| Summary: | We studied the structural transformations and atomic rearrangements in strontium titanate (SrTiO<sub>3</sub>) via nanosecond pulsed laser irradiation-induced melting and ultrafast quenching. Using scanning transmission electron microscopy, we determine that the laser-irradiated surface in single-crystalline SrTiO<sub>3</sub> transforms into an amorphous phase with an interposing disordered crystalline region between amorphous and ordered phases. The formation of disordered phase is attributed to the rapid recrystallization of SrTiO<sub>3</sub> from the melt phase constrained by an epitaxial relation with the pristine region, which eases up on the surface, leading to amorphous phase formation. With electron energy-loss spectroscopic analysis, we confirm the transformation of Ti<sup>+4</sup> to Ti<sup>+3</sup> due to oxygen vacancy formation as a result of laser irradiation. In the disordered region, the maximum transformation of Ti<sup>+4</sup> is observed to be 16.2 ± 0.2%, whereas it is observed to be 20.2 ± 0.2% in the amorphous region. Finally, we deduce that the degree of the disorder increases from atomically disordered to amorphous transition in SrTiO<sub>3</sub> under laser-irradiation. The signatures of short-range ordering remain similar, leading to a comparable fingerprint of electronic structure. With these results, this study addresses the gap in understanding the atomic and electronic structure modified by pulsed laser irradiation and functionalizing pristine SrTiO<sub>3</sub> for electronic, magnetic, and optical applications.
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