Reference Wave Research Articles

Analysis of three-dimensional mapping problems in incoherent digital holography.

Self-interference digital holography (SIDH) and Fresnel incoherent correlation holography (FINCH) are recently introduced holographic imaging schemes to record and reconstruct three-dimensional (3-D) information of objects by using incoherent light. Unlike conventional holography, a reference wave in incoherent holography is not predetermined by an experimental setup, but changes with target objects in incoherent holography. This makes the relation between the 3-D position information of an object and those stored in a measured hologram quite complicated. In this paper, we provide simple analytic equations for an effective 3D mapping between object space and the image space in incoherent holography. We have validated our proposed method with numerical simulations and off-axis SIDH experiments.

Dynamic quantum state holography

We present a pulse-shaper-based holographic technique for the time-resolved and phase-sensitive observation of ultrafast quantum dynamics. The technique combines bichromatic white light polarization pulse shaping with the tomographic reconstruction of photoelectron wave packets. The physical scheme is based on the interference of a probe wave packet from $N+1$ resonance-enhanced multiphoton ionization via the target states and a reference wave packet from $M+1$ multiphoton ionization of the ground state. To create the wave packets, we employ carrier-envelope phase stable bichromatic ($M\ensuremath{\omega}$:$N\ensuremath{\omega}$) pump-probe pulse sequences. The scheme is demonstrated on femtosecond Rydberg wave-packet dynamics in potassium atoms using corotating circularly polarized ($2\ensuremath{\omega}$:$3\ensuremath{\omega}$) pulse sequences. The interference of continuum states with different angular momenta yields a crescent-shaped photoelectron wave packet rotating in the laser polarization plane due to the interplay of the optical phase and the accumulated quantum phase. Carrier-envelope phase control of the rotation provides access to the photoelectron asymmetry, enabling background-free detection of the crescent's angular motion which maps the bound-electron dynamics.

High-Resolution Hologram Calculation Method Based on Light Field Image Rendering

A fast calculation method for a full parallax high-resolution hologram is proposed based on elemental light field image (EI) rendering. A 3D object located near the holographic plane is firstly rendered as multiple EIs with a pinhole array. Each EI is interpolated and multiplied by a divergent sphere wave and interfered with a reference wave to form a hogel. Parallel acceleration is used to calculate the high-resolution hologram because the calculation of each hogel is independent. A high-resolution hologram with the resolution of 200,000 × 200,000 pixels is calculated within only eight minutes. Full parallax high-resolution 3D displays are realized by optical reconstructions.

Phase-shifting digital holography with a tri-focal Fibonacci telescope in a single exposure

In this work a tri-focal Fibonacci telescope based on a Greek-ladder photon sieve was constructed to realize three isometric images at the same time. Two of these interfere with the plane reference wave to form two frames of a phase-shifting hologram and the last unused one is referred to as the object intensity. Two-step phase-shifting interferometry can be used to reconstruct the test object in a single exposure. Simulations and experiments were carried out which verified the effectiveness of our proposed method. With advantage of real-time phase and a light-weight diffractive lens, the tri-focal sieve can be applied in bio-microscopy, surface testing and so on.

Геометрооптический механизм восстановления волнового фронта

The mechanism of wavefront reconstruction by a geometric-optical reflection of reconstructing light from surfaces with constant phase differences between the object and reference waves used to record the interference fringe structure in the medium bulk is analyzed. This mechanism is compared with the holographic one. Experiments in volume medium and in planar optical waveguide were carried out. Several types of achromatic optical elements are proposed. The optoacoustic focusing element, which can create a great local stress in a special shaped area inside the matter, is discussed. The possibility of the ultrashort pulse temporal reconstruction is demonstrated.

Multi-reference lens-less Fourier-transform holography with a Greek-ladder sieve array

Lens-less Fourier-transform holography has been actively studied because of its simple optical structure and its single-shot recording. However, a low-contrast interferogram between the reference and object waves limits its signal to noise ratio. Here, multi-reference lens-less Fourier-transform holography with a Greek-ladder sieve array is proposed in the experiment and demonstrated effectively to improve the signal to noise ratio. The key technique in our proposed method is a Greek-ladder sieve array, which acts as not only a wave-front modulator but also a beam splitter. With advantages of the common path, single shot, and no need for a lens, this system has enormous potential in imaging and especially in extreme ultraviolet and soft X-ray holography.

Resolution Analysis in a Lens-Free On-Chip Digital Holographic Microscope

Lens-free on-chip digital holographic microscopy (LFOCDHM) is a modern imaging technique whereby the sample is placed directly onto or very close to the digital sensor, and illuminated by a partially coherent source located far above it. The scattered object wave interferes with the reference (unscattered) wave at the plane where a digital sensor is situated, producing a digital hologram that can be processed in several ways to extract and numerically reconstruct an in-focus image using the back propagation algorithm. Without requiring any lenses and other intermediate optical components, the LFOCDHM has unique advantages of offering a large effective numerical aperture (NA) close to unity across the native wide field-of-view (FOV) of the imaging sensor in a cost-effective and compact design. However, unlike conventional coherent diffraction limited imaging systems, where the limiting aperture is used to define the system performance, typical lens-free microscopes only produce compromised imaging resolution that far below the ideal coherent diffraction limit. At least five major factors may contribute to this limitation, namely, the sample-to-sensor distance, spatial and temporal coherence of the illumination, finite size of the equally spaced sensor pixels, and finite extent of the image sub-FOV used for the reconstruction, which have not been systematically and rigorously explored until now. In this work, we derive five transfer function models that account for all these physical effects and interactions of these models on the imaging resolution of LFOCDHM. We also examine how our theoretical models can be utilized to optimize the optical design or predict the theoretical resolution limit of a given LFOCDHM system. We present a series of simulations and experiments to confirm the validity of our theoretical models.

Technique of detecting optical components based on coherent modulation imaging

As one of the coherent diffractive imaging (CDI) techniques, coherent modulation imaging (CMI) is a lensless phase imaging technology with diffraction limited resolution in theory. Unlike multiple measurement phase retrieval algorithms, the CMI can achieve fast convergence speed with single-shot measurement by introducing a pre-characterized random phase modulator. Besides, it has simple structure without reference wave based on iterative engine. Despite the fact that the matured phase imaging can be used to implement the on-line wave diagnostics of laser pulse, in this work we accurately measure the face-type of optical component with peak-to-valley value below 0.5<i>λ</i> (<i>λ</i> = 632.8 nm) by using the CMI for the first time. In order to verify its measurement capability, 10 quartz windows with a diameter of 80 mm and PV value between 0.1<i>λ</i> and 0.5<i>λ</i> are repeatedly measured. Compared with the results of commercial interferometer, the root mean square error (Root MSE) of the peak-to-valley (PV) ratio of the results of the CMI is 0.0305<i>λ</i>, and the Root MSE of the root mean square (RMS) is 0.00522<i>λ.</i> The measurement accuracy of PV ratio and RMS can reach 0.1<i>λ</i> and 0.01<i>λ</i> respectively. In addition, the parallel flat with PV ratio = <i>λ</i>/20 is measured and analyzed with CMI, and its noise level is also analyzed. Considering that the potential improvement of CMI is available in the future, the CMI is expected to become a new technique for optical metrology with high precision, which is different from interferometry.

Specific Features of Spectral Properties of Volume Reflection Holograms of Diffuse Objects

Specific features of spectral properties of volume reflection holograms are determined, namely, broadening of the spectral response (reflex) contour toward both the short-wave and long-wave spectral ranges in the case where the angle of incidence of the white-light probing beam differs from the direction of reference wave propagation in hologram recording. This effect is essentially different from the known angular dependence of the reflex of the elementary volume reflection grating. A theoretical explanation for experimental data is provided, and formulas are derived, which are used to calculate the transmission spectra of the studied gratings. These spectra are found to be qualitatively consistent with the experiment.

Three-step electronic speckle pattern interferometry method with arbitrary phase shifts of reference wave

Three-step electronic speckle pattern interferometry method with arbitrary phase shifts of reference wave

Multireference configuration interaction and perturbation theory without reduced density matrices.

The computationally expensive evaluation and storage of high-rank reduced density matrices (RDMs) has been the bottleneck in the calculation of dynamic correlation for multireference wave functions in large active spaces. We present a stochastic formulation of multireference configuration interaction and perturbation theory that avoids the need for these expensive RDMs. The algorithm presented here is flexible enough to incorporate a wide variety of active space reference wave functions, including selected configuration interaction, matrix product states, and symmetry-projected Jastrow mean field wave functions. It enjoys the usual attractive features of Monte Carlo methods, such as embarrassing parallelizability and low memory costs. We find that the stochastic algorithm is already competitive with the deterministic algorithm for small active spaces, containing as few as 14 orbitals. We illustrate the utility of our stochastic formulation using benchmark applications.

Holographic Design of Beam-Switchable Leaky-Wave Antenna

A holographic design of beam-switchable leaky-wave antenna (LWA) is presented. The proposed design consists of a holographic impedance modulated surface (HIMS) and control circuit. In this design, the HIMS, which carries impedance characteristics of four beams, is obtained by using a modified modulation method in the same aperture. Thus, the proposed HIMS can generate four switchable beams at a fixed frequency when it is excited by different reference waves. By controlling p-i-n diodes inserted along the feedline, four working states can be obtained. The proposed LWA is fabricated and measured. Four switchable beams with pitch angles of θ 1 = θ 2 = −30°, θ 3 = θ 4 = 30° and azimuth angles of ϕ 1 = 0°, ϕ 2 = 90°, ϕ 3 = 180°, and ϕ 4 = 270° are obtained at 18 GHz. The measured peak gain of each beam is better than 17.2 dBi.

Early detection of cancerous tissues in human breast utilizing near field microwave holography

AbstractThis work demonstrates an application of near field indirect microwave holography for the detection of malignant tissues in human breast in an effective way. The holograms are recorded by two directive antennas aligned along each other's boresight while performing a raster scan over a 2D plane utilizing XY‐linear motorized translation stage and a uniform reference wave. The whole information that is, amplitude and phase of an object has been provided by indirect holography at microwave frequencies. The extracted phase values are used to determine the dielectric permittivity values which are further utilized for the identification and validating the positions of malignant tissues in the breast phantom. The experimental evaluations performed on the in‐house designed and developed tissue mimicking 3D printed breast phantoms. The experimental results demonstrate the ability of microwave holography using directive antennas in detecting and identifying the tumors upto the minimum size of 4 mm and maximum depth of 25 mm in fabricated phantom. The quantitative results present the potential of the Near Field Indirect Holographic Imaging (NFIHI) in order to develop an efficient and economical tool for breast cancer detection.

Numerical three-step phase-shifting microwave holography

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).

An Improved Phase-Shifted-Carrier Technique for Hybrid Modular Multilevel Converter With Boosted Modulation Index

The phase-shifted-carrier (PSC) technique is preferred for multilevel converters in medium-voltage applications with low submodule (SM) number. This technique can elevate the equivalent switching frequency resulting in low total harmonic distortions. However, for half-/full-bridge hybrid modular multilevel converter (MMC) with boosted modulation index, the conventional PSC method is invalid due to the asymmetric voltage reference wave. The SM capacitor voltages deviate from the rated value and harmonics below equivalent switching frequency appear in the arm and equivalent ac voltages. This paper introduces an improved PSC technique with a capacitor sorting algorithm to overcome this problem. The negative part of the reference wave is turned over and then multiplied by a correction factor. The angular displacement for triangular carriers between the upper and lower arms is determined by the parity of the half-bridge number per arm. With the proposed method, the capacitor voltages are balanced and the ac voltage of MMC has the lowest harmonic distortion. Double-Fourier analysis for the proposed technique is carried out, and harmonic characteristics are revealed. The experimental results validate the correctness and feasibility of the improved PSC technique for hybrid MMC with boosted modulation index and asymmetric reference wave.

Polarization-selective waveguide holography in the visible spectrum.

We propose and experimentally demonstrate a polarization-selective waveguide hologram at optical wavelengths, based on an all-dielectric metamaterial multilayer system. We show that two spatially separated or overlapped holographic images can be produced with two orthogonally polarized beams, incorporated into a binary computer generated hologram (CGH). These two images can be combined into a single 3D stereoscopic image observable using linearly or circularly polarized glasses. The two polarized beams can also be utilized to construct radially and azimuthally polarized "vortex" beams. The fundamental and first higher-order TM and TE modes of an optical waveguide are used to guide the two polarization states with distinct propagation constants. The two guided waves act as spatially distinct reference waves such that the integrated, on-chip hologram can distinguish the two and provide two independent images corresponding to the two polarizations. Polarization selective waveguide holograms can be used in a diverse set of applications, from chip-scale displays and augmented reality (AR) to optical trapping.

Fabrication and Study of a Concave Crystal Mirror for the KORTES Project

A method for fabrication of a concave spherical mirror made of crystalline quartz is proposed and X-ray optical properties of the mirror are studied. The radius of curvature is 1630 mm. The shape of the mirror surface is studied using an interferometer with a diffraction reference wave. In the entire processing region, the maximum deviation from the nearest sphere is about 0.2 μm and the rms is 34 nm, so that high quality of imaging is provided with an angular error of about 2″ (angular seconds). Reflection coefficient (about 7%) and lower bound limit of spectral selectivity (λ/δλ ≈ 1775) are determined in the vicinity of a wavelength of λ = 0.834 nm, which is close to the working wavelengths of the MgXII doublet (λ = 0.8418 and 0.8423 nm). Position of the Bragg peak and spectral selectivity remain unchanged upon bending of the crystal mirror within measurement accuracy.

Measurement Error of Interferometers with Diffraction Reference Wave

An experimental setup and results on aberration of sources of a reference spherical wave (SRSW) based on a single-mode optical fiber with a subwavelength output aperture obtained with the aid of an optical part of recording system (OPRS) are presented. SRSW and OPRS are developed for referenceless interferometer with diffraction reference wave. Methods for minimization of the measurement error are proposed. The SRSW and OPRS provide subnanometer measurement accuracy for optics. An increase in the measurement accuracy of the interferometer to a picometer level is discussed.

Single-shot phase-shifting image-plane digital holography with tri-focal Fibonacci-Billet split lens.

Phase-shifting holography has been widely applied in the field of non-destructive testing and interference imaging. Compared to the previous single-shot phase-shifting holography, here tri-focal Fibonacci-Billet split lens was introduced into Mach-Zehnder interferometer, in which the upper half of the Fibonacci-Billet split lens can realize three phase-locking copies of the planar reference wave and the lower half is used to generate three identical copies of object. The interference pattern is recorded by a detector in one single exposure. The test object can be reconstructed by three-step phase-shifting interferometry. The corresponding experiment is carried out to verify the effectiveness of this method. With advantages of real-time reconstruction and amplitude-only diffraction lens, it is very useful for fast imaging and optical element detection.

Color single-pixel digital holography with a phase-encoded reference wave.

We propose and demonstrate a multicolor single-pixel digital holography technique. The intensity and phase images of an object are simultaneously obtained from the time-sequence intensity data captured using a single-pixel photodetector. Moreover, phase-structured light and phase-shifting interferometry are implemented using only a spatial light modulator without any mechanical movements. The adopted configuration dramatically simplifies the optical setup by removing both imaging optics and the resultant chromatic aberration. The effectiveness of the proposed technique is demonstrated numerically and experimentally.