Multilevel Diffractive Optical Elements for high-power laser beam shaping have been designed and produced. The originality of the proposed approach rests on the realization of four phase levels reflection elements with a single etching step. Thus, if the phase change of 270° is obtained by etching a pixel element, intermediary phase difference is obtained by etching subwavelength structures of the same height with appropriate filling factor. Sizing of the subwavelength gratings required with this theory has been carry out for TE and TM polarized radiation with a rigorous electromagnetic model, the Finite Difference Time Domain method. In a first step, a test component has been realized using photolithography to validate the sizing of the subwavelength gratings. In a second step we have adapted a specific fabrication tool based on laser ablation and direct writing for greater flexibility. Characterization has been carried out with Coherence Probe Microscopy. The technique has been applied to the fabrication of a diffractive element used with a high-power CO2 laser beam for surface marking.
Low-temperature polycrystalline silicon (poly-Si) is today a promising material allowing the production of large-area thin-film transistor (TFT’s) displays. High-performance poly-Si TFT’s are currently obtained using a pulsed excimer laser beam to crystallize the amorphous deposited silicon (a-Si) film on a glass substrate. The final quality of the poly-Si devices depends on several key parameters such as the laser energy density, the beam homogeneity and the number of laser shots. However, rapid quality control is needed to optimise and stabilize the crystallization process.
In this work, the micro structural evolution of the crystallized area with the laser annealing conditions and the formation in the Super Lateral Growth (SLG) region of large grain poly-Si have been investigated by interference microscopy. Phase Stepping Microscopy (PSM), which allows nanometric measurement of surface morphology, has been used to follow the annealing process in Si thin films on glass irradiated using a large area (~ 40 cm2) and long pulse duration (200 ns) excimer (XeCl) laser.
The results of the surface morphology obtained by interference microscopy and confirmed by Atomic Force Microscopy (AFM) attest to the PSM technique being one of the most interesting alternative ways that could be used for the calibration of the laser annealing process in an industrial environment.
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