semimetal, exhibits exotic
photoinduced Floquet mixed-Weyl semimetallic features. Under the irradiation of
a linearly polarized light, bct-C$_{16}$ undergos a topological phase
transition from a Driac nodal-line semimetal to a Weyl semimetal with two pairs
of tunable Weyl points. With increasing the light intensity, left-handed Weyl
points evolve from type-I into type-II while right-handed ones are always
preserved to be type-I, giving rise to photo-dressed unconventional Weyl pairs
composed of distinct types of Weyl points. Importantly, a special Weyl pair
formed by type-I and type-III Weyl points is present at the boundary between
type-I and type-II states. The Floquet Fermi arcs connecting the projections of
two different types of Weyl points are clearly visible, further revealing their
unique topological features. Our work not only realizes promising
unconventional Weyl pairs but also paves a reliable avenue for investigating
light-induced topological phase transitions.
