In accordance with various embodiments of the disclosed subject matter, a method for forming polycrystalline silicon thin film, a related optical film, a related polycrystalline silicon thin film, and a related thin film transistor are provided. In some embodiments, the method comprises: providing an amorphous silicon thin film; and performing a laser annealing process to convert the amorphous silicon thin film into a polycrystalline silicon thin film through generating a laser irradiation having a spatially periodic intensity distribution to irradiate the amorphous silicon thin film; wherein the spatially periodic intensity distribution comprises: a first laser intensity to form a plurality of crystal nuclei regions arranged in an array, and a second laser intensity to form a plurality of epitaxial growth regions, the second laser intensity being greater than the first laser intensity.