Two-wavelength ghost imaging through atmospheric turbulence

ASF-Transformer: neutralizing the impact of atmospheric turbulence on optical imaging through alternating learning in the spatial and frequency domains

Atmospheric turbulence, a pervasive and complex physical phenomenon, challenges optical imaging across various applications. This paper presents the Alternating Spatial-Frequency (ASF)-Transformer, a learning-based method for neutralizing the impact of atmospheric turbulence on optical imaging. Drawing inspiration from split-step propagation and correlated imaging principles, we propose the Alternating Learning in Spatial and Frequency domains (LASF) mechanism. This mechanism utilizes two specially designed transformer blocks that alternate between the spatial and Fourier domains. Assisted by the proposed patch FFT loss, our model can enhance the recovery of intricate textures without the need for generative adversarial networks (GANs). Evaluated across diverse test mediums, our model demonstrated state-of-the-art performance in comparison to recent methods. The ASF-Transformer diverges from mainstream GAN-based solutions, offering a new strategy to combat image degradation introduced by atmospheric turbulence. Additionally, this work provides insights into neural network architecture by integrating principles from optical theory, paving the way for innovative neural network designs in the future.

Lossy and noisy channel simulation in computational ghost imaging by using noise-induced pattern

We provide a method to evaluate effects of a lossy and noisy optical channel in computational ghost imaging (CGI) technique. Instead of preparing an external noise source, we simulate the optical channel with a basic CGI experiment using programmatically generated noise-induced patterns. By using our method, we show that CGI can reject a noise of which intensity is similar with an imaging signal intensity at a target. The results with our method are well matched with experimental ones including external noise source. This method would provide useful knowledge to analyze environmental effects in CGI without realization of the environment.

Color night vision ghost imaging based on a wavelet transform

Night vision imaging is a technology that converts objects not visible to the human eye into visible images for night scenes and other low-light environments. However, conventional night vision imaging can directly produce only grayscale images. Here, we report a novel, to the best of our knowledge, color night vision imaging method based on a ghost imaging framework and optimized coincidence measurement based on wavelet transformation. An interesting phenomenon is that color night vision image can be directly produced by this new method. To our knowledge, this is the first direct color night vision imaging method without any conventional pseudocolor image fusion techniques. The experimental results show that this method can restore color very well for some objects. Moreover, the color of the night vision image is more natural and friendly to the human eye than that of conventional color night vision images. Due to the advantages of wavelet transforms, this method has high reconstruction ability for distorted signals.

Single-pixel imaging of high-temperature objects

For visual measurement at high temperature, one challenge is how to reduce the radiation emitted by the high-temperature components themselves and the influence of hot gas flow on the image quality, which has a significant impact in fields such as aerospace or automotive manufacturing. Owing to the complicated optical imaging environment at high temperature, a new, to the best of our knowledge, image acquisition method of high-temperature components is proposed in combination with single-pixel imaging in this paper. A series of illumination patterns is emitted to the object, and the light waves measured by the single-pixel detector are used to reconstruct the image of the object. Single-pixel imaging of high-temperature objects at different temperatures and different spectral segments has been studied in this paper. The experiment proves that the method presented in this paper can decrease the strong light interference of the high-temperature object's own radiation light and reduce the halo caused by the high temperature. This study provides a good impetus for the development of single-pixel imaging in the industrial field of high-temperature components by reducing the radiation light.

Computational Ghost Imaging Based on Light Source Formed by Coprime Array

In computational ghost imaging, a spatial light modulator (SLM) can be used to modulate the light field. The relative locations and the number of light point pixels on an SLM affect the imaging quality. Usually, SLMs are two-dimensional arrays which are drawn uniformly or are randomly sparse. However, the patterns formed by a uniform array are periodic when the number of light point pixels is small, and the images formed by a random sparse array suffer from large background noise. In this paper, we introduce a coprime array based on the Eisenstein integer to optimize the light point pixel arrangement. A coprime array is widely used as a microwave radar receiving array, but less implemented in optics. This is the first time that a coprime array based on Eisenstein integer has been introduced in computational ghost imaging. A coprime array with this structure enhances the imaging quality when limited measurements are recorded, and it reduces background noise and avoids periodicity. All results are verified by numerical simulation.

Ghost imaging utilizing experimentally acquired degree of linear polarization with no prior information

Ghost imaging is developed to obtain images of the objects based on intensity correlation of illumination patterns. However, it can be hard to distinguish between objects if the difference between their reflectivities is small. Considering the difference between degrees of polarization in the reflected light from different points, we put forward a method to retrieve distribution of the degree of linear polarization, and obtain high quality image of the objects. With the illumination source being linearly polarized, two orthogonal polarization components of the reflected intensities are measured, from which we can get the distribution of the degree of linear polarization. Furthermore, for the case that the degree of linear polarization can be approximately described with two different values within the field of view, we demonstrate retrieving of the image with high contrast. Our method can be widely applied in different situations, such as extracting the image of target hidden behind disguise or getting higher contrast in bio-imaging.

Non-degenerate wavelength computational ghost imaging with thermal light

Non-degenerate wavelength computational ghost imaging with thermal light source is studied theoretically and experimentally. The acquired computational ghost images are of high quality when the wavelength of computed light is different from the light detected by bucket detector. Compared to the necessary light of short wavelength in previous ghost imaging, the use of longer wavelength light is demonstrated to bring about ghost images with higher spatial resolution, in strong atmospheric turbulence.

Theoretical and experimental study of the color of ghost imaging

In this article, the color of ghost imaging (GI) was studied theoretically and experimentally. The theoretical analysis and experimental data show that the color of GI with rotating ground glass plate and computational GI are the same as the light source. If multiwavelength source is used in these schemes, a full color image without distortion can be obtained. In contrast, the color of GI with spatial light modulator as well as that in a quantum system is a superimposed one, depending on the idle and object light beams, and following the principle of light color superposition. Correspondingly, a full color image can also be obtained under the condition of multiwavelength source, but with color distortion existing.

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.

Point-spread function in ghost imaging system with thermal light

The point-spread function (PSF) is fundamental importance in estimating the imaging resolution in optical imaging systems. By using the Collins formula, a analytical imaging formula for ghost imaging system is obtained. The intensity fluctuation correlation function can be viewed as the convolution of the original object and a PSF. The imaging resolution is determined by the width of PSF. Based on the optical transfer matrix theory, we present the analytical formula describing the width of the PSF, by which one can estimate imaging resolution of a new-designed imaging scheme when compared with that of the existing imaging system. Several typical ghost imaging systems are chosen to verify experimentally our theoretical results.

Structured image reconstruction for three-dimensional ghost imaging lidar

A structured image reconstruction method has been proposed to obtain high quality images in three-dimensional ghost imaging lidar. By considering the spatial structure relationship between recovered images of scene slices at different longitudinal distances, orthogonality constraint has been incorporated to reconstruct the three-dimensional scenes in remote sensing. Numerical simulations have been performed to demonstrate that scene slices with various sparse ratios can be recovered more accurately by applying orthogonality constraint, and the enhancement is significant especially for ghost imaging with less measurements. A simulated three-dimensional city scene has been successfully reconstructed by using structured image reconstruction in three-dimensional ghost imaging lidar.

Polarization difference ghost imaging

We propose the polarization difference ghost imaging method and experimentally demonstrate that polarization properties can provide additional information in conventional ghost imaging for object discrimination with contrast enhancement. In our experiment, two kinds of visually similar objects with different polarization properties can be separated for imaging. Meanwhile, an improved polarization difference algorithm is presented, fully utilizing the polarization discrepancy between objects and background, to further enhance the image contrast. Our work facilitates practical applications of ghost imaging.

Standoff two-color quantum ghost imaging through turbulence

Recently, a two-color quantum ghost imaging configuration was proposed by Karmakar et al. [Phys. Rev. A81, 033845 (2010)]. By illuminating an object located far away from the source and detector, with a signal beam of long wavelength to avoid absorption of short wavelengths in the atmosphere while a reference beam of short wavelength is detected locally, this imaging configuration can be appropriate for standoff sensing. In practice, the signal beam must propagate through atmosphere in the presence of serious turbulence. We analyzed theoretically the performance of this ghost imaging configuration through turbulence. Based on the Gaussian state source model and extended Huygens-Fresnel integral, a formula is derived to depict the ghost image formed through turbulence of a standoff reflective object. Numerical calculations are also given according to the formula. The results show that the image quality will be degraded by the turbulence, but the resolution can be improved by means of optimizing the wavelengths of the reference and signal beams even when the turbulence is very serious.

Visible ghost imaging with nonvisible light

In this paper, we present a new scheme of thermal ghost imaging: visible ghost imaging with nonvisible light, which can overcome the disadvantages of conventional thermal imaging. For the two light beams of the thermal ghost imaging, we use the nonvisible light (i.e., infrared light) as the object beam and the visible light as the reference beam. The ghost image obtained by the nonvisible light can be directly observed. The ghost imaging with nonvisible light produces a visible and colorful ghost image, which is better than the thermal-imaging technique in color and image quality. Since the ghost imaging comes from the intensity correlations, the ghost imaging effectively overcomes the effect of the interference light. We believe that this new ghost imaging may be developed into a new night-vision technique.

Real-time pseudocolor coding thermal ghost imaging

In this work, a color ghost image of a black-and-white object is obtained by a real-time pseudocolor coding technique that includes equal spatial frequency pseudocolor coding and equal density pseudocolor coding. This method makes the black-and-white ghost image more conducive to observation. Furthermore, since the ghost imaging comes from the intensity cross-correlations of the two beams, ghost imaging with the real-time pseudocolor coding technique is better than classical optical imaging with the same technique in overcoming the effects of light interference.