Instrument for measuring magnetostrictive strain of silicon-iron single crystals

An instrument is described which can measure strains of 10¿5 within ±5% over a distance of 2mm. The method is based on optical-lever amplification of the movement due to strain. A special multiple-beam interferometer is used for absolute determination of an internal secondary calibration. The latter is used during measurements of strain to make the instrument effectively a `null¿ device.