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Illuminated by ultrashort optical pulses, large area multiplex terahertz semiconductor emitters that work on photo-Dember currents and Schottky potentials radiate a directional electromagnetic terahertz pulse which is controlled by the angular spectrum of the incident optical beam. Using the lens that focuses the incident near infra-red pulse, we have demonstrated THz emission focusing in free space and characterized a Gouy phase shift.

Based on the modal analysis method, a model describing the output beam of a diode pumped solid state (DPSS) laser emitting a multimode beam is presented. Measuring the output beam profiles in near-field, the individual modes as well as their contributions are determined. To this purpose, the superposition principle and the angular spectrum method are employed to predict the beam profile along the propagation axis and at far-field.

Off-axis digital holography (DH) has great potential in histopathology for its high efficiency and precision. Phase distribution, usually extracted by the angular spectrum (AS) algorithm from a digital hologram, reflects important structural information of biological tissues. However, the complex structure of tissues introduces spectrum aliasing of the hologram, making the AS algorithm hard to realize and accurate phase analysis difficult to conduct. Here, we present a hybrid reconstruction algorithm, combining Fresnel reconstruction in spatial domain with the AS algorithm in frequency domain, to solve aliasing by spatial filtering. Through simulation, we demonstrate the feasibility and superiority of the hybrid algorithm and verified the precision (10−3 rad) of the hybrid algorithm with spectrum aliasing. We extract phase distributions from normal urothelial and bladder cancer tissues by the hybrid algorithm and make quantitative analysis through histogram and standard deviation. The result shows the hybrid algorithm in off-axis DH has great advantage for the high-precision phase extraction of tissues and supplies significant information for cancer diagnosis.

We investigated the propagation and autofocusing properties of three Airy-related beams, which are generated by three holograms with unique conjugation and symmetry. Beam patterns are simulated by using angular spectrum formalism and observed experimentally. The autofocusing behavior of black Airy beam is accompanied by formation of eight intensity peaks in the transversal plane. We find that the effect of non-ideal boundary condition is reflected in the diffraction fringes, and the affected ranges are different for different beams.

In-line lensless holography is considered with a random phase modulation at the object plane. The forward wavefront propagation is modelled using the Fourier transform with the angular spectrum transfer function. The multiple intensities (holograms) recorded by the sensor are random due to the random phase modulation and noisy with Poissonian noise distribution. It is shown by computational experiments that high-accuracy reconstructions can be achieved with resolution going up to the two thirds of the wavelength. With respect to the sensor pixel size it is a super-resolution with a factor of 32. The algorithm designed for optimal superresolution phase/amplitude reconstruction from Poissonian data is based on the general methodology developed for phase retrieval with a pixel-wise resolution in V. Katkovnik, ”Phase retrieval from noisy data based on sparse approximation of object phase and amplitude”, http://www.cs.tut.fi/~lasip/DDT/index3.html.

The Digital Holographic Microscopy in Transmission technique (DHM) is considered a useful tool in the noninvasive quantifying of transparent biological objects like living cells. In this work, we propose this technique to study and to monitor control macrophages infected by Leishmania (mouse lineJ774.A1). When the promastigotes enter in contact with healthy macrophages, they got phagocytosed and latterly confined in the formed parasitophorous vacuole. These processes change the morphology and density of the host macrophage. Both parameters can be measured in a label-free analysis of cells with the aid of the DHM technique. Our technique begins with the optical record of the holograms using a modified Mach-Zehnder interferometer and the reconstruction of the complex optical field transmitted by macrophages. In the latter point, we employ the angular spectrum algorithm. With the complex optical field reconstruction, we compute the field amplitude and the phase difference maps, which leads to describe one morphological characterization for the samples. Using phase difference maps is possible to measure internal variations for the integral refractive index, estimating the infection level of macrophages. Through the changes in the integral refractive index, it is also possible to describe and quantify in two different states the evolution of the infection. With these results some parameters of cells have been quantified, making the DHM technique a viable tool for diagnosis of biological samples under the presence of some pathogen.

Irradiating thin foils with very intense laser pulses results in the emission of swift ion bunches. These laser-accelerated ions exhibit properties that substantially differ from conventionally accelerated particles. A large number of a variety of ion species distributed over a broad energy and angular spectrum are confined to very short bunch durations and are sought to enable novel applications [1]. For many years these properties have been studied and optimized mainly by investigating the interaction process of intense lasers pulses with plasmas in exemplary experiments [2].

Terahertz radiation lies between the microwave and infrared regions in the electromagnetic spectrum. Emitted frequencies range from 0.1 to 10 THz with corresponding wavelengths ranging from 30 μm to 3 mm. In this paper, a continuous-wave Terahertz off-axis digital holographic system is described. A Gaussian fitting method and image normalisation techniques were employed on the recorded hologram to improve the image resolution. A synthesised contrast enhanced hologram is then digitally constructed. Numerical reconstruction is achieved using the angular spectrum method of the filtered off-axis hologram. A sparsity based compression technique is introduced before numerical data reconstruction in order to reduce the dataset required for hologram reconstruction. Results prove that a tiny amount of sparse dataset is sufficient in order to reconstruct the hologram with good image quality.

One-shot digital holographic imaging has the advantages of high stability and low temporal cost. However, its reconstruction is degraded severely by the laser speckle. A rectangle, ellipse, and diamond resampling mask method in spatial domain for speckle reduction is proposed. The effectiveness of the method for speckle reduction is explained successfully. In the method, one hologram recorded in a certain size is divided into N=S×T sub-holograms. Angular spectrum transform is applied to the holographic reconstruction of a diffuse object. N reconstructed amplitude images are calculated from the corresponding sub-holograms. Benefitting from speckle's random distribution, superimposing these N uncorrelated amplitude images would lead to a final reconstructed image with reduced speckle. Normalized relative standard deviation values of the reconstructed image are in good agreement with the asymptotical law. The maximum relative errors between the experiment data and the theoretical values are below 7.2%. The effect of the method on the spatial resolution of the reconstructed image is also quantitatively evaluated. Experimental and simulation results prove the feasibility and effectiveness of the proposed method.

Controllable manipulation of propagating surface plasmon polaritons is critical in plasmonics and important for nanophotonic applications. Here, we demonstrate theoretically that graphene plasmons (GPs) can be unidirectionally excited in an Au-graphene composite structure by a linearly polarized optical wave at the wavelength of 10.2 µm. The unidirectional ratio can reach as large as 900 with the incidence angle at 37.7° off normal, which is obtained by the angular spectrum of GPs. Moreover, the physical mechanism behind the unidirectional excitation is revealed to be the interference between anti-symmetric and symmetric amplitude distributions of GPs, which are induced by the gold rod antenna under the normal and grazing illuminations, respectively.

Non-paraxial perturbation wave equations are solved for general astigmatic Gaussian beams for the first time, to the best of our knowledge, in the angular spectrum representation by taking into account generic boundary conditions. Expressions for second-order corrections are derived and exemplified with an optical cavity made of two cylindrical mirrors. Non-paraxial corrections can lead, depending on the choice of boundary conditions, to a transverse S-shaped beam mode, which has been qualitatively been observed in a highly divergent non-planar four-mirror cavity.

Regarding the test object surface as scattering plane,and using spherical wave as reference wave,with different wavelength illumination,reconstruction position of object plane wave field is studied by using Angular spectrum theory.The result shows that,when the physical meaning of the image is not considered,diffraction image center reconstruction with S-FFT(Single Fourier Transform) is corresponding to the frequency spectrum center of object wave field.Taking the S-FFT reconstruction image as a reference,the location of the object wave field spectrum can be well determined,then the reconstruction field of different wavelength can be accurate overlapped with adjustable magnification reconstruction Angular spectrum method.

A method for selective excitation of Ince-Gaussian modes is presented. The method is based on the spatial distributions of Ince-Gaussian modes as well as the transverse mode selection theory. Significant diffraction loss is introduced in a resonator by using opaque lines at zero-intensity positions, and this loss allows to excite a specific mode; we call this method “loss control.” We study the method by means of numerical simulation of a half-symmetric laser resonator. The simulated field is represented by angular spectrum of the plane waves representation, and its changes are calculated by the two-dimensional fast Fourier transform algorithm when it passes through the optical elements and propagates back and forth in the resonator. The output lasing modes of our method have an overlap of over 90 % with the target Ince-Gaussian modes. The method will be beneficial to the further study of properties and potential applications of Ince-Gaussian modes.

In this paper, we derive analytical expressions to compute the covariance matrix of the signals impinging on a reconfigurable antenna array. We consider a receiver equipped with a linear antenna array where each antenna element can be independently configured to create a directive radiation pattern toward a selected direction. In our derivation, we assume a multimodal truncated Laplacian distribution to model the power angular spectrum (PAS) of the signals arriving at the array. Using the derived expressions, we are able to evaluate the correlation between the received signals as a function of the signal spatial distribution, the antenna array topology, and the radiation pattern characteristics of each element in the array. We also study the capacity of a reconfigurable multiple-input multiple-output (RE-MIMO) system and illustrate its relation to radiation pattern configurations and characteristics. We demonstrate how the derived expressions can be used to efficiently choose the configuration for each reconfigurable antenna element in the array that leads to an optimal compromise between low receive correlation and high receive power in order to maximize the link capacity. Simulation results are provided to validate our analytical expressions.

We consider a new family of nonparaxial diffraction-free laser beams with their complex amplitude being proportional to the n-th order Lommel function of two variables. Therefore, these beams are called Lommel beams (L-beams). We obtained explicit analytical expressions for the angular spectrum of plane waves and for the orbital angular momentum of the L-beams. Transverse intensity of the L-beams has a reflective symmetry with respect to both Cartesian coordinate axes. Since transverse intensity distribution of L-beams does not change upon propagation, L-beams are modes of free space (L-modes). Functions of complex amplitudes of even (n = 2p) and odd (n = 2p + 1) L-modes are mutually orthogonal. For certain parameter, L-modes become traditional Bessel modes.

Advantages and disadvantages of the non-approximated numerical implementation of the Rayleigh-Sommerfeld diffraction integral (RSD) are revisited. In this work, it is shown that as trade-off for its large computation load, the non-approximated RSD removes any limitation on the propagation range and does not introduce any artifact in the computed wave field. A non-approximated GPU implementation of the RSD is contrasted with the angular spectrum, the Fresnel transform, and a fast Fourier transform implementation of the RSD. The forecasted phase shift introduced in the propagated wave fields as light is diffracted on complementary apertures and utilized as a metric to quantify the performance of the tested methods. An application to numerical reconstructions with arbitrary shape and size of digital recorded holograms from digital lensless holographic microscopy is presented.

We performed an illumination simulation, wave-optical simulation, and experiment on a zoom homogenizer and conventional beam homogenizer. The wave-optical simulation was performed for each lenslet using the shifted angular spectrum method for effective memory use. In the experiment, the parameters of the zoom homogenizer and beam homogenizer at all zoom positions were set using a system matrix. The uniformity and peak effect of the beam homogenizer were 16.57% and 16.63%, respectively, but those of the zoom homogenizer were 7.15% and 1.46%, respectively. The illumination field generated by the zoom homogenizer had a higher uniformity and lower peak effect at all zoom positions than the conventional one.

Digital holography records the entire wavefront of an object, including amplitude and phase. To reconstruct the object numerically, we can backpropagate the hologram with Fresnel–Kirchhoff integral-based algorithms such as the angular spectrum method and the convolution method. Although effective, these techniques require prior knowledge, such as the object distance, the incident angle between the two beams, and the source wavelength. Undesirable zero-order and twin images have to be removed by an additional filtering operation, which is usually manual and consumes more time in off-axis configuration. In addition, for phase imaging, the phase aberration has to be compensated, and subsequently an unwrapping step is needed to recover the true object thickness. The former either requires additional hardware or strong assumptions, whereas the phase unwrapping algorithms are often sensitive to noise and distortion. Furthermore, for a multisectional object, an all-in-focus image and depth map are desired for many applications, but current approaches tend to be computationally demanding. We propose an end-to-end deep learning framework, called a holographic reconstruction network, to tackle these holographic reconstruction problems. Through this data-driven approach, we show that it is possible to reconstruct a noise-free image that does not require any prior knowledge and can handle phase imaging as well as depth map generation.

Contactless ultrasonic acoustic energy transfer (UAET) is a new technology that eliminates risks or impracticalities associated with wired electrical connections or batteries that need to be replaced on a regular basis. This technology, which is based on the reception of acoustic waves at ultrasonic frequencies by piezoelectric receivers, can be used to wirelessly charge low-power electronics. The execution and efficiency of this technology can be significantly enhanced through patterning and focusing of the transmitted acoustic energy in space to simultaneously power distributed sensors or devices. This work investigates the use of an acoustic hologram to create a multifocal pressure pattern in a plane where target receivers are located at specific focal points or regions. First, a phase-shifting hologram is designed using an iterative angular spectrum approach. Then, a multi-physics acoustic-electro-elastic model is presented for an axially vibrating cylindrical transmitter used to power multiple piezoelectric receivers, in conjunction with the hologram. Experiments are also performed to show the capability of an acoustic hologram to selectively power an array of the receivers. Both analytical and experimental results show a dramatic enhancement of power transfer to receivers exposed to a multi-focal pressure pattern created by the hologram. As a case study, a bi-focal receiver setup is investigated where one receiver is targeted. The UAET simulation predicts a doubling of the power transfer to the targeted receiver, which is verified by the proof-of-concept experiment. The effects of system parameters such as input frequency and hologram aperture size are also reported.

With the development of microfabrication technology, it has become possible to modulate the optical wavefront with high accuracy by a device such as a liquid crystal spatial light modulator (SLM). In this study, we conducted a theoretical analysis and experimental study on the generation of Laguerre Gaussian beam of vortex light wave using phase modulation SLM. Numerical simulation and experimental results on the generation of Laguerre Gaussian beam by both binary and phase only modulation are discussed based on the angular spectrum method and the Fresnel transformation method in hologram (CGH) diffraction. The experimental results show that Fresnel diffraction calculation based on Fourier transform method can simulate the light diffraction of SLM very well. This method is very suitable for the action simulation of digital optical wavefront control devices such as SLM. It can be imagined that the simulation method in this study can also play an important role in the design and development of digital optical diffraction elements.

A resampling ring-mask method in spatial spectral domain (RRM-SSD) is proposed for speckle reduction in one-shot digital holography. Spatial spectrum of a hologram with speckle is divided into several subspectra using the resampling ring masks. Different subspectra are individually used to obtain the corresponding reconstructed amplitude images by the angular spectrum method. With the random distribution of the speckle, averaging these uncorrelated amplitude images would successfully enable speckle-reduced reconstruction. No specific operations for hologram recording or complex process for reconstruction are required in this method. Comparison with the previous rectangular mask method in spatial domain proves the advantage of the RRM-SSD method for both speckle reduction and high-resolution reconstruction. Experimental results show that the RRM-SSD method is efficient and simple for speckle reduction, which can be widely used in holographic imaging.

Phase-shifting microwave holography utilizes the antennas to record the hologram. In this technique, the antenna has to perform two-dimensional (2-D) scanning over the test area corresponding to each phase shift in the reference wave. A numerical three-step phase-shifting is proposed for recording the microwave holograms in which only a single 2-D scan over an area is recorded experimentally whereas two remaining phase shifts are introduced numerically. This method is applied for imaging of metallic objects to inspect the feasibility of the proposed method. The qualitative results exhibit its effectiveness while reconstructing the amplitude and phase of an object at a microwave frequency of 8.5 GHz (or λ = 35.29 mm).

Development of digital holography opened new ways of both transparent and opaque objects non-destructive study. In this paper, a digital hologram reconstruction process is investigated. The advantages and limitations of common wave propagation methods are discussed. The details of a software implementation of a digital hologram reconstruction methods are presented. Finally, the performance of each wave propagation method is evaluated, and recommendations about possible use cases for each of them are given.

Quantitative and reproducible air-coupled ultrasound (ACU) testing requires characterization of the volumetric pressure fields radiated by ACU probes. In this paper, a closed-form reradiation method combining the Rayleigh–Sommerfeld integral and time-reversal acoustics is proposed, which allows calculation of both near- field and far-field based on a single-plane measurement. The method was validated for both 3-D (circular, square) and 2-D (rectangular) planar transducers in the 50–230 kHz range. The pressure fields were scanned with a calibrated microphone. The measurement window was at least four times the size of the transducer area and the grid step size was one third of the wavelength. Best results were observed by acquiring the measurement plane at near-field distance. The method accurately reproduces pulsed ultrasound waveforms and pressure distributions (RMSE

International audience; Modern holography for 3D imaging allows to reconstruct all the parallaxes that are needed for a truly immersive visualisation. Nevertheless, it represents a huge amount of data which induces higher transmission and storage requirements. To gain more popularity and acceptance, digital holography demands development of efficient coding schemes that provide significant data compression at low computation cost. Another issue that needs to be tackled when designing holography coding algorithms is interoperability with commonly used formats. The upcoming JPEG Pleno standard aims to develop a standard framework for the representation and exchange of new imaging modalities, such as holographic imaging, while maintaining backward compatibility with legacy JPEG decoders. This paper presents a lossy compression method for holographic images that exhibits good coding performance while considering the computation cost and backward compatibility with legacy JPEG standard. To validate our findings, the results of our tests are shown and interpreted.

An angular spectrum holographic algorithm is proposed for generating three-dimensional (3D) reconstruction from multiple computational tomography (CT) slices. Objects consist of multiple slices can be easily modeled by the angular spectrum. So the 3D structure can be built through the superposition of computer generated phase holograms originally from parallel discrete planes at different depths. Then the superposed phase hologram is uploaded to the phase-only spatial light modulator (SLM). With the SLM illuminated by the coherent light, the 3D reconstruction is observed by a camera. The proposed method is more computationally efficient compared with the point source algorithm, and the angular spectrum holographic algorithm can process more large-capacity CT data for the 3D visualization. Experiment demonstrates the feasibility of reconstructing CT biological structure with holographic display.

A rapid autofocusing technique is a fundamental element for a vast range of applications of digital holography. In this paper we propose a new autofocusing method that permits to detect a tilted optimal focus plane. The method is based on estimation of focusing condition of the optical field by evaluating the sharpness in its amplitude distribution. The developed algorithm is fully automated. It consists of two major steps, first the rotation axis is localized from the map of local sharpness and then the angular orientation of the image plane is derived by maximizing the focus of optical fields reconstructed in many subsequent tilted planes. In our study six image sharpness quantification methods are investigated and the numerical propagation between inclined planes is performed with an efficient band limited angular spectrum algorithm. The utility of the proposed method for autofocusing to a tilted image plane is experimentally confirmed in a digital holographic microscopy setup by carrying out a successful reconstruction of holograms of the exemplary amplitude (the 1951 USAF positive target) and phase (a matrix of microlenses) objects.

Terahertz (THz) continuous-wave digital holography is an advanced interference imaging technique that can reconstruct quantitative distributions of amplitude and phase of the sample in real time with high resolution. In this paper, a reflective off-axis holographic system is presented. A Gaussian fitting method is applied to enhance the hologram contrast and Laplacian of Gaussian filter is used to obtain the reconstructed distance automatically. Furthermore, spectrum filtering method and angular spectrum algorithm are used to obtain the complex amplitude of the one-yuan chinese metal coin. The results confirm the prospective application of terahertz digital holography in the surface morphology for reflective samples.

In order to measure the three-dimensional microstructure of surface defects on optical component, a novel measuring method based on digital image-plane holographic microscopy (DIPHM) is proposed in this paper. The experimental system has been designed and built to measure the microstructure of optical component’s surface defects. The object light wavefront can be reconstructed by using the algorithm based on the angular spectrum theory, and the technique of phase correction is contributive to eliminate the system error. There is a definite relationship between the object light wavefront and the surface topography, so the 3D microstructure of surface defects can be measured. This measuring technique is helpful to judge the damage degree of the optical component and analysis the influence of the surface defects, and it is of great significance to ensure the laser system security running.

Theoretical model is built up to investigate earth-satellite laser communication numerically, where atmosphere affects the communication effect greatly. The distribution of atmosphere refractivity and turbulence are two main aspects in atmosphere's influence on earth-satellite laser links. Simulation based on angular spectrum theory is performed to study laser propagation through atmosphere to outer space, and different distribution of atmosphere refractivity is discussed. Then the astronomical refraction errors introduced by atmosphere refractivity are investigated. At last, the influence of turbulence on laser patterns and propagation angles are discussed.

A terahertz (THz) digital holography system is built using a Gunn oscillator worked at 0.17 THz as the source and a Pyroelectric array camera as the detector array. Image was reconstructed in frequency domain of the hologram by using rectangular windowed filter and angular spectrum theorem was used to restore the complex amplitude of object wave.

Graphene is a 2-D sheet of carbon atoms arranged in a honeycomb lattice, its atomic thickness limits its interaction with light [1], then some hybrid plasmonic metal-graphene systems were proposed for converting incident light into propagating GPs and controlling their propagation and focusing to enhance light-matter interactions [2–4], which has become a research hot-spot due to the combination of several appealing properties in recent years. However, hardly any systems were proposed for unidirectional GPs launching, in this paper, In this paper, we demonstrate theoretically that unidirectional graphene plasmons (GPs) can be excited on the Au-graphene composite structure with an oblique illumination. Angular spectrum is used to simply justify the unidirectional efficiency, the ratio can reach about 50 dB with incident angle at 41° off normal in our simulation. The effects with different substrate are also described in our work. Based on our theoretical analysis, we show that the principle behind the unidirectional GPs mechanism is based on the polarity of the surface charges distribution on the boundary of Au, which launching anti-symmetrically or symmetrically GPs mode with normal or grazing incidence plane wave. We stress that this configuration is feasible in experiment.

Digital Holography Microscopy (DHM) is a powerful tool for three-dimensional imaging of micro-objects, since it yields an intensity image, called hologram. This is interference pattern, records the intensity information and allow reconstruction of the phase shift introduced by objects. With the development of computer and fast Fourier transformation technology, DHM has been widely used in biological and material tissues, etc.. In this paper, DHM is used to measure the abrupt edges and surface of reflect objects which are calibrated. Phase compensation uses the physical configuration to compensate the phase aberration, such as Microscope Objective (MO), spherical aberration and other curvature introduced by specimen or instruments in set-up. We apply this method to obtain the pure holograms of objects. The holograms produce more accurate phase-contrast imaging and three-dimensional imaging. Angular Spectrum Propagation (ASP) approach is a strict diffraction integration, and widely used for many applications, such as short-distance propagation, and the off-axis system and tilted plane. Here, we achieve numerical reconstruction of the hologram with ASP under phase compensation condition in an off-axis system.First, we use the fast Fourier transformation for the hologram and get the frequency image. Then, filter out the spectrum about the image which we need. Finally, inverse Fourier transform of the filtered spectrum and get the complex amplitude information. The phase image and intensity image of specimen is obtained after calculating the reconstruction distance.

Variable light focusing is the ability to flexibly select the focal distance of a lens. This feature presents technical challenges, but is significant for optical interrogation of three-dimensional objects. Numerous lens designs have been proposed to provide flexible light focusing, including zoom, fluid, and liquid-crystal lenses. Although these lenses are useful for macroscale applications, they have limited utility in micron-scale applications due to restricted modulation range and exacting requirements for fabrication and control. Here, we present a holographic focusing method that enables variable light focusing without any physical modification to the lens element. In this method, a scattering layer couples low-angle (transverse wave vector) components into a full angular spectrum, and a digital optical phase conjugation (DOPC) system characterizes and plays back the wavefront that focuses through the scattering layer. We demonstrate micron-scale light focusing and patterning over a wide range of focal distances of 22-51 mm. The interferometric nature of the focusing scheme also enables an aberration-free scattering lens. The proposed method provides a unique variable focusing capability for imaging thick specimens or selective photoactivation of neuronal networks.

We propose and theoretically demonstrate a novel optical fiber with an annular arrayed-waveguide to implement Airy phase and amplitude modulation, and generate an abruptly autofocusing circular Airy beam. The properties of wave propagation in Airy fiber and free space are studied by using the coupled-mode theory and angular spectrum method. The calculated results show that the output beam from such a fiber has a circular Airy-like pattern and can autofocus with the intensity maxima following a parabolic trajectory. We also show that the position of the focus point of the output beam from the Airy fiber can be easily controlled by changing input wavelength.

An Off-axis Fresnel interferometric imager was constructed to acquire holograms using a highly coherent, narrowband, continuous wave source tunable over 0.3 – 1.0 THz. Fresnel and angular spectrum reconstruction methods of amplitude and phase holograms are presented and compared. While transverse resolution was on the order of the wavelength, unprecedented depth resolution of nearly λ/300 (2 µm) is reported.

Optical-tweezers experiments in molecular and cell biology often take place near the surface of the microscope slide that defines the bottom of the sample chamber. There, as elsewhere, force measurements require force-calibrated tweezers. In bulk, one can calculate the tweezers force from first principles, as recently demonstrated. Near the surface of the microscope slide, this absolute calibration method fails because it does not account for reverberations from the slide of the laser beam scattered by the trapped microsphere. Nor does it account for evanescent waves arising from total internal reflection of wide-angle components of the strongly focused beam. In the present work we account for both of these phenomena. We employ Weyl's angular spectrum representation of spherical waves in terms of real and complex rays and derive a fast-converging recursive series of multiple reflections that describes the reverberations, including also evanescent waves. Numerical simulations for typical setup parameters evaluate these effects on the optical force and trap stiffness, with emphasis on axial trapping. Results are in good agreement with available experimental data. Thus, absolute calibration now applies to all situations encountered in practice.

Advancements and reviews of imaging and instrumentation applications of optical vortices will be described. Applications include astronomy (coronagraphy for exoplanet imaging), radiation protection (PSF engineering for laser suppression), scatterometry (complete angular spectrum measurements for particle sizing), and methods of determining the degree of spatial coherence. An optical vortex phase element may be placed in a pupil plane or focal plane to benefit from the Fourier transform properties of the “twisted light”. Advanced optical devices may benefit from the additional use of deconvolution schemes to augment the spatial filtering properties of vortex-modified beams. Furthermore, Gerschberg-Saxon type iterative algorithms also provide a means to design higher order phase elements for imaging applications of complex light.

Random-sampled wavefront recording plane for fast computer generated hologram is proposed. This approach can accelerate computing process by replacing nonuniform sampled angular spectrum method to ray-tracing method in wavefront recording plane.

An off-axis holographic microscope, in a transmission mode, calibrated to automatically detect the presence of Trypanosoma cruzi in blood is developed as an alternative diagnosis tool for Chagas disease. Movements of the microorganisms are detected by measuring the phase shift they produce on the transmitted wave front. A thin layer of blood infected by Trypanosoma cruzi parasites is examined in the holographic microscope, the images of the visual field being registered with a CCD camera. Two consecutive holograms of the same visual field are subtracted point by point and a phase contrast image of the resulting hologram is reconstructed by means of the angular spectrum propagation algorithm. This method enables the measurement of phase distributions corresponding to temporal differences between digital holograms in order to detect whether parasites are present or not. Experimental results obtained using this technique show that it is an efficient alternative that can be incorporated successfully as a part of a fully automatic system for detection and counting of this type of microorganisms.

International audience; An holographic microscopy reconstruction method compatible with high numerical aperture microscope objective (MO) up to NA=1.4 is proposed. After off axis and reference field curvature corrections, and after selection of the +1 grating order holographic image, a phase mask that transforms the optical elements of the holographic setup into an afocal device is applied in the camera plane. The reconstruction is then made by the angular spectrum method. The field is first propagated in the image half space from the camera to the afocal image of the MO optimal plane (plane for which MO has been designed) by using a quadratic kernel. The field is then propagated from the MO optimal plane to the object with the exact kernel. Calibration of the reconstruction is made by imaging a calibrated object like an USAF resolution target for different positions along z. Once the calibration is done, the reconstruction can be made with an object located in any plane z. The reconstruction method has been validated experimentally with an USAF target imaged with a NA=1.4 microscope objective. Near-optimal resolution is obtained over an extended range (±50 µm) of z locations.

We use numerical simulation and optimization algorithms to apply optical proximity correction (OPC) to different mask structures for exposure on a Mask Aligner in proximity mode. The range of OPC solutions reaches from subtle changes in the mask layout to masks that have lost almost all resemblance to the structure to be printed. An extreme case is the printing of periodic structures where we make use of the image reversal caused by the Talbot effect. We also show the improvement that can be obtained when co-optimizing the angular spectrum of the illumination, i.e. when performing a source-mask optimization (SMO).

We propose an approach based on axial translation of a charge-coupled device (CCD) and gradient operator method for numerical reconstruction in in-line digital holography. The object wave in the hologram (or CCD) plane is determined using one position translation of CCD, and a phase-shifting device can be fully avoided. Gradient operator method is further applied to detect the focal plane of an object, and the object wave is reconstructed by an angular spectrum algorithm with the detected focal distance. The feasibility and effectiveness of the proposed method are demonstrated by numerical simulations.

In this paper, we propose an extremely broadband Rayleigh resonant reflector with sharp angular spectra operating in near infrared wavelength band, this device consisting of a single germanium resonant grating layer is designed and analyzed by using with the rigorous vector diffraction theory. At the Rayleigh angle, the first diffracted order can be appear from evanescent to a propagating one, thus, a very sharp angular spectrum characteristics can be presented in the device. Based on the guided mode resonant effect, high index material such as silicon and germanium can be designed as wide band reflector, beam splitter and polarizer in near infrared wavelength region. Through connecting Rayleigh phenomena and guided mode resonant effect, we can design a new kind of optical devices with versatile characteristics such as sharp angular spectra and extremely wide reflection band. In this paper, we present a Rayleigh resonant reflector with extremely high reflection ( R > 99.5%) for TE polarization light over ∼600 nm wavelength range and sharp angular spectral distribution. In addition, it is shown from our calculations that the high-index nano-layer located adjacent to the substrate is seen to critically affect the resulting spectra of Rayleigh resonant reflector.

A recent method has been proposed for determining the optimal radiation characteristics of antennas that maximize the diversity gain for a given antenna aperture and power angular spectrum of the incident field. However, because this approach results in antennas whose current distributions overlap in the aperture, it is difficult to achieve the radiation characteristics using practical designs. This paper proposes several methods that construct the near-optimal radiation characteristics assuming the apertures representing distinct antennas are disjoint. Computational results show that the average diversity performance achieved for these approximate radiation characteristics is roughly 1.3 dB below that achieved using the optimal patterns.

We propose an optical see-through holographic near-eye-display that can control the depth of field of individual virtual three-dimensional image and replicate the eyebox with dynamic steering. For optical see-through capability and eyebox duplication, a holographic optical element is used as an optical combiner where it functions as multiplexed tilted concave mirrors forming multiple copies of the eyebox. For depth of field control and eyebox steering, computer generated holograms of three-dimensional objects are synthesized with different ranges of angular spectrum. In optical experiment, it has been confirmed that the proposed system can present always-focused images with large depth of field and three-dimensional images at different distances with shallow depth of field at the same time without any time-multiplexing.

Digital holography is a very effective tool for three- dimensional imaging of objects, since it yields the phase information directly without the need for additional optics. Another advantage is that of numerical focusing, allowing one to focus on to any desired plane. It has been used for microscopy with high effectiveness. One of the important features of digital holographic microscopy (DHM) is that it can be used for phase contrast imaging of otherwise transparent objects. This aspect of DHM is utilized here to study the dynamics of phase objects. Angular spectrum propagation (ASP) approach to scalar diffraction theory is used for numerical reconstruction of holograms.

The negative ion accelerators that produce the high-energy particle beams for the neutral injection systems for the International Tokamak Experimental Reactor (ITER) also produce unwanted particles such as electrons. These electrons are emitted in a wide angular spectrum that allows some of them to directly intercept sensitive beamline components such as the cryogenic pumps. As the electrons are also subject to backscattering, indirect interception always occurs. In this article the electron spectra produced by the Heating Neutral Beam (HNB) and Diagnostic Neutral Beam (DNB) accelerators are calculated. It is shown that these are very different. It is proposed to install electron dumps in the beamlines to intercept electron power directed towards inconvenient places in the HNB and DNB beamlines.

To experimentally demonstrate the subwavelength focusing of depth-tuned or non-depth-tuned plasmonic lenses, we first designed this type of lens using diffraction-coupling-angle based method, then fabricated the structure in gold thin film with focused ion beam, and finally characterized its focusing behavior using near-field scanning optical microscope. It is found that this type of lens has a resolution limit on the focal plane due to the field represented by angular spectrum having a cut-off frequency, while at the near field the lens has sub-diffraction limit focusing capability due to the existence of high-angular-frequency components in the field.

Based on numerical simulations, we show the influence of the illumination on process windows in mask aligner lithography. The precise shaping of the illuminating light can lead to greatly increased process windows. We show that the best results are obtained when combining an optimized illumination with optimized mask structures and Optical Proximity Correction (OPC). We model the illumination according to the novel illumination system for SUSS MicroTec mask aligners, referred to as MO Exposure Optics, which allows a precise shaping of the angular spectrum and the partial coherence of the mask illuminating light by using Illumination Filter Plates (IFPs).