Research On Color Ghost Imaging And Its Related Problems

Ghost imaging is a novel optical imaging technique which has become increasingly popular over the last decade. Difference from the classical optical imaging, in ghost imaging setup the object’s image is retrieved by using two spatially correlated light beams: the reference light beam, which never illuminates the object and is directly measured by a detector with spatial resolution(i.e., Charge-coupled Device), and the object light beam, which, after illuminating the object is measured by a bucket detector with no spatial resolution. By correlating the photocurrents from the two detectors, the “ghost” image is retrieved. It is noted that the “ghost” image is not retrieved by measuring each light beam. Previous studies of ghost imaging is based on the source with single wavelength, thus a monochromic ghost image can be obtained. However, the monochromic image is not conducive observation and its image quality is very low. Consequently, it is necessary to develop the ghost imaging technique from monochrome to color.In this paper, we developed the ghost imaging from monochrome to color, and proposed the pseudo-color ghost imaging of black-and-white object. Moreover, we analyzed several other issues about ghost imaging. The main contents are as follows:First, we investigated the color of ghost imaging with pseudo-thermal and quantum source. We found that the color of degenerate-pseudothermal and computational ghost imaging is the same as the light source or the light interacted with object. However, the color of quantum and nondegenerate-pseudothermal ghost imaging is a composite color that depends on the object and reference lights, which is different from the classical optical imaging. Furthermore, we found that the color of ghost imaging can be different from the color of the light illuminated with the object. Generally, a monochromic image can be obtained by the quantum ghost imaging, while the monochromic and colored image can be obtained by the pseudo-thermal ghost imaging. Then, we analyzed the multi-wavelength pseudo-thermal ghost imaging with rotating ground glass plate(RGGP) and spatial light modulator(SLM), respectively. Analysis shows that the N-wavelength ghost imaging with RGGP produces N ghost images incoherently added together to form one colored ghost image whose signal-to-noise ratio(SNR) is N times the one of single-wavelength ghost imaging. The N-wavelength ghost imaging with SLM produces 2N ghost images incoherently added together to form one colored ghost image whose SNR is2 N times the one of single-wavelength ghost imaging. The inhibition of noise of multi-wavelength ghost imaging with SLMS and RGGP can be explained by the extra channel theory.Second, we proposed three pseudo-color ghost imaging schemes. We obtained a colored ghost image of a black and white object with a real-time pseudocolor coding technique. We analyzed the equal spatial frequency pseudocolor coding and equal density pseudocolor coding, respectively. The results show that it is better than the ghost image obtained by a single-wavelength light source. However, limited by the spatial filtering, the SNR of the pseudo-color ghost image obtained by the real-time pseudocolor ghost imaging is low. Therefore, we proposed the phase modulation pseudocolor encoding ghost imaging that overcomes the disadvantages of other methods involved spatial filtering. Thus, the pseudocolor ghost image achieved by this imaging scheme is better than that obtained by spatial filtering in terms of brightness, color, and signal-tonoise ratio. However, phase modulation pseudocolor encoding ghost imaging is not real-time. In order to obtain a pseudo-color ghost imaging with real-time and high SNR, we propose a new pseudocolor encoding imaging technique, which we name pseudocolor ghost encoding imaging, to solve this problem effectively. The essential idea is to utilize the nondegenerate wavelength photon correlation to increase the number of channels without increasing the number of wavelengths, which masterly overcomes the limitation of spatial filtering first to our knowledge. Thus, the SNR can be dramatically improved by the effect that multichannel inhibits the noise.Third, we also studied other related issues about ghost imaging. We presented 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. Moreover, the ghost imaging with nonvisible light produces a visible and colorful ghost image. Since the ghost imaging comes from the intensity correlations, the ghost imaging effectively overcomes the effect of the interference light. We present an imaging scheme that is able to achieve the ghost imaging with broad distance. The physical nature of our scheme is that the different wavelength light beams are separated in free space by an optical media according to the slow light or dispersion principle. Meanwhile, the equality of the optical distance of the two light arms is not violated. Our work shows that a monochromic ghost image can be obtained in the case of RGGP. More important, the position(or distance) of the object can be ascertained by the color of the ghost image. Thus, the imaging and ranging processes are combined as one process. In the case of SLM, we can obtain a colored ghost image regardless of where the object is. We analyze the effects of light intensity on reflective ghost imaging with thermal source. We find that the brightness of reflective ghost image can be changed by modulating the light intensity of the source and the splitting ratio of the beam splitter. The SNR depends on the light intensity of source, and can be changed by the splitting ratio. However, the image contrast of the reflective ghost image does no affected by the light intensity.