Abstract

Picosecond optical limiting below 10 kW was observed in five isotropic phase-shift base liquid crystals (LCs) at 532 nm using 20-ps laser pulses. The limiting power in each was about the same as that in CS₂ (8 kW) at this wavelength. The nonlinear refractive index n₂ for the LCs was more than five times smaller than that of CS₂, and the limiting originated mainly from two-photon absorption. Two-photon absorption coefficients (β) were measured for the LC samples at 532 nm. At 1064 nm no nonlinear absorption was observed and the values of n₂ for these samples were also measured at that wavelength. The well-known theory of self-focusing was extended to include two-photon absorption. This theory was used, together with the measured β and n₂, to predict the power limiting performance of these materials. The theory also predicted a self-focusing effect arising from purely two-photon absorption which is at present under experimental investigation. The LCs used are similar in composition to the widely used MBBA (p-methoxy benzylidene p-n-butylanilene) but lack the oxygen atom and are isotropic at room temperature. These materials can be used in building fast nonlinear optical devices, in addition to the power limiter described here.

© 1985 Optical Society of America