The laboratory develops measurement techniques for the absolute determination of the silicon lattice parameter, as well as for implementing neutron interferometry with separated crystals. These activities require the realisation of the metre and the radian through laser interferometers with picometre-level accuracy and sub-nanoradian sensitivity.
The main activities are:
The measurement of the silicon lattice parameter requires combining optical and X-ray interferometry. The measurement is carried out by relating the displacement of a crystal, measured by an optical interferometer, to the number of lattice planes, counted by an X-ray interferometer. During the measurement, the crystal trajectory must be controlled over six degrees of freedom with atomic-scale accuracy and sensitivity: 1 pm for the longitudinal position, 1 nm for the two transverse directions, 1 nrad for the pitch and yaw rotations, 1 urad for the roll one. These performances required the development of innovative measurement and control technologies. Currently, the relative accuracy of the measurement is equal to 2 x 10-9.
Implementing neutron interferometry using separate silicon crystals placed one metre apart requires a COXI system to be combined with a neutron interferometer to create a combined optical, X-ray and neutron interferometer.