Nonlinear optical activity in Bridgman growth layered compounds

Layered semiconductor compound CdI2 has been grown with the Bridgman technique and studied by nonlinear transmittance spectroscopy. The optical absorption in CdI2 shows a nonlinear transmission of the incident laser power (P0) within a lower power limit. The transmission, however, is found to saturate at high powers, giving a clamped output. The value of the incident power (P0C) at which clamping starts is also found to depend on the crystal temperature (TL). The values of POC ranges from 55 to 65 MW cm−2 for TL = 4.2-180 K. The dynamic range (DR) as a function of TL is calculated and the values are found to range from DR = 2 to 1.6. The optical limiting mechanisms are discussed. The two-photon absorption (TPA) coefficient (β) of the optical nonlinear process in CdI2 is estimated. The values are found to be within a range from β = 47 to 25 cm GW−1 and be decreasing with increasing TL. As expected for the TPA process, the experimental data within a certain range follows the linear relation: log (P0/PT) = AG + Ω(P0 − PT), where PT is the transmitted power, AG is the absorbance of the ground state and Ω is a constant depending on the absorption cross-section and the relaxation time. The values of AG and Ω estimated from the fits to the measured data vary with TL. The findings resulting from this investigation might have potential applications in optical sensors protection.