Single-photon Imaging In High-scattering Medium

High-resolution imaging in high-scattering medium(water,fog,etc.)has important application value,but the imaging resolution of traditional sonar and millimeter-wave radar is low.Laser 3D imaging technology has the advantages of high imaging resolution,long measurement distance,high sampling rate,and abundant detection information.However,in high-scattering medium,the laser energy loss is large,and the scattering noise is serious,so the measurement distance and signal-tonoise ratio cannot be satisfied for application requirements.Single-photon detection technology has extremely high sensitivity and can realize weak light detection at the single-photon level,which solves the problem of large loss of Li DAR in high-scattering medium,but the strong backscattering noise seriously affects the single-photon detection system.Aiming at these problems,this paper studies single-photon imaging technology in high-scattering medium.By modulating the wavefront of the laser beam,the size of the laser spot irradiated on the surface of the target decreases.Combined with the synchronous beam scanning technology,the receiving field of view is greatly reduced.Therefore,the backscattered noise can be effectively suppressed and the imaging resolution and signal-to-noise ratio of the Li DAR can be improved.The main work is summarized as follows:(1)A multi-depth zoom laser imaging technology is proposed,using a liquid crystal spatial light modulator to simulate a zoom lens.By loading different Fresnel lens phase images,the focal length of the lens is changed,and the focus moves to targets with different distances to improve the three-dimensional spatial resolution and signalto-noise ratio of the image.In the dense fog with the transmittance of 0.06,three targets at 6.4 m,7.7 m and 9.4 m are scanned and imaged,achieving the transverse resolution of the order of millimeters.(2)A synchronous scanning imaging technology in fog is proposed.Using the nondiffraction characteristics of Bessel beam,it can maintain a small central spot size and a stable central spot intensity ratio during the transmission process in the fog.In the transmission range from 0 to 100 m,the divergence angle is about 31 μrad.According to the beam size,the system has a receiving field of view of 60 μrad.Compared with the traditional Gaussian beam Li DAR,the synchronous scanning imaging system has better noise suppression ability in fog,which significantly improves the imaging resolution and signal-to-noise ratio.(3)An underwater single-photon imaging technology is proposed.For the underwater "blue-green window",a 532 nm pulsed laser is used,and the Bessel beam is generated by the axicon DOE.After transmitting in water for 18 m,the spot size is enlarged from 0.53 mm to 0.73 mm@FWHM,and the divergence angle is only 11 μrad.A spatial denoising algorithm is designed to efficiently remove the backscattering noise of water bodies.In the experiment,the target at the distance of 17.5 m in the water is scanned and imaged,and the imaging resolution can reach the order of millimeters,which is much higher than that of the traditional Gaussian beam Li DAR.