Influence of wavelengths and beam profiles of a pulsed Nd3+:YAG laser on the formation of a polycrystalline-silicon (poly-Si) on a-Si thin film is investigated. Two sets of samples of amorphous-Silicon (a-Si) thin films deposited on glass (a-Si/glass) and crystalline Si (a-Si/c-Si) substrates were treated with different laser-fluence values. After the laser treatment, the films were analyzed by a scanning electron microscope, the Raman spectroscopy technique and the resistance-measurement technique. In the case of the third harmonics (355 nm) of the Nd3+:YAG laser, poly-Si films were obtained with laser-fluence values ranging from 260 mJ/cm2 to 560 mJ/cm2, where as in the case of the second harmonics (532 nm), the process window for the formation of poly-Si films, in terms of the laser fluence, was ranging from 300 mJ/cm2 to 480 mJ/cm2. On the other hand, in the case of samples treated with the fundamental wavelength (1064 nm), a narrow process window with higher laser-fluence values around 1100 mJ/cm2 was observed. Further, the substrate was also affected because of the higher laser-fluence value. It has also been observed that the crystallization characteristics of poly-Si films improved with the flat-top intensity distribution as compared to the Gaussian intensity distribution of the Nd3+:YAG laser beam. A theoretical simulation based on thermal modeling was performed to understand the mechanism of crystallization. © 2009 Elsevier B.V. All rights reserved.