Laser radiation intensity limiter based on polymethine dyes

The nonlinear optical properties of a number of polymethine dyes (PD 7005, 7006, 7031, and 7098) with a fixed polymethine chain are studied upon their excitation by the focused second-harmonic radiation from a nanosecond Nd:YAG laser. It is found that PD 7098 has the minimum linear absorption over a greater part of the visible spectrum and the strongest nonlinear reverse saturable absorption. The attenuation coefficient of the 100-MW cm^-2 laser radiation in the ethanol solution of this dye is K=14. The characteristics of a single-stage high-power-laser-radiation limiter consisting of two confocal lenses with a focal distance of 5.5 cm are optimised. The maximum values of attenuation coefficients measured in experiments are 420 (for the initial transmission T₀≈50%) and 170 (T₀≈70%). The singlet—singlet absorption cross sections of the dyes are estimated from experiments. The efficient laser radiation limiter considered in the paper features a broad spectral range in the visible region and a high service time.