Self-diffraction of CO2 laser radiation in nematic liquid crystals near a nematic–isotropic liquid phase transition

Experimental and theoretical investigations were made of self-diffraction of CO₂ laser radiation in absorbing nematic crystals. A considerable increase in the signal-wave gain occurred as a result of transfer of energy from the pump radiation near a nematic–isotropic liquid phase transition (in this case the absolute gain of a weak infrared wave reached 600%). A theoretical interpretation of the effect was based on a model of a thermal nonlinearity of a nematic liquid crystal near the phase transition.