Nonlinear Optical Responses of Spin-Coated Vanadium Oxide Films
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Nonlinear Optical Responses of Spin-Coated Vanadium Oxide Films Masanori Ando1, Kohei Kadono1, Kenji Kamada1, Koji Ohta1, Jean-François Delouis2, Keitaro Nakatani2 and Jacques Delaire2 1 Osaka National Research Institute, AIST, MITI, Ikeda, Osaka 563-8577, JAPAN 2 PPSM, Ecole Normale Supérieure de Cachan, 94235 Cachan, FRANCE
ABSTRACT We report on the third-order nonlinear optical responses of V2O5 films prepared by pyrolysis of spin-coated films of vanadium 2-ethylhexanoate. Temporal behavior of third-order optical nonlinearity of the spin-coated V2O5 films was examined at a wavelength of 532 nm by the degenerate four-wave mixing (DFWM) technique using a mode locked Nd/YAG laser (35 ps fwhm). Fast relaxation with a lifetime of 25 ps and slow relaxation with a lifetime of 150 ps were observed. The nonlinear transmission experiment on the spin-coated V2O5 films using the same laser source showed that the transmittance decreased with increasing intensity of the incident light. The intensity-dependent absorption coefficients (β) were roughly estimated to be 3.5x10-5 cm/W. Transient absorption properties of the V2O5 film were measured by use of the second and third harmonics of a Q switched Nd/YAG laser (10 ns fwhm). The results observed for the nonlinear transmission and the transient absorption suggest that induced absorption would contribute to the third-order optical nonlinearity of the V2O5 films with fast response times, and also suggest that the V2O5 films have potentiality for use as optical power limiting materials.
INTRODUCTION Over the past few decades nonlinear optical properties of materials have been a topic of large interest due to their potential applicability to photonic devices such as all-optical switching, optical phase conjugation and optical power limiting. Transition metal oxides are attracting growing interest as a new class of nonlinear optical materials for two reasons. One reason is that generally transition metal oxides have advantages from the viewpoints of thermal and chemical stability and mechanical strength. Another reason is that some transition metal oxides are theoretically predicted to show large optical nonlinearity reflecting strong correlation of electrons [1]. Concerning Fe2O3, its third-order optical nonlinearity was previously measured by the third-harmonic generation (THG) technique [2]. Recently we have shown that several transition metal oxides such as V2O5, Co3O4, Fe2O3, CuO, Mn3O4 and Cr2O3 have considerably large third-order nonlinear susceptibilities (χ(3)) in the orders of 10-9-10-7 esu by degenerate fourwave mixing (DFWM) technique using pulsed laser beams with durations of 35 ps and 7 ns [3]. However, more detailed information on the third-order nonlinear optical properties of transition metal oxides is needed for elucidating the mechanism and for exploring the possibilities of applications using nonlinear optical properties. Among six transition metal oxides listed above,
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V2O5 showed largest χ(3) values by DFWM technique, 1.2x10-8 esu and 3.1x10-7 esu us
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