Optical limiting performances of the methyl-red dye doped nematic liquid crystal films

The optical limiting characteristics of the methyl-red-dye doped nematic liquid crystal (NLC) (5CB and E7) films have been tested, and an interesting dark spot phenomenon and a dynamic self-action diffraction ring pattern in the far field behind the sample cell have been observed. The time sequence of the dark spot formation and the dynamic self-action diffraction ring appearance has also been investigated. We found that, with increasing the energy impringing on the sample cell, the dark spot accompanied by a single outer bright ring always appears and lasts until the multiple diffraction rings form. We also found that the dark spot with a single outer bright ring in the far field corresponds to the nonlinear section of the optical limiting characteristics curves of the doped NLC films, while the onset of the multiple diffraction rings corresponds to the input damage threshold of the doped NLC film limiters. Our experimental results show that the optical limiter based on the methyl-red dye doped NLC films has a quite low optical limiting threshold and an unusually low clamped output to eye safety. In this paper, we will present how we tested the optical limiting characteristics of the methyl-red dye doped NLC films and what kind of the typical test results we obtained in the experiments. We will theoretically analyze the optical limiting mechanisms of the methyl-red dye doped NLC films. We will also discuss the advantages and some limitations of the methyl-red-dye doped liquid crystal limiters, and propose several possible solutions to these limitations.