Third order nonlinear optical features of Bi2Fe4O9 multiferroic near antiferromagnetic phase transitions

Abstract

We have found substantial increase of the infrared third harmonic generation (THG) for the fundamental wavelength 9.4 μm of microsecond CO2 laser for Bi2Fe4O9 microcrystalline powders. Additional enhancement of the THG signal was achieved by use of Er:glass 20 ns laser generating at 1540 nm before the IR probing of the THG. At the same time the analogous effect for the photoinduced two-photon absorption (TPA) was substantially less. The observed effect is explained within a framework of phenomenological description. Principal role here is played by magneto-electric interactions due to interactions of ferroelectric polarizations and ferromagnetic states. The observed effect may be used for creation of IR laser magneto-optical materials.