Ghost imaging lidar system for remote imaging.

Research towards practical applications of ghost imaging lidar system especially in longer sensing distance has been urgent in recent years. In this paper we develop a ghost imaging lidar system to boost an extension of remote imaging, where the transmission distance of the collimated pseudo-thermal beam can be improved hugely over long range and just shifting the adjustable lens assembly generates wide field of view suiting for short-range imaging. Based on the proposed lidar system, the changing tendency of illuminating field of view, energy density, and reconstructed images is analyzed and verified experimentally. Some considerations on the improvement of this lidar system are also discussed.

Propagation dynamics and crosstalk of orbital angular momentum beams influenced by a supersonic wind-induced environmental disturbance.

Near field airflow induced by wind is an important factor influencing vortex beams propagation under airborne optical communication, and the cross-talk among different orbital angular momentum (OAM) modes occurs in OAM-based optical communication. In this paper, the propagation of vortex beams through a supersonic wind-induced random environment is investigated. The wind-induced phase model is firstly validated by wind tunnel experiment, with the phase model, vortex beams propagation under supersonic wind condition is analyzed, and the spiral spectrum distortion is discussed in detail. It is demonstrated that the larger wind velocity and boundary-layer thickness leads to the enhanced distortion and spiral spectrum expansion of OAM beams. The behavior of multiplexed vortex beams influenced by supersonic wind is also studied, and the effect of the topological charge interval is given. Our results may provide a powerful tool to estimate the effect of a random airflow environment on OAM-based communication performance under airborne condition.

Enhancing critical resolution of a ghost imaging system by using a vortex beam.

In an imaging system, resolution and signal-to-noise ratio (SNR) are two important indexes to characterize imaging quality. Ghost imaging is a novel imaging method whose imaging resolution and SNR are affected by the speckle size. In this paper, the relation between speckle size and resolution as well as that between speckle size and SNR in the GI system is analyzed in detail. It is shown that the critical resolution, resolvable minimum-separation between two adjacent objects, is approximately equal to the speckle size (speckle diameter). There exists an optimum SNR when the speckle size is larger than the object size. Based on our conclusion, we propose a scheme to enhance the critical resolution of the GI system by using a vortex beam, and the enhancement ability under different topological charges is clearly presented, which can be quantized by a simple formula.

Improving the signal-to-noise ratio of computational ghost imaging of a reflective object with a rough surface by Hadamard modulated light field.

We propose an optimization scheme to improve the reconstruction quality of computational ghost imaging (GI) of a reflective target with a rough surface by using the Hadamard modulation light field (HCGI). By comparison with computational GI with a traditional Gaussian light field (GCGI), the signal-to-noise ratio of GCGI is quite bad, and it is difficult to distinguish the imaging signal from the background when the surface roughness of the object is higher, while a ghost image with better quality can be obtained by HCGI. The difference is explained by comparing the distribution of the correlation coefficient. Additionally, it is found that HCGI has better noise robustness in comparison with GI with other random coded patterns.

Ghost imaging influenced by a supersonic wind-induced random environment.

Near field airflow induced by wind is an important factor influencing imaging quality when the imaging system is placed on a moving platform with high speed, such as airborne imaging. In this Letter, ghost imaging through an airflow environment is experimentally and numerically investigated. The experiment is performed with a wind tunnel, and imaging quality decreases with wind velocity. The simulation model of ghost imaging through this kind of environment is proposed, and simulation results match well with experiments. With the model, imaging results are extended into the supersonic wind region with the effects of airflow factors discussed in detail, and a comparison between airflow and atmosphere turbulence is presented. The results can find potential applications in optical imaging and may be a powerful tool to estimate the effect of airflow on performance of the imaging system.

Ghost imaging for detecting trembling with random temporal changing.

The imaging environment can be destabilized for moving objects and imaging platforms, thus leading the detection to be random trembling, which is detrimental to object reconstruction. In this Letter, we experimentally investigate ghost imaging for detecting trembling with random temporal changing, and an improvement method based on the temporal property of the imaging process is proposed. It is demonstrated that this method is effective in addressing image degradation due to the trembling disturbance and obtaining a higher-quality image of the object. The results provide a promising approach to deal with image degradation caused by an unstable environment and can find potential applications for ghost imaging in remote sensing.

Investigation on the behavior of a laser propagating through a random environment induced by wind.

Wind is an important factor in environment disturbance, and the inhomogeneous distribution of wind velocity leads to random airflow, which severely affects beam propagation. In this paper, numerical and experimental studies have been performed to investigate the behavior of a laser propagating through a random environment induced by wind, and the main focus is the beam deflection evolution under the effect of the wind velocity. The experiment is performed with the wind tunnel, and the beam deviates from the center during propagation, a process in which the average beam deflection presents an increasing trend for the larger wind velocity and the airflow interval. The simulation model of beam propagation through this kind of environment is proposed, and the numerical simulation agrees with the experimental results. With the model, the average beam deflection results are extended into the high-speed region, and the comparison between the airflow and turbulence environment is also presented. The results can find potential applications in optical propagation and communication between two moving platforms with high speed.

Effect of the collection range of a bucket detector on ghost imaging through turbulent atmosphere.

A model of the collection range of a bucket detector is proposed to investigate ghost imaging through turbulent atmosphere. The influence of the collection range of a bucket detector on the quality of ghost imaging is discussed under different turbulence intensities. The numerical results show that the quality of ghost imaging increases with increment in the collection range of the bucket detector and with a decrease in turbulence intensity. Specifically, we give a critical collection range of a bucket detector, which is the minimum collection range for ghost imaging at different turbulence intensities. Additionally, a comparison of ghost imaging through turbulent atmosphere with ghost imaging through vacuum atmosphere is provided to show the effect of turbulent atmosphere on ghost imaging.

Influence of transversely inhomogeneous pseudo-thermal light source on lensless ghost imaging.

The influence of a transversely inhomogeneous pseudo-thermal light source on lensless ghost imaging is investigated theoretically and experimentally. Based on classical optical theory, a model of lensless ghost imaging with an inside inclined light source is analyzed. We use the optical path difference between different transverse positions of the light beam to estimate the degree of inhomogeneity. The results indicate that the transversely inhomogeneous light source decreases the visibility and signal-to-noise ratio of the reconstructed image. Finally, we implement experiments to verify our results using inclined ground glass.

Reduction of the defocusing effect in lensless ghost imaging and ghost diffraction with cosh-Gaussian modulated incoherent sources.

The inhibition effect from the cosh-Gaussian modulated incoherent source on the defocusing effect is investigated theoretically in lensless ghost imaging (LGI) and ghost diffraction (LGD) systems. The corresponding numerical simulations are presented to show the influence of the cosh-Gaussian incoherent source on the defocusing effect in LGI and LGD. Compared with the widely used Gaussian incoherent source, it is shown that the defocusing effect in LGI and LGD can be greatly weakened by properly adjusting the modulation parameter ω of the cosh-Gaussian source. To explain this phenomenon, the analytical expression for point spread function of the LGI system with the cosh-Gaussian source is derived.