Quantum noise analysis in correlated two-photon imaging

The theoretical analysis of quantum noise is presented in a correlated two-photon imaging system with entangled photons. The noise is strongly influenced by the size and the entanglement degree of the source. An increase of the source size results in a remarkable decrease of the amplitude of the noise when the size is much smaller than the aperture of the lens, whereas the change will not be obvious if the size is close to the aperture. The difference of the effects from the source between correlated imaging formed with entangled photons and with partially coherent light is also discussed.     

Visibility of ghost imaging in a two-arm microscope imaging system

Ghost imaging with a classical thermal source is investigated in a two-arm microscope imaging system. The dependence of the imaging visibility on the aperture of the reference lens is discussed. It is shown that by using large apertures, good visibility as well as enhancing resolution can be obtained. The effects from the distance the object is moved away from the original plane are also studied, and one can obtain good visibility with a well-resolved image by changing the distance.     

Width dependence of two-dimensional photonic quasicrystal flat lens imaging characteristics

Imaging characteristics of germanium cylinder-based decagonal photonic quasicrystal flat lens have been analyzed with respect to width. The results show that the complex near-field scattering effects and the short-range interactions do not determine the occurrence of the imaging phenomenon but affect imaging characteristics. Changing the width will affect the imaging characteristics of the flat lens. As the width increases, the image power, the image quality, and the summed object–image distance change non-monotonically but stabilize gradually.     

Partially coherent light-emitting diode illumination for video-rate in-line holographic microscopy

The light of a light-emitting diode or a common thermal source, such as a tungsten filament lamp, is known to be quasi-incoherent. We generated partially coherent light of these sources with a volume of coherence in the micrometer range of 5-100 μm3 by spatial and spectral filtering. The corresponding degree of partial coherence was adapted for microscopic interference setups, such as a digital in-line holographic microscope. The practicability of the sources was determined by the spectral emittance and the resulting signal-to-noise ratio (SNR) of the detector. The microscale coherence in correlation with the SNR and its resolution for microscopy were analyzed. We demonstrate how low-light-level, non-laser sources enable holographic imaging with a video frame rate (25 frames/s), an intermediate SNR of 8 dB, and a volume of coherence of 3.4×10(4) μm3. Holograms of objects with a lateral resolution of 1 μm were achieved using a microscope lens (50×/NA=0.7) and a CCD camera featuring a 4-12 bit dynamic range.     

Generation of adjustable partially coherent bottle beams by use of an axicon-lens system

We report, what is to our knowledge, the first experimental realization of partially coherent bottle beams. It is shown that partially coherent bottle beams can be achieved by the focusing of partially coherent light with an axicon-lens system. The influence of the spatial coherence of the incident partially coherent light and other parameters, such as the radius of the limiting aperture of the axicon and the distance between the axicon and the lens, on the size of the bottle beams is investigated. We find that the longer the spatial coherence length, the larger the size of the resultant bottle beams. This dependence of the size of the bottle beams on the spatial coherence of the incident light provides a facile approach for generating adjustable partially coherent bottle beams. This kind of partially coherent bottle beam may have applications in atom optics, such as in atom trapping and atom guiding, etc.     

Doppler encoded excitation pattern tomographic optical microscopy

Most far-field optical imaging systems rely on lenses and spatially resolved detection to probe distinct locations on the object. We describe and demonstrate a high-speed wide-field approach to imaging that instead measures the complex spatial Fourier transform of the object by detecting its spatially integrated response to dynamic acousto-optically synthesized structured illumination. Tomographic filtered backprojection is applied to reconstruct the object in two or three dimensions. This technique decouples depth of field and working distance from resolution, in contrast to conventional imaging, and can be used to image biological and synthetic structures in fluoresced or scattered light employing coherent or broadband illumination. We discuss the electronically programmable transfer function of the optical system and its implications for imaging dynamic processes. We also explore wide-field fluorescence imaging in scattering media by coherence gating. Finally, we present two-dimensional high-resolution tomographic image reconstructions in both scattered and fluoresced light demonstrating a thousandfold improvement in the depth of field compared to conventional lens-based microscopy.     

Imaging Properties of the Schwarzschild Soft-X-ray Microscopes

Abstract

The imaging properties of the soft-X-ray microscopes composed of a Schwarzschild objective and a grazing incidence mirror condenser are discussed. Fundamental formulae on the partially coherent transfer function, the resolution of a two-point object and the edge response have been derived by consideration of the optical properties of an object in soft-X-ray regions. Then these imaging properties for the microscopes are investigated with the formulae and compared with those for a normal circular pupil system.     

Coincidence fractional Fourier transform implemented with partially coherent light radiation

We introduce the coincidence fractional Fourier transform (FRT) implemented with incoherent and partially coherent light radiation. Optical systems for implementing the coincidence FRT are designed. The results show that the visibility and quality of the coincidence FRT of an object are closely related to the light source's transverse size, coherence, and spectral width. As an example, we numerically study the coincidence FRT of a single slit.     

Spectral switches of partially coherent light focused by a filter-lens system with chromatic aberration

It is shown that when partially coherent polychromatic light is focused by a filter-lens system with chromatic aberration, a spectral shift exists in the focused field, and a spectral switch that is defined as a sharp transition of the spectral shift also takes place at some positions of the focused field. The influence of the chromatic aberration of the lens, the coherence of the partially coherent light in the filter (a circular aperture), the radius of the aperture, and the spectral width of the partially coherent light in the aperture on the spectral shift and the spectral switch are investigated in detail. The numerical results show that these parameters affect the spectral shift and the spectral switch significantly. Potential applications of the spectral shift and the spectral switch of the partially coherent light are discussed.     

Numerical experiment of the Shannon entropy in partially coherent imaging by Koehler illumination to show the relationship to degree of coherence

This paper describes the Shannon entropy in a partially coherent imaging system with Koehler illumination. Numerical simulation shows that the entropy has a one-to-one relationship with the normalized mutual intensity given by the van Cittert-Zernike theorem. Analytical evaluation shows that the entropy is consistent with the definition of coherence and incoherence, which is also verified by numerical simulations. Additional numerical experiments confirm that the entropy depends on the source intensity distribution, polarization state of the source, object, and pupil. Therefore, the entropy quantitatively measures the degree of coherence of the partially coherent imaging system.     

Imaging of trace species distributions by degenerate four-wave mixing: diffraction effects, spatial resolution, and image referencing

We describe the theory of imaging by degenerate four-wave mixing (DFWM) using a standard diffraction theory of imaging by coherent light. We demonstrate that, even with the phase-conjugating geometry, no aberration correction can be achieved by DFWM imaging. We demonstrate the coherent nature of DFWM image formation using spatially modulated signals generated in flame OH in the phase-conjugating geometry. The intensity distribution in the Fourier plane of a telecentric lens system is shown to be the spatial Fourier transform of the object distribution characteristic of coherent imaging. The brightness of the DFWM signals exceeds that of similar laser-induced fluorescence signals that can be discriminated by restricting the aperture of the imaging system while still allowing a spatial resolution of approximately 70 ?m. DFWM imaging with the forward-folded boxcars geometry is demonstrated and used in a simple referencing scheme to compensate for structure on the images imposed by nonuniformity of the laser beams employed. Images formed in NO are used to illustrate that structure on a scale of less than 100 ?m arising from beam inhomogeneity can be removed by this referencing technique.     

Optical imaging with a directional detector

We demonstrate a new optical imaging technique based on a directional detector that measures the intensity of light waves that propagate only in a narrow angular window around a specific direction. Light waves that propagate in other directions do not significantly affect the detector output. The directional detector is obtained by illuminating the interrogated object with a high-coherence light source and measuring the interference between the light wave reflected from the object and a reference wave. By measuring the intensity of the interference pattern with an optical detector that has a finite width and moving the object by use of a rotation stage, one can obtain the angular directionality of the filter. The use of coherent detection in the directional detector makes it possible to increase the sensitivity of the system. The directional detector was analyzed theoretically and demonstrated experimentally for a Gaussian beam scattered from a conducting cylinder. The interference enabled us to theoretically increase the angular resolution by a factor of approximately 10 and experimentally by a factor of 8.5. A configuration for using a directional detector array to reconstruct a two-dimensional object is suggested. Since the directional detector makes it possible to reduce the effect of diffraction and scattering, reconstruction techniques based on nondiffracting sources, as implemented in x-ray tomography, may be used.     

激光相干阵列成象雷达系统光束整形的研究

激光相干阵列成象雷达系统中本振光波前与信号光波前匹配与否直接影响系统的灵敏度和分辨力。采用共轭光栅合成技术对相干成象本振光束作整形处理，以适应探测器件列及合成输出满足最佳信噪比条件。     

Rainbow holography of a diffuse three-dimensional object with a synthetic slit

Abstract

A study of rainbow holography with a movable synthetic slit in three-dimensional (3D) space is presented. A diffuse 3D object and an imaging lens are translated uniformly along the same direction with different (or identical) speeds in the X-Y plane. The spatial frequencies of the coherent wave illuminating the object are α, 0 and γ. As a result, the synthetic slit in rainbow holography is presented at a position which depends on the translational direction of the object and the imaging lens, their relative speeds, the spatial frequency of the illuminating wave in the X ₀ direction, and the relative distance of the reference source and the reconstruction source from the holographic plate. Theoretical analysis and some experimental results are presented.     

Geometrically superresolved lensless imaging using a spatial light modulator

In this paper we introduce an imaging system based on a reflective phase-only spatial light modulator (SLM) in order to perform imaging with improved geometric resolution. By using the SLM, we combine the realization of two main abilities: a lens with a tunable focus and a phase function that, after proper free-space propagation, is projected as an amplitude distribution on top of the inspected object. The first ability is related to the realization of a lens function combined with a tunable prism that yields a microscanning of the inspected object. This by itself improves the spatial sampling density. The second ability is related to a projection of a phase function that is computed using an iterative beam-shaping Gerchberg-Saxton algorithm. After the free-space propagation from the SLM toward the inspected object, an amplitude pattern is generated on top of the object. This projected pattern and a set of low-resolution images with relative shift are interlaced and, after applying the proper regularization method, a geometrically superresolved image is reconstructed.     

Evaluation of the spatial coherence of a light beam through transverse intensity measurements

The problem of recovering the coherence features of a partially coherent quasi-monochromatic scalar optical source, starting solely from intensity measurements on the emitted beam, is addressed in the most general way, under the paraxial approximation. In particular, it is shown that on expanding the beam emitted by the source as a bundle of partially correlated Hermite-Gaussian beams, the correlation coefficients can be recovered, in principle, simply by performing scalar products between transverse intensity distributions and suitably defined functions.     

On the Study of Partial Coherence via Diffraction Experiments

The radiation pattern of a circular aperture illuminated both uniformly and non-uniformly by partially coherent light is calculated in the diffraction limit. Furthermore, the angular resolution of a circular lens is examined for four reasonable correlation functions. Also the effects of the parameters—partial coherence, misalignment, and non-uniform illumination—on the diffraction pattern of a double slit are considered for a particular mathematical model of the radiation field. The results of this analysis are used to discuss the the use of diffraction experiments in the study of the coherence properties of light.     

Detection of the Object Velocity Using Doubly-scattered Dynamic Speckles Under Gaussian Beam Illumination

Abstract

The dynamic properties of doubly-scattered speckles produced at the image plane have been investigated using a scattering model that consists of a coherent Gaussian beam, a cascade of two moving diffusers and a single imaging lens. Dependence of the fluctuation speed of time-varying image speckles on the velocities of the diffusers is found to change with the size of illuminating speckles and the width of the point-spread function of the imaging lens. When the point-spread function and the focal position satisfy certain conditions, three kinds of velocity information—the velocity of each diffuser, the average velocity of the diffusers and the velocity difference between the diffusers—can be obtained by measuring a temporal correlation length of the time-varying speckle intensity. Experimental results confirm the theoretical predictions.     

Coherent-mode decomposition of partially polarized,partially coherent sources

It is shown that any partially polarized, partially coherent source can be expressed in terms of a suitable superposition of transverse coherent modes with orthogonal polarization states. Such modes are determined through the solution of a system of two coupled integral equations. An example, for which the modal decomposition is obtained in closed form in terms of fully linearly polarized Hermite Gaussian modes, is given.     

Spatial partially coherent imaging

We introduce the partial coherence response function for describing the behaviour of imaging systems under spatial partially coherent illumination in the centre and the diierence coordinates notation. It involves the impulse response of the system and the spatial coherence properties of the illumination. It is shown that this function is the image cross-spectral density for a Young's pair of pinholes attached at the object plane. Furthermore, the partial coherence response function and the partial coherence transfer function constitute a Fourier pair on which the Fourier representation of partially coherent imaging can be based.