Self-focus medium-liquid crystal was placed between two BK7 glass plates

and the grating with the triangle groove was caved on the internal surface of one of glass plates for making nonlinear modulation grating.An Ar ion laser beam with 5145nm wavelength was irradiated perpendicularly to the grating surface and was focused on the liquid crystal.The diffractive angle of the laser beam was depended on the grating period.The intensity of 0-order beam was depended on the depth of the grating groove.Because the liquid crystal is self focus medium

the increasing of laser power density focused on the liquid crystal can change the refractive index difference between the liquid crystal and BK7 glass plate.Under a specified value of the laser power

it was obtained by experiment that the laser power density focused on the liquid crystal was 0.5kW/cm

2

the refractive index difference between the liquid crystal and BK7 glass plate was nearly equal to 0.As a result

the grating in this structure was covered

the various diffracted orders of the transmitting sample almost disappeared

only 0-order beam was left;deviating from this value

the grating reappeared

the various diffracted orders appeared immediately

0-roder beam was weakened.This modulation effect is on physical basis for adaptive optical limiting of the nonlinear grating.The effect of the adaptive optical limiting has the features of large bandwidth and high speed optical limiting.So it has important application prospects in tunable protection of lasers.