AA's range of AOTF (acousto-optic tunable filters) are used extensively in confocal microscopy applications. Having pioneered the development of the AOTF in response to the needs of early developers Amos and White, AA offered the first commercially available devices for OEM applications. Photon Lines are still supplying Confocal manufacturers with such devices, and their ruggedness and reliability result in virtually zero returns due to failure in the field. An AOTF is a solid-state, electronically tunable bandpass filter which uses the acousto-optic interaction inside an anisotropic medium (the refractive index varies depending on the path taken through it), in this case the crystal TeO2.