Characteristics of a low f-number broadband visible thermal optical limiter

The operation of a wide field-of-view optical limiter is described for self-defocusing type nonlinear refractive materials, and design strategies were developed with the aid of numerical modeling. Experiments with a cell thickness on the order of the Rayleigh length (25–100 µm) were conducted with 6 and 30 nsec pulse lengths (single shot) at a wavelength of 532 nm. Broadband optical limiting with the transmitted fluence below the eye MPE (maximum permissible exposure) level was achieved using nigrosin dye dissolved in CS 2, owing to the large thermal nonlinearity of the solvent, and the large changes in the refractive index allowed by a liquid. The device performance was accurately predicted by the numerical model up to the point of dielectric breakdown. Using 6 nsec pulses, we measured a limiting threshold energy of 40 nJ, which corresponds to a fluence of only 100 mJ/cm 2 in the solution, in an f/5 optical system with neutral gray transmission of ~ 50%.