| The non.contact characteristics of Laser heterodyne interference make it an important part of nondestructive testing.For some special industries,it is particularly important to be able to achieve high.precision nanometer level detection.This paper aims to design and implement nanoscale laser heterodyne interference detection system.Firstly,we elaborated the principle of laser heterodyne interference detection,optimizing the optical path structure to achieve differential double optical path.We analyzed The source of nonlinear error of optical path system and classified the error into two categories.we established the nonlinear error model and simulated it.And we performed the performance testing and analyzed the main devices of the optical path system.Secondly,this paper introduced several commonly signal processing methods of laser heterodyne interference signal,deciding use FPGA as the signal processing method of the nanometer laser heterodyne interference detection system,and designed the three modules required and simulated the function of each module.Finally,we simulated the whole system,and show the figure form simulation after processing the collected signals.Through the data analysis of the static experiments and dynamic experiments by piezoelectric ceramics,the system we designed proved had good performance in anti.noise achieve 32.1dB,the interference signal strength less than 2.6% of the main frequency signal,proving the system has a high reduction degree to vibration signal(displacement signal).In the experiments of pulse laser excitation,the sample is placed at the distance of 50 mm from the shaped pulsed light source.In broadband frequency range,we detected two major displacement:4.59 nm and 2.18 nm,the corresponding vibration frequency were 1.7MHz,7.4MHz,which showed that the sample had defects.When the samples is placed at the distance of 80 mm,60mm from the point light,the main displacement which FPGA demodulated were 104.8058 nm,18.037 nm. |
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