Third-order Nonlinear Optical Properties Of Two New Dmit Materials

With the development of optical fiber communication and the application of dense wavelength division multiplex (DWDM) technique, all-optical network is expected to be the target for the broad-band communication in the near future. Optical switches and their arrays are among the key apparatuses in all-optical network. In addition to traditional optical switching technologies, many new ones have come forth, none of whose processing speed is high enough to satisfy the requirement of this network. All-optical switches, as a result, are in demand.According to the requirement of all-optical switches, material suitable for them should possess high third-order nonlinear refractive index, low linear absorption and nonlinear absorption. Dmit salts are an important kind of organic metal charge-transfer complex. The Ï€-electron delocalization in a conjugated systems and the d-orbit of transition metal contribute to the large third-order nonlinearity and ultrafast response capability together. Two novel dmit salts (MeCu and HtCu) were synthesized and linear absorption spectra of the sample solutions were recorded.The third-order nonlinearities were investigated by the Z-scan technique, a simple, sensitive, single-beam method to determine both the nonlinear refractive index and nonlinear absorption coefficient of a given material, at a wavelength of 1064 nm with laser duration of 30 ps. Z-scan spectra reveal their negative Kerr coefficients at 1064nm and no nonlinear absorptions were observed. The nonlinear refractive index n₂ and the second hyperpolarizability γ have been determined to be 2.15×10^-11 esu and 3.23×10^-31 esu respectively for MeCu and 6.2×10^-12 esu and 9.2×10^-32 esu respectively for HtCu.That the difference between the peak and valley transmittance ΔT_p-v is proportional to the light intensity shows that the thermal-induced nonlinearity can be neglected in our experiments. Under the same light intensity, ΔT_p-v is proportional to the concentration of the solutions, indicating that the valley and peak in the Z-scan curves originated from the material, not from the solvent or the...