Abstract
We report here the first measurement to our knowledge of degenerate four-wave mixing (FWM) phase conjugation in Cr3+:Er3+:YAlO3. The chromium ion doped in a variety of crystalline hosts gives a low intensity (~kW/cm2) nonlinear system because of the long lifetime of its 2E level and the large polarizability difference between the ground and excited 2E state.1–3 FWM measurements of the grating dynamics in Cr3+:Er3+:YAlO3 show a two time constant behaviour indicating that two different Cr3+ environments are contributing to the room temperature phase conjugate signal. Our measurements show that the Cr3+ excited state population, and not excitation among the Er3+ population, gives rise to the light induced index change and that energy transfer from Cr3+ to Er3+ provides a saturable route for deexcitation of the Cr3+ grating. The dual time constant FWM behavior in Cr3+:Er3+:YAlO3 and the large nonlinearity n2 ~ 10−7 cm2/W for the chromium ion in YAlO3 (refs. 3 and 4) make this an unusual and interesting nonlinear material. Furthermore, measurement of grating dynamics offers an indirect means to study the energy transfer process from Cr3+ to Er3+. The erbium ion in various material hosts exhibits strong upconversion5 behaviour leading to the possibility of infrared upconversion among the erbium population with energy transfer to chromium for near infra-red pumped four wave mixing in Cr3+:Er3+:YAlO3.
© 1994 Optical Society of America
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