Abstract: The diffraction phenomenon occurred in a high-twisted nematic liquid （HNL） crystal cell is ob- served. It is known that such kind of diffraction is due to the fomiation of so-called Williams domain. How this dif- fraction depending on the magnitude and the frequency of the electrical AC field applied on the HNL cell is also studied in detail.

Key words: high-twisted nematic liquid crystal cell, Williams domain, diffraction