Passive ranging and a three-dimensional imaging system through wavefront coding

A single-image passive ranging and three-dimensional(3 D) imaging system with chiral phase encoding was proposed in 2011 [Opt. Lett. 36, 115(2011)]. A new theoretical analysis of the system in space domain is presented in this paper. We deduce the analytic relationships between the object distance and the point spread function, and between the object distance and the encoded image, respectively. Both the point spread function and the processed spectrum of the encoded image have two spots, which will rotate with the variation of the object distance. Then the depth map is extracted from the encoded image and it can be used to set up 3 D images. The theoretical analysis is verified by a wavefront coding system with a chiral phase which is generated by a phase-only liquid-crystal spatial light modulator. The phase generated by the liquid-crystal spatial light modulator is more flexible than the fixed phase mask and can be adjusted in real time. It is especially suitable for observing the object with a large depth of field.     

Passive ranging of a moving sound source using three-dimensional measured information

To solve the problem of passive ranging of a moving sound source,a method of estimating the initial distance of target is presented by using the measured inform...     

Passive three-dimensional imaging using polarimetric diversity

The results of experiments in developing a method for extracting three-dimensional information from a scene by means of a polarimetric passive imaging sensor are summarized. This sensor provides a full Stokes vector at each sensor pixel location from which degree and angle of linear polarization are computed. The angle of linear polarization provides the azimuth angle of the surface normal vector. The depression angle of this surface normal vector is obtained in terms of the emitting object's index of refraction from the solution of an equation derived from Fresnel equations, Snell's law, and percent of linear polarization. Results of the application of this approach to simulated infrared polarimetric data are provided.     

Frequency-multiplexed profilometric phase coding for three-dimensional object recognition without 2pi pi phase ambiguity

A novel phase-coding technique based on Fourier-transform profilometry (FTP) is proposed for three-dimensional object recognition. Two spatially multiplexed grating patterns of different spatial frequencies are projected simultaneously onto the objects-target, and the phase changes in the distorted patterns are detected. An algebraic addition or subtraction of these phase values is utilized to code the two-dimensional plans of the objects-target with spatial harmonic modulations. The phase-coded plans of the objects and the target are cross correlated digitally to yield a high correlation peak at the target location. The 2pi ambiguity of the phase associated with FTP has been resolved in correlation results without recourse to phase unwrapping. Experimental results show an excellent discrimination capability for target recognition.     

Frequency-multiplexed profilometric phase coding for three-dimensional object recognition without 2pi phase ambiguity: errata

In the title of our previous Letter,(1) the "pi" was incorrectly printed as "mu". The correct title should be "Frequency-multiplexed profilometric phase coding for three-dimensional object recognition without 2pi phase ambiguity" as submitted.     

Simple, flexible calibration of phase calculation-based three-dimensional imaging system

One important step of phase-based three-dimensional imaging system is calibration, which defines the relationship between phase and depth data. Existing calibration methods are complicated and hard to carry out because of using a translation stage or gauge block in a laboratory environment. This Letter introduces a new simple, flexible calibration method by using a checkerboard and a white plate having discrete markers with known separation. The checkerboard determines the internal parameters of a CCD camera. The plate gives phase and depth data of each pixel to establish their relationship. Experimental results and performance evaluation show that the proposed calibration method can reliably build up the accurate relationship between phase map and depth data in a simple, flexible way.     

Holographic real-time imaging through a phase distorted medium

In this note we report on a new experiment using Fe-doped LiNbO₃ crystal (manufactured by ourselves) as a recording medium. It can compensate in real-time for the phase distorted wavefront of an object caused by a phase distorted medium (PDM). The wavefront of the object is required to pass through the PDM once only.     

利用线谱起伏实现目标测距

常见水中目标辐射噪声的线谱会随目标运动而出现强弱起伏。不同号简正波之间的干涉是目标声强随距离起伏的主要原因,利用简正波水平波数差和波导不变量之间的关系,推导了不同线谱随距离变化起伏的理论关系式。基于此关系式,提出利用两条或多条线谱声强起伏进行声源测距的方法。针对两条线谱起伏测距方法存在的旁瓣问题,解释其形成原因,并提出用多条线谱声强起伏抑制旁瓣。数值仿真验证了方法的可行性,利用多条线谱声强起伏测距的方法可有效抑制旁瓣。海试数据分析表明,当连续谱部分非常微弱无法有效测距时,利用多条线谱声强起伏测距的方法仍能稳定的估计渔船目标距离,估计距离的平均相对误差为12%。     

Layer-by-layer three-dimensional chiral photonic crystals

We fabricate and characterize polymeric three-dimensional layer-by-layer chiral photonic crystals. The obtained circular dichroism from polarization stop bands is comparable with that of recently demonstrated circular-spiral photonic crystals. Moreover, telecommunication wavelengths are easily accessible with the layer-by-layer approach; even visible wavelengths are in reach.     

Subwavelength imaging enhancement through a three-dimensional plasmon superlens with rough surface

In this Letter we investigate the subwavelength imaging of a three-dimensional plasmon superlens based on the full vector wave simulations of optical wave propagation and transmission. The optical transfer functions are computed. Comparisons are made between the results of lenses with flat and periodic/random rough surfaces. We also study the problem of practical imaging system geometry using laser as an illumination source. Results show that the lens with periodic or random roughness can reduce the field interference effects, and provide improved focus on the transmission field and the Poynting flux. We illustrate that the subwavelength roughness in a plasmon lens can enhance the image resolution over a flat lens for both matched and unmatched permittivity conditions. The enhancement of resolution occurs because the introduced subwavelength roughness can amplify the evanescent wave components and suppress the surface plasmon resonance peaks.     

Instantons and the chiral phase transition

We examine the role of instantons in the zero-temperature chiral phase transition in an SU(N) gauge theory. For a range of N_f (the number of fermion flavors) depending on N, the theory exhibits an infrared fixed point at coupling _*. As N_f decreases, _* increases, and it eventually exceeds a critical value sufficient to trigger chiral symmetry breaking. For the case N = 2, we estimate the critical values of N_f and _* due to instantons by numerically solving a gap equation with an instanton-generated kernel. We find instanton effects of strength comparable to that of gluon exchange.     

The chiral and deconfinement phase transitions

By introducing the dressed Polayakov loop or dual chiral condensate as a candidate order parameter to describe the deconfinement phase transition for light flavors, we discuss the interplay between the chiral and deconfinement phase transitions, and propose the possible QCD phase diagram at finite temperature and density. We also introduce a dynamical gluodynamic model with dimension-2 gluon condensate, which can describe the color electric deconfinement as well as the color magnetic confinement.     

Direct-to-video holographic readout in quantum wells for three-dimensional imaging through turbid media

Customized photorefractive quantum-well devices have been developed for real-time video acquisition of coherence-gated, three-dimensional images in turbid media. Large-field-of-view holographic imaging with direct video capture is now possible. We have evaluated the role of intensity-limited device performance in Fourier-plane and image-plane holography in such devices and, using near-infrared light, have imaged through turbid phantoms of 13 mean free paths' scattering depth with 50-microm transverse and 60-microm depth resolution.     

Passive scalars,three-dimensional volume-preserving maps,and chaos

The dynamics of a medium-sized particle (passive scalar) suspended in a general time-periodic incompressible fluid flow can be described by three-dimensional volume-preserving maps. In this paper, these maps are studied in limiting cases in which some of the variables change very little in each iteration and others change quite a lot. The former are called slow variables or actions, the latter fast variables or angles. The maps are classified by their number of actions. For maps with only one action we find strong evidence for the existence of invariant surfaces that survive the nonlinear perturbation in a KAM-like way. On the other hand, for the two-action case the motion is confined to invariant lines that break for arbitrary small size of the nonlinearity. Instead, we find that adiabatic invariant surfaces emerge and typically intersect the resonance sheet of the fast motion. At these intersections surfaces are locally broken and transitions from one to another can occur. We call this process, which is analogous to Arnold diffusion, singularity-induced diffusion. It is characteristic of two-action maps. In one-action maps, this diffusion is blocked by KAM-like surfaces.On leave of absence from the Departamento de Fisica, Universidad Nacional de La Plata, (1990), La Plata, Argentina.     

Phase transition in the three-dimensional chiral field

The essentially nonlinear chiral field in three dimensional space time non-renormalizable in the usual perturbation expansion is studied. We consider systematic $\text{1}\text{N}$ expansion for this model. In the framework of the latter a phase transition takes place: above the critical point the theory is in the O(N) symmetric phase, below it the O(N) symmetry breaks. The $\text{1}\text{N}$ renormalized expansion for both phases is described and the connection between the non-renormalizability of the conventional perturbation theory and the non-analytic dependence on the coupling constant is established.     

Continuous imaging space in three-dimensional integral imaging

We report an integral imaging method with continuous imaging space. This method simultaneously reconstructs real and virtual images in the virtual mode, with a minimum gap that separates the entire imaging space into real and virtual space. Experimental results show that the gap is reduced to 45% of that in a conventional integral imaging system with the same parameters.     

Passive imaging in nondiffuse acoustic wavefields

A main property of diffuse acoustic wavefields is that, taken any two points, each of them can be seen as the source of waves and the other as the recording station. This property is shown to follow simply from array azimuthal selectivity and Huygens principle in a locally isotropic wavefield. Without time reversal, this property holds approximately also in anisotropic azimuthally uniform wavefields, implying much looser constraints for undistorted passive imaging than those required by a diffuse field. A notable example is the seismic noise field, which is generally nondiffuse, but is found to be compatible with a finite aperture anisotropic uniform wavefield. The theoretical predictions were confirmed by an experiment on seismic noise in the mainland of Venice, Italy.