A Six-Axis Heterodyne Interferometer System for the Joule Balance

The first determination of the Planck constant with the joule balance NIM-2

“…The sources of uncertainty in length measurement system are shown in table 7. The wavelength uncertainty is larger than that in paper [11], because we used other three thermal frequency stabilization laser heads instead of one frequency offset-locked laser head to achieve stronger light intensity. The relative uncertainties of the laser wavelength are not larger than 7 × 10 -9 , which is measured with help of the iodine-stabilized HeNe laser at 633 nm.…”

“…At the same time, obvious drifting of the suspended coil and the electromagnet, which is mainly from the mechanical stress relaxation and self-heating of the coils, is also observed. In order to prevent instability of the suspended coil and the electromagnet, we used a damping device to block the swing of the suspended coil [11]. The auxiliary coils and magnet of the damping device are located outside the main magnet.…”

“…The auxiliary coils and magnet of the damping device are located outside the main magnet. Potential systematic effects from the damping device, such as the leakage magnetic field and additional vertical force, were measured and analyzed in [11], and the additional uncertainty from the damping device found to be less than 3 × 10 −8 . Thus, a laser interferometer based position locking system is employed to lock the relative positions between the suspended coil and electromagnet [12].…”

“…The adjustment proceeds until the horizontal displacement and the rotation of the coil when we apply the current into the coil across the whole range of movement have been decreased to less than 10 µm and 10 µrad respectively. Reproduced with permission from [11].…”

Zoom into picometer: a picoscale equivalent phase-difference-generating method for testing heterodyne interferometers without ultraprecision stages

“…Nowadays, more and more researchers around the world are reporting progress in picoscale resolution heterodyne interferometers, including the ones utilized in gravitational wave detection 3 and Joule balance. 4 Meanwhile, as the investigation on the optical nonlinearity existing in heterodyne interferometers goes further, several explanatory theories have been advanced and errors in nanometer and picometers have been revealed. [5][6][7] However, it is difficult and expensive to implement a picoscale experiment.…”