Retractable YAG BSED. Tescan introduces a new fully retractable backscattered electron detector. Utilizing an annular, ITO-coated single crystal YAG scintillator, an optimized light guide design, and a precision stainless steel bellows retractor, the new BSE detector offers an unmatched combination of performance characteristics: both compositional and topographic contrast imaging, excellent fast/TV scan rate performance, superior signal/noise, and high lateral and atomic number resolution.