  Optothermal interaction of active colloidal matter can facilitate
environmental cues which can influence the dynamics of active soft matter
systems. The optically induced thermal effect can be harnessed to study
non-equilibrium thermodynamics as well as applied to self-propel colloids and
form assemblies. In this work, we employ a defocused laser trap to form
self-evolving colloidal active matter. The optothermal interaction of the
active colloids in both focused and defocused optical trap has been
investigated to ascertain their thermophoretic behavior, which shows a
long-range attraction and a short-range repulsion between the colloids. The
optical gradient field enabled attraction and the short-range repulsion between
the active colloids have been harnessed to form re-configurable dynamic
assembly. Additionally, the assembly undergoes self-evolution as a new colloid
joins the structure. Further, we show that the incident polarization state of
the optical field can be employed as a parameter to modulate the structural
orientation of the active colloids. The simple defocused optical field-enabled
assembly can serve as a model to understand the collective dynamics of active
matter systems, and can be harnessed as re-configurable microscopic engine.
