Nonlinear optical limiters of laser radiation on base of reverse saturable absorption and stimulated reflection

We presented wide range of laser-radiation optical limiters that are based on different physical prinsiples, operating in 400-12000 nm spectral range with rate 100-1 ns and providing wide dynamic range of limiting required for eye and sensor protection. We propose and investigate a method for reduction of the optical limiting threshold due to the Bragg reflection in a system with distributed feedback (we use the Borman cell based on hyral LC structure with C70 fullerene dope). The limiting threshold with the Borman effect, accompanying by diffractional absorption suppress and stimulated reflection from the LC Bragg grating, is about mu J/cm(2) for nano seconds pulse. We investigate nonlinear optical limiters of laser radiation (400-1000 nn, 1 ns) based on fullerene-contained materials (solutions, liquid crystals, and polymer films), operating on the basis of reverse saturable absorption (RSA) as well as stimulated nonlinear reflection of laser radiation. Fullerenes C-60, C-70 and C-84 were studied with the second harmonic of Nd:YAG laser, 532 nm, single-mode radiation pulses of 30 ns duration and maximum energy 0.35 J. Definite thresholds of RSA limiting vary from 0.05 to 0.1 J/m(2) depending on fullerene density and limiting scheme. Dynamic range of limiting sufficiently increases for multi-pass trains, the fluence decreases up to 10000 times. We elaborate 3000-12000 nm laser-radiation attenuators based on multi-layer interference structure containing vanadium-dioxide film. It is shown that these attenuators can operate due to both amplitude and diffraction effect. Attenuation is up to 1.10(3) - 1.10(5) times for 1 MW/cm(2) beams, operating time being 30-100 ns. For sensors in cooled optical systems, radiation attenuators can be used with vanadium oxides having the phase transition at cryogen temperatures.