Keshu Zhang

Common characteristics shared by different differential phase contrast imaging methods

There are many variations of differential phase contrast imaging methods. Although these imaging methods are different in configuration, they are alike in imaging by extracting differential phase information through the evaluation of the refraction angles. In this paper, we investigate common characteristics shared by various different differential phase contrast imaging methods.

Linear frequency-modulated continuous-wave ladar system for synthetic aperture imaging

A novel and high-efficiency linear frequency-modulated continuous-wave (FMCW) ladar system for synthetic aperture imaging is proposed and experimentally demonstrated. This novel system generates wide-bandwidth linear FMCW ladar signals by employing an electro-optic LiNbO3- in-phase and quadrature modulator with an effective bias controller. The effectiveness of the proposed system is experimentally validated. Optical synthetic aperture images are obtained by using two 0.41 cm aperture diameter telescopes at the distance of 1 km. The resolution of these images can reach to 4 cm. A resolution improvement by about 10 times is achieved when compared with the conventional real aperture imaging system.

Generalization of DEI Methods in Grating‐Based Phase‐Contrast Imaging

It has been shown that grating based x‐ray phase contrast imaging (GPI) can be performed on x‐ray tubes and therefore has a great potential for a wide application in many fields. So far to extract and to separate the phase information from other contributions, a phase‐stepping approach is normally adopted. One of the gratings is scanned transversely to the incident beam while acquiring multiple projections of the sample. However, during the grating scanning, the sample is supposed to be static, and the resulting poor time resolution is one of the major drawbacks of this method. It is clear that a method that would extract the phase information without the need of multiple stepping would be a breakthrough enabling fast, highly sensitive (phase‐contrast) x‐ray imaging. According to the similar physics and mathematics between diffraction enhanced imaging (DEI) and GPI, here we report how the DEI methods can be generalized for GPI and how GPI can use the same acquisition procedure as the conventional absorpti...

Experiment of inverse synthetic aperture ladar at 1.1km

This manuscript describes an airborne SAL system for remote targets imaging. We have recently completed an experiment of ISAL at 1.1 km outdoor using the system. Relative motion was provided by a rotating platform with three cubes on while the SAL system kept stationary. System, signal collection, processing and the results are described in the paper. The result showed that the system had the ability to image for moving targets. Accurate rotating platform and complex target will be used to achieve further ISAL experiments on the next stage.

Focusing of the FMCW synthetic aperture ladar data

Synthetic aperture ladar (SAL) is a new remote sensing sensor and has the potential for much finer resolution than synthetic aperture radar (SAR) for its much shorter wavelength. For SAL system, frequency modulated continuous wave (FMCW) is usually used to achieve large time-bandwidth product (TBP). In this paper, we proposed the method for focusing the FMCW-SAL data. Firstly, we derived the signal model for FMCW-SAL without the start/stop approximation. And based on the signal model, imaging method is proposed. Then, the motion compensation for SAL is discussed. At last, we showed the imaging results for both the ground-based SAL and the airborne SAL. The imaging results verified the effectiveness of the proposed focusing method.

Experiment of inverse synthetic aperture LADAR on real target

In this manuscript, an Inverse Synthetic Aperture LADAR (ISAL) system at 1.55 μm wavelength is introduced. We have recently completed an imaging experiment on real target 1.1 km away from laser radar by using the system and obtained a series of images of the target, an aircraft model, with cm-level range resolution and mm-level cross-range resolution, which is due to the large bandwidth transmitting signal and the μm-level wavelength of laser. The results of experiment prove that the inverse synthetic aperture LADAR system has the ability to imaging a real target with high-resolution from a long distance, which transcends the diffraction limit for the effective aperture size of the receive telescope.

Synthetic aperture LADAR at 1550 nm: system demonstration, imaging processing and experimental result

In this manuscript, we propose and experimentally demonstrate our synthetic aperture LADAR (SAL) system. The system could obtain imageries in a few milliseconds with resolution of 5 cm from a long distance. Fine resolution in the range dimension was obtained by transmitting LADAR signal with large bandwidth. While in the cross-range dimension, the large synthetic aperture diameter provided fine resolution. By employing continuous translational motion of SAL system, a large aperture diameter was obtained through synthetic aperture processing. So the diffraction limit of real aperture diameter was overcome and finer resolution was achieved. Indoor and outdoor experiments were both performed and the corresponding results were showed. Results validated the feasibility of our system and processing algorithm.