Research On Distance Measurement Based On Highsensitivity Laser Interferometry

Laser interferometry technology has the highest measurement accuracy in displacement,distance and parts profile measurement,which is widely used in automobile manufacturing,parts inspection,aerospace,semiconductor manufacturing and other fields.Laser interferometer can realize high precision displacement and distance measurement of long-distance cooperative targets,or realize topography inspection of noncooperative targets in a very short range.However,laser interferometer is limited by detection sensitivity in the distance measurement of longdistance noncooperative targets or in the profile measurement of large sized noncooperative targets.In view of the above problems,the distance measurement technology based on high sensitive laser interferometry is studied.A photon-counting laser interferometer for absolute distance measurement of noncooperative targets is demonstrated by using single photon detectors,and the ranging and imaging technology based on coherent detection is developed.The details are summarized as follows:1.A new method to extend the nonambiguity range in absolute distance interferometry is proposed.A high sensitive dual-wavelength photon-counting laser interferometer for absolute distance measurement on rough surface is developed.Combined with the triangle ranging module,the nonambiguity range is extended from several hundred nanometers to 6.5 mm without wavelength calibration.A single-photon detector is designed to detect the photon level diffuse reflectance interference signal of noncooperative target,and a large range and high-precision absolute distance measurement of the noncooperative target is realized.The measurement uncertainty of the system is 18 nm.2.A high sensitive pulsed coherent lidar for noncooperative targets at the fewphoton level is proposed and experimentally demonstrated.A phase plate is used to modulate the wavefront of the laser to reduce the decoherence effect.The method of signal classification and superposition is developed to extract the echo signal submerged in noise.The system realized ranging and imaging within 100 meters.The measurement uncertainty was 1.48 cm.This system provides a new technology in automated vehicle lidar and site investigation.Furthermore,the interference fringes of noncooperative targets with different moving speeds are detected by using the characteristics of the serious difference between the two coherent beams.The echo signal of noncooperative targets is amplified to achieve high sensitive signal detection.Compared with photon-counting method,coherent detection achieves faster speed interference fringes without time accumulation,which provides a new method for relative displacement measurement of high-speed moving noncooperative objects.3.A multi-channel laser interferometer(MCLI)is invented to improve the coordinate accuracy of the measurement system.The optical interference path is simplified as two independent modules,and the laser is stabilized by polarized absorption spectra technique.The stabled light was split to the multiple interferometers through optical fiber.Multi-pixel photon couter(MPPC)is used to realize high sensitive signal detection at the multi-photon level.Combined with MCLI,the coordinate measurement uncertainty of the single axis of the coordinate measuring machine(CMM)reduced from 1.2 ?m to 197 nm in the range of 1.0 m,and achieves the Gauge block measuremnet,fine structure analysis of small hole,and contour scanning imaging of engine blade model.This technology provides an economical and robust approach to improve the coordinate measurement precision.