A Confocal Probe based on Time Difference Measurement

A low cost confocal probe based on time difference measurement has been developed. A tuning fork is used to modulate the focal length of the probe. An auxiliary arm is introduced to the optical system. This arm can be utilized for carrying out lateral measurement or for providing a reference signal. The position of the surface is determined by measuring the time difference between two successive peak intensities of the measuring signal or that between peak intensities of measuring and reference signals. Some key problems in probe design are discussed. A correlation based technique for determining the time difference between two peak pulses is developed. Error compensation technique for nonlinearity and other errors is introduced. The excellent performance of the probe has been proven by experiments.