Three-dimensional Imaging Of Photon Counting Laser Based On MCP Position-sensitive Anode Detector

Laser 3D imaging technology has the characteristics of high measurement point accuracy,high measurement point density,rich information,highly automated data processing,and highly digital products.After decades of research and development,its application field has expanded from single geodetic surveying to remote sensing and many areas of measurement,including auto-navigation of cars,remote industrial process monitoring,extraterrestrial imaging,etc.The laser 3D imaging technology combined with single photon counting has higher sensitivity,time resolution,and spectral response range,and can conduct laser detection under weak light conditions to obtain high-resolution images.In traditional single-photon counting imaging,an avalanche photodiode(APD)with a spectroscopic element and other optical elements is used to measure the light intensity in the sample space point by point by scanning the imaging surface.In the case of high-resolution requirements,not only a long scanning time is required,but also a system with a high count rate and data storage space is required.So,its real-time,dynamic,temporal and spatial resolution is relatively low.At present,most of the detectors used to realize photon counting laser 3D imaging are Geiger Mode Avalanche Photodiode(GM-APD).When GM-APD works,an external quenching circuit is required to recover to detection after avalanche occurs.Thus,the integration of the APD array is low,and its volume is huge and bulky.Moreover,the image resolution is limited by the gap between pixels.On the other hand,since the APD cannot respond to photons during the quenching process,this leads to a long dead time of the detector,which affects the imaging effect.In order to address the problem in APD-based laser 3D imaging,a photon counting laser 3D imaging system was demonstrated,in which a MCP position-sensitive anode detector was used to replace APD.As a two-dimensional planar electron multiplier,the Microchannel Plate(MCP)consists of a large number of single-channel electron multipliers arranged in parallel.The inner wall of each channel has a high multiplication.The photons are incident from the photocathode and converted into electrons.Under the action of the electric field,they continuously collide with the inner wall to achieve multiple multiplications,leading to enhanced photon imaging.The channel aperture is usually 6～12μm,and the total number of device pixels can reach millions.In addition,the sensitivity of MCP is at least 2 orders of magnitude higher than that of APD,and the dead time is smaller.Moreover,the count rate of MCP can be as high as 10~6 orders of magnitude.The MCP position-sensitive anode detector has the advantages of high signal-to-noise ratio,wide dynamic range,good drift resistance,and high spatial resolution.It has the possibility to challenge GM-APD to undertake photon counting three-dimensional imaging.The main work of this paper is to establish a photon counting 3D imaging radar system based on MCP position-sensitive anode detector.The key technologies in photon counting laser 3D imaging are studied,including time-correlated single photon counting,single photon counting detector principle,laser ranging principle,and data processing methods.The readout circuit is designed based on the crossed delay line anode.And,the laser 3D imaging experiment was conducted with the system.Two-dimensional intensity images were obtained,and the image resolution reached 100μm.The laser ranging experiment was performed by measuring the photon time of flight(TOF).The depth resolution of ranging can reach centimeter level.Moreover,the data processing method for synthesizing 3D images based on this laser 3D imaging system was explored.The 3D reconstruction of the surface of simple targets was completed,and the obtained results can restore the shape of the target surface.