Optical length determinations in the diamond-anvil cell

Sample dimensions can be measured optically at high pressures to a precision of about 65 nm. Using an image-shearing device and a gasketed diamond-anvil cell, linear strains can be determined to about one part in 103 for typical sample dimensions (∼100 μm). This technique complements x-ray diffraction measurements in that optical length determinations are rapid, and can be applied to samples that are amorphous or of low atomic number. Compressibility at high temperatures and creep deformation under nonhydrostatic stresses can also be measured optically. We illustrate this method by successfully measuring the hydrostatic compression of gold to 7 GPa, using some of the smallest samples for which length changes have been determined at high pressures (∼40 μm).