Wenlin Gong

Ghost imaging lidar via sparsity constraints

For remote sensing, high-resolution imaging techniques are helpful to catch more characteristic information of the target. We extend pseudo-thermal light ghost imaging to the area of remote imaging and propose a ghost imaging lidar system. The experimental results demonstrate that the real-space image of a target at about 1.0 km range with 20 mm resolution is achieved by ghost imaging via sparsity constraints (GISC) technique. The characters of GISC technique compared to the existing lidar systems are also discussed.

Three-dimensional ghost imaging lidar via sparsity constraint.

Compared with two-dimensional imaging, three-dimensional imaging is much more advantageous to catch the characteristic information of the target for remote sensing. We report a range-resolving ghost imaging ladar system together with the experimental demonstration of three-dimensional remote sensing with a large field of view. The experiments show that, by measuring the correlation function of intensity fluctuations between two light fields, a three-dimensional map at about 1.0 km range with 25 cm resolution in lateral direction and 60 cm resolution in axial direction has been achieved by time-resolved measurements of the reflection signals.Three-dimensional (3D) remote imaging attracts increasing attentions in capturing a target’s characteristics. Although great progress for 3D remote imaging has been made with methods such as scanning imaging lidar and pulsed floodlight-illumination imaging lidar, either the detection range or application mode are limited by present methods. Ghost imaging via sparsity constraint (GISC), enables the reconstruction of a two-dimensional N-pixel image from much fewer than N measurements. By GISC technique and the depth information of targets captured with time-resolved measurements, we report a 3D GISC lidar system and experimentally show that a 3D scene at about 1.0 km range can be stably reconstructed with global measurements even below the Nyquist limit. Compared with existing 3D optical imaging methods, 3D GISC has the capability of both high efficiency in information extraction and high sensitivity in detection. This approach can be generalized in nonvisible wavebands and applied to other 3D imaging areas.

Correlated imaging in scattering media

Imaging with the second-order correlation of two light fields is a method to image an object by two-photon interference involving a joint detection of two photons at distant space-time points. We demonstrate for the first time that an image with high quality can still be obtained in the scattering media by applying the second-order correlation of illuminating light field. The scattering effect on the visibility of images is analyzed both theoretically and experimentally. Potential applications and the methods to further improve the visibility of the images in scattering media are also discussed.We demonstrate for the first time (to our knowledge) that an image with high quality can still be obtained in scattering media by applying the second-order correlation of illuminating light field. The effect of multiple scattering on the imaging quality is analyzed both theoretically and experimentally. Potential applications and methods to further improve the imaging quality in scattering media are also discussed.

High-resolution far-field ghost imaging via sparsity constraint

Ghost imaging (GI) is a method to nonlocally image an object with a single-pixel detector. However, the speckles transverse size at the object plane limits the systems imaging resolution for conventional GI linear reconstruction algorithm. By combining the sparsity constraint of imaging object with ghost imaging method, we demonstrate experimentally that ghost imaging via sparsity constraint (GISC) can dramatically enhance the imaging resolution even using the random measurements far below the Nyquist limit. The image reconstruction algorithm of GISC is based on compressive sensing. Factors affecting the reconstruction quality of high-resolution GISC, such as the receiving systems numerical aperture and the objects sparse representation basis, are also investigated experimentally. This high-resolution imaging technique will have great applications in the microscopy and remote-sensing areas.For ghost imaging, the speckle’s transverse size on the object plane limits the system’s imaging resolution and enhancing the resolution beyond this limit is generally called super-resolution. By combining the sparsity constraints of imaging target with ghost imaging method, we demonstrated experimentally that super-resolution imaging can be nonlocally achieved in the far field applying a new sparse reconstruction method called compressive sensing. Some factors influencing the quality of super-resolution ghost imaging via sparsity constraints are also discussed.

Ghost “pinhole” imaging in Fraunhofer region

For an aperture with transverse size D, Fraunhofer region is named when the distance between the aperture and the detector is larger than D2/λ, where λ is the wavelength of the illuminating light. For a lensless system, when both reference detector and the object are located in Fraunhofer region relative to the thermal source, we demonstrate that a ghost “pinhole” camera with magnification M=z/z1 can be obtained by the second-order correlation of two light fields even if the test detector is a single pointlike detector. Effects determining the quality of ghost pinhole imaging and its potential applications are also discussed.

The influence of sparsity property of images on ghost imaging with thermal light

The influence of sparsity property of images on ghost imaging via sparsity constraints (GISC) is investigated. We find experimentally that the reconstruction quality is in proportion to the sparse ratio of images. Employing the method of representation transform to obtain different sparsity properties for the same object, the effect of three sparse representation bases on the quality of GISC is also discussed.

Improving resolution by the second-order correlation of light fields.

As important analysis tools, microscopes with high spatial resolution are indispensable for scientific research and clinical diagnosis. We report a proof-of-principle experimental demonstration of a two-arm microscope scheme and show that, by measuring the second-order correlation of light fields, more details of an object can be obtained through recording more information about the initial illumination field. The effects arising from the transverse coherence length and the axial correlation depth of the illumination field are also discussed.

Experimental investigation of the quality of lensless super-resolution ghost imaging via sparsity constraints

Both ghost imaging (GI) and ghost imaging via compressive sampling (GICS) can nonlocally image an object. We report the influence of spatial transverse coherence property of a thermal source on GI and GICS and show that, using the same acquisition numbers, the signal-to-noise ratio (SNR) of images recovered by GI will be reduced while the quality of reconstructed images will be enhanced for GICS as the spatial transverse coherence lengths located on the object plane are decreased. Differences between GI and GICS, methods to further improve the quality and image extraction efficiency of GICS, and its potential applications are also discussed. c

Multiple-input ghost imaging via sparsity constraints

Usually the test detector of a standard ghost imaging scheme is a bucket detector; here the test detector in the scheme of multiple-input ghost imaging via sparsity constraints (MI-GISC) we proposed is characterized by some sparse-array single-pixel detectors, and the propagation process between the object plane and the test detection plane is also considered. Combining ghost imaging with the targets sparsity constraints, the theory and reconstruction of MI-GISC are investigated. The property and differences between MI-GISC and compressive ghost imaging (CGI) are studied theoretically and backed up by numerical simulations. MI-GISC can be applied in a remote imaging system with a small receiving numerical aperture, improving the reconstructions quality of the target.

The influence of axial correlation depth of light field on lensless ghost imaging

The effect of axial correlation depth of light field on lensless ghost imaging system is investigated. We demonstrate that ghost imaging in spatial domain (GI) and Fourier-transform ghost diffraction (FRT) can be transformed by only increasing the transverse size of the source. The same results can also be obtained as the distance between the object and the test detector is increased. Conditions realizing GI, FRT, and ghost “pinhole” imaging are also discussed.