The recent MINERVA project set out to develop new supercontinuum sources operating from 2μm up to (and beyond) 10µm together with related enabling technologies, and deploy them in a spectral-imaging system aimed at the early detection of certain cancers. As part of the project a number of Acousto-Optic devices suitable for operation with the new generation of supercontinuum sources were developed. The design and performance characteristics of any AO device are influenced by the operational wavelength. In particular, the acoustic power and hence the RF drive power required to achieve efficient diffraction scales non-linearly with increasing wavelength. As a result, care must be exercised when designing an AO device for operation at wavelengths above about 1µm, and at wavelengths beyond about 2μm the drive power requirement and consequential management of RF/acoustic energy becomes a significant issue. The criteria for selecting the most appropriate AO interaction medium is reviewed, with an emphasis on factors affecting operation at IR wavelengths. We describe some of the devices developed for operation in the 2μm-4·5μm region. These include an AO Q-Switch for operation at 2·9μm and its deployment in a record peak-power Er:ZBLAN fibre laser. Together with a series of narrowband AO Tunable Filters specifically configured for operation with single spatial-mode white-light sources. The devices, based on the quasi-collinear AO interaction utilise the acoustic power with good efficiency, reducing the required drive power. Finally we describe a technique that is particularly suited to large-aperture AO devices such as imaging AO Tunable Filters.
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