Distance Measurement And Control With Phase Measurement In Homodyne Interferometry

Laser interferometry can be used to measure the absolute distance or relative displacement between objects.It is one of the mainstream methods to measure distance precisely,and is widely applied in fundamental physics research.The research group,where the author is from,has recently been conducting short range test of non-Newtonian gravitational force and precision measurement of Casimir force.Both experiments require precise measurement and control of the distance between the two objects.Considering the linearity requirement between the measured signal and the distance,and the requirement to reduce the disturbance of the environment,we choose the homodyne interferometry with common optical path to measure the displacement by directly measuring the interference phase using quadrature detection.In this paper,the scheme of quadrature detection is reviewed with either position modulation or wavelength modulation.Based on available experimental apparatuses,the experiment with the position modulation is carried out.The associated Labview program was completed,which can also be used in the wavelength modulation experiment.The measurement of the displacement and the PID control of the distance with a precision less than 1 nm are achieved,and correspondingly the systematic errors are analyzed.Considering the error caused by the modulated position and the limitation of phase modulation amplitude,a scheme based on wavelength modulation is proposed.The wavelength is supposed to be modulated by the laser diode drive current,and then the laser power is needed to be stabilized by a PID feedback control.After the analysis if the laser power stability requirement and other error budgets,the feasibility of achieving a precision of 0.20 nm is verified.