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

Abstract

We presented wide range of laser-radiation optical limiters that are based on different physical principles, 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. 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<SUP>2</SUP> for nano seconds pulse. We investigate nonlinear optical limiters of laser radiation based on fullerene-contained materials, operating on the basis of reverse saturable absorption (RSA) as well as stimulated nonlinear reflection of laser radiation. Fullerenes C<SUB>60</SUB>, C<SUB>70</SUB> and C<SUB>84</SUB> 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/M²) 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 containing vanadium-dioxide film. It is shown that these attenuators can operate due to both amplitude and diffraction effect. Attenuation is up to 1x10³- 1x10⁵ times for 1 MW/cm² 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.