Complex nonlinear refractive index of DNA

Femtosecond Z-scan technique was used to determine the dispersion of the complex cubic nonlinear susceptibility (related to the nonlinear refractive index n2 and the two-photon absorption coefficient β2) of deoxyribonucleic acid (DNA) in the range of wavelengths from 530–1300 nm. The nonlinear refractive index of DNA varies from ≈ 2 × 10−15 to 1 × 10−14 cm2/W at λ = 1300–530 nm, respectively. Only a weak two-photon absorption is observed below λ = 600 nm with a nonlinear absorption coefficient β2 of about 0.2 cm/GW at λ = 530 nm. The dispersion is approximated with a simple complex expression.