Induced absorption characterisation of infrared sensitive photorefractive BaTiO₃

Abstract

Photorefractive materials such as BaTiO₃ have been extensively researched over the last fifteen years, and have shown themselves to be very efficient for generation of novel self-pumped and mutually pumped phase conjugate geometries. So far, most attention has been focussed on the visible spectral region, where the efficiency has tended to be highest, and the speed of response fastest. More recently however, interest has turned towards the near-infrared spectral region, due to the increasing availability and technological importance of very efficient solid-state laser diode sources operating at the ~800nm region. Such infrared active BaTiO₃ crystals have been supplied for our use by Sandoz Huningue, and we have been investigating their unique properties for self-pumping, mutual pumping and two-beam coupling. The question of why these crystals, which are deep blue in colour, behave so well at these longer wavelengths is still open for discussion, but it undoubtedly involves their multiple dopant, many level impurity states which in turn involve both deep and shallow trap. We have characterised their behaviour therefore using simultaneous excitation from two different wavelength laser sources: a He-Ne, and a tunable Ti:sapphire, operating at ~800nm to simulate typical diode laser operation. This characterisation, together with a two-level model developed at Imperial College London, has allowed us to evaluate the relevant material parameters for these blue crystals, thus generating feedback for the crystal growers who seek to improve the material response out to beyond 1µm.

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ORCID for R.W. Eason: orcid.org/0000-0001-9704-2204

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