We report on a beam shaping technique for femtosecond laser pulses based on a liquid-crystal display. The system is capable of modifying femtosecond Gaussian beams to a flattop beam. A pattern projected onto liquid-crystal display modifies the incoming Gaussian beam intensity so that flattop intensity profile is obtained. The process is monitored online using a charge-coupled device camera so that the intensity distribution of each pulse is known. An experimental example of the depth profile of a Cr layer on a Si substrate obtained using such a modified beam is presented.
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