Using spectroscopic ellipsometry, the room temperature refractive index and absorption versus wavelength of the ferroelectric antiferromagnet bismuth ferrite, BiFeO3, are reported. The material has a direct band gap at 442nm wavelength (2.81eV). Using optical second harmonic generation, the nonlinear optical coefficients were determined to be d15∕d22=0.20±0.01, d31∕d22=0.35±0.02, d33∕d22=−11.4±0.20, and ∣d22∣=298.4±6.1pm∕V at a fundamental wavelength of 800nm.

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O.; Krishnamurthi, M.; Denev, S.; et al., "Two-phonon coupling to the antiferromagnetic phase transition in multiferroic BiFeO(3)," Appl. Phys. Lett. 92, 022511 (2008); http:// dx