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    46126 results match your criteria Applied optics[Journal]

    1 OF 923

    Multiwavelength off-axis digital holography with an angle of more than 40  degrees and no beam combiner to generate interference light.
    Appl Opt 2017 May;56(13):F200-F204
    We propose single-shot multiwavelength digital holography with an extremely large incident angle and show the digital recording of multiple object waves at multiple wavelengths with an angle of more than 40 degrees and no beam combiner to generate interference light. Both the avoidance of the crosstalk between the object waves at different wavelengths and the space-bandwidth extension are simultaneously achieved with a single-shot exposure of a monochromatic image sensor and a reference beam even when the wavelength difference between the object waves is small. An extremely large angle can be set by utilizing the signal theory. Read More

    Self-calibration for lensless color microscopy.
    Appl Opt 2017 May;56(13):F189-F199
    Lensless color microscopy (also called in-line digital color holography) is a recent quantitative 3D imaging method used in several areas including biomedical imaging and microfluidics. By targeting cost-effective and compact designs, the wavelength of the low-end sources used is known only imprecisely, in particular because of their dependence on temperature and power supply voltage. This imprecision is the source of biases during the reconstruction step. Read More

    Surface structural damage study in cortical bone due to medical drilling.
    Appl Opt 2017 May;56(13):F179-F188
    A bone's fracture could be produced by an excessive, repetitive, or sudden load. A regular medical practice to heal it is to fix it in two possible ways: external immobilization, using a ferule, or an internal fixation, using a prosthetic device commonly attached to the bone by means of surgical screws. The bone's volume loss due to this drilling modifies its structure either in the presence or absence of a fracture. Read More

    Real object pickup method of integral imaging using offset lens array.
    Appl Opt 2017 May;56(13):F167-F172
    We propose the pickup system of integral imaging using the offset lens array (OLA), which is a useful optical component for both the pickup and display processes. The main purpose of our system is resolving the pseudoscopic image problem of integral imaging. Also, the flipped image of integral imaging that has the wrong perspective information can be removed by adding an external barrier in the display process. Read More

    Observation of dehydration dynamics in biological tissues with terahertz digital holography [Invited].
    Appl Opt 2017 May;56(13):F173-F178
    A terahertz (THz) digital holographic imaging system is utilized to investigate natural dehydration processes in three types of biological tissues, including cattle, mutton, and pork. An image reconstruction algorithm is applied to remove the diffraction influence of THz waves and further improve clarity of THz images. From THz images of different biological specimens, distinctive water content as well as dehydration features of adipose and muscle tissues are precisely distinguished. Read More

    Quality assessment of refocus criteria for particle imaging in digital off-axis holography.
    Appl Opt 2017 May;56(13):F158-F166
    This paper proposes a quality assessment of focusing criteria for imaging in digital off-axis holography. In the literature, several refocus criteria have been proposed in the past to get the best refocus distance in digital holography. As a general rule, the best focusing plane is determined by the reconstruction distance for which the criterion function presents a maximum or a minimum. Read More

    Fast autofocusing in digital holography using the magnitude differential.
    Appl Opt 2017 May;56(13):F152-F157
    Typical methods of automatic estimation of focusing in digital holography calculate every single reconstructed frame to get a critical function and then ascertain the focal plane by finding the extreme value of that function. Here, we propose a digital holographic autofocusing method that computes the focused distance using the first longitudinal difference of the magnitude of the reconstructed image. We demonstrate the proposed method with both numerical simulations and optical experiments of amplitude-contrast and phase-contrast objects. Read More

    Improved zonal integration method for high accurate surface reconstruction in quantitative deflectometry.
    Appl Opt 2017 May;56(13):F144-F151
    In quantitative deflectometry, a test optical component is generally divided into numerous sample regions by the pixels on a camera's CCD detector, and the adjacent intervals of sample regions are unequal in off-axis configurations. In this case, errors will be introduced in the reconstruction result if the traditional Southwell zonal integration method is arbitrarily used. Thus, an improved zonal method is proposed in this paper. Read More

    Computer-generated hologram with occlusion effect using layer-based processing.
    Appl Opt 2017 May;56(13):F138-F143
    We propose a layer-based algorithm with single-viewpoint rendering geometry to calculate a three-dimensional (3D) computer-generated hologram (CGH) with occlusion effect. The 3D scene is sliced into multiple parallel layers according to the depth information. Slab-based orthographic projection is implemented to generate shading information for each layer, which renders hidden primitives for occlusion processing. Read More

    Iterative phase retrieval based on variable wavefront curvature.
    Appl Opt 2017 May;56(13):F134-F137
    An alternative phase retrieval technique is discussed in this paper, which offers some advantages for the obtained resolution and reconstruction procedure. In contrast to commonly applied iterative phase retrieval routines, diffraction patterns with varying distance between the illumination source and the object are recorded. This has the same effect as changing the object sensor distance, albeit offering the advantage of preserving the resolution. Read More

    Experimental demonstration of square Fresnel zone plate with chiral side lobes.
    Appl Opt 2017 May;56(13):F128-F133
    In this study, we introduce what we believe is a novel holographic optical element called a chiral square Fresnel zone plate (CSFZP). The chirality is imposed on a square Fresnel zone plate (SFZP) using a nonclassical technique by rotating the half-period zones relative to one another. The rotation of the half-period zones, in turn, twists the side lobes of the diffraction pattern without altering the focusing properties inherent to a SFZP. Read More

    Optical defocus noise suppressing by using a pinhole-polarizer in Fresnel incoherent correlation holography.
    Appl Opt 2017 May;56(13):F121-F127
    We propose the method that suppresses the defocus noise optically in the Fresnel incoherent correlation holographic system using a pinhole-polarizer (PP), which is made by punching a pinhole on the linear polarizer. The system configuration of this suggestion is based on the original system with optical-sectioning capability, which is realized by presenting the phase-pinhole on the phase-only spatial light modulator. In our system, the phase-pinhole is replaced with a PP. Read More

    Projection-type integral imaging system using a three-dimensional screen composed of a lens array and a retroreflector film.
    Appl Opt 2017 May;56(13):F105-F111
    We propose an improved projection-type integral imaging system using a three-dimensional (3D) screen consisting of a lens array and a retroreflector film in this paper. The projection-type integral imaging system suffers from the disadvantage of low-visibility images because of the inherently small exit pupil size of the projector. In order to resolve this problem, we adopt a 3D screen to avoid the demerits of a diffuser screen, such as off-screen image blur and loss of parallax. Read More

    Full-color holographic display with increased-viewing-angle [Invited].
    Appl Opt 2017 May;56(13):F112-F120
    Among the important features of holographic displays are the wide viewing angles and the full color of the reconstructed images. The present work focuses on achievement of both features. We propose an increased-viewing-angle full-color holographic display using two tiled phase-only spatial light modulators (SLMs), a 4f concave mirrors system, and a temporal-spatial multiplexing method. Read More

    Co-axis digital holography based on sinusoidal phase modulation using generalized lock-in detection.
    Appl Opt 2017 May;56(13):F97-F104
    Sinusoidal phase modulating (SPM) interferometers are used to precisely measure complex light fields with simple interferometric setups. Recently, a generalized lock-in technique has been proposed for optimizing the signal extraction in phase-modulated interferometers. This article shows its applicability in digital holography as well as digital holographic interferometry. Read More

    Self-interference compressive digital holography with improved axial resolution and signal-to-noise ratio.
    Appl Opt 2017 May;56(13):F91-F96
    Fresnel incoherent correlation holography (FINCH) was proposed to break the barrier of spatial incoherent digital holographic imaging and show the potential of super-resolution imaging preferences. We developed FINCH as a compressive sensing modality and reconstruction procedure as an inverse problem in order to realize 3D tomographic imaging. Improved axial resolution is obtained via compressive reconstruction. Read More

    Speeding up image quality improvement in random phase-free holograms using ringing artifact characteristics.
    Appl Opt 2017 May;56(13):F61-F66
    A holographic projector utilizes holography techniques. However, there are several barriers to realizing holographic projections. One is deterioration of hologram image quality caused by speckle noise and ringing artifacts. Read More

    Quasi-three-dimensional particle imaging with digital holography.
    Appl Opt 2017 May;56(13):F53-F60
    In this work, approximate three-dimensional structures of microparticles are generated with digital holography using an automated focus method. This is done by stacking a collection of silhouette-like images of a particle reconstructed from a single in-line hologram. The method enables estimation of the particle size in the longitudinal and transverse dimensions. Read More

    Large real-time holographic 3D displays: enabling components and results.
    Appl Opt 2017 May;56(13):F45-F52
    A holographic 3D display with 300  mm×200  mm active area was built. The display includes a spatial light modulator that modulates amplitude and phase of light and thus enables holographic reconstruction with high efficiency. Furthermore, holographic optical elements in photopolymer films and laser light sources are used. Read More

    Rendering of specular curved objects in polygon-based computer holography.
    Appl Opt 2017 May;56(13):F37-F44
    A realistic rendering technique is presented for creating large-scale computer-generated holograms. The technique is based on the polygon-based method, but allows specular curved surfaces to be reconstructed without increasing the number of polygons. In this technique, specular flat surfaces are transformed into curved surfaces. Read More

    Shift multiplexing with a spherical wave in holographic data storage based on a computer-generated hologram.
    Appl Opt 2017 May;56(13):F31-F36
    A holographic data storage system based on a computer-generated hologram (CGH) is simple and compact because a hologram of a data page is recorded through an imaging system without an additional optical path for a reference beam. In this paper, to improve the recording density of the holographic data storage based on a CGH, a shift multiplexing method using a spherical wave is proposed. A data page to be stored and a spherical wave are simultaneously reconstructed from a single CGH. Read More

    Autoencoder-based holographic image restoration.
    Appl Opt 2017 May;56(13):F27-F30
    We propose a holographic image restoration method using an autoencoder, which is an artificial neural network. Because holographic reconstructed images are often contaminated by direct light, conjugate light, and speckle noise, the discrimination of reconstructed images may be difficult. In this paper, we demonstrate the restoration of reconstructed images from holograms that record page data in holographic memory and quick response codes by using the proposed method. Read More

    Analysis of the noise in backprojection light field acquisition and its optimization.
    Appl Opt 2017 May;56(13):F20-F26
    Light field reconstruction from images captured by focal plane sweeping can achieve high lateral resolution comparable to the modern camera sensor. This is impossible for the conventional micro-lenslet-based light field capture systems. However, the severe defocus noise and the low depth resolution limit its applications. Read More

    Sparse light fields in coherent optical metrology [Invited].
    Appl Opt 2017 May;56(13):F14-F19
    In this publication, we demonstrate that recording the mutual intensity, instead of a wavefront, enables interferometric measurements with multiple independent light sources at the same time. This scheme can, for example, be used to overcome the problem of a limited acceptance angle of imaging systems in interferometry. We further show that, for a finite number of light sources, measuring a subspace of the mutual intensity equals the recording of the corresponding light field, which is sparse in phase space. Read More

    Investigation on vibration excitation of debonded sandwich structures using time-average digital holography.
    Appl Opt 2017 May;56(13):F7-F13
    Sandwich structures, in the modern aerospace industry, are more sought after due to their high strength to stiffness ratio resulting in significant weight gains. Optical techniques like time-average holography and shearography are preferred in industries for inspection of huge sandwich and composite panels because of whole-field (full coverage) inspection in a lesser time leading to large savings in cost. These techniques conventionally use sinusoidal frequency sweep to capture the local resonance of defective regions. Read More

    High brightness, low coherence, digital holographic microscopy for 3D visualization of an in-vitro sandwiched biological sample.
    Appl Opt 2017 May;56(13):F1-F6
    We achieve practically a bright-field digital holographic microscopy (DHM) configuration free from coherent noise for three-dimensional (3D) visualization of an in-vitro sandwiched sarcomere sample. Visualization of such sandwiched samples by conventional atomic force microscope (AFM) is impossible, while visualization using DHM with long coherent lengths is challenging. The proposed configuration is comprised of an ultrashort pulse laser source and a Mach-Zehnder interferometer in transmission. Read More

    Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America B.
    Appl Opt 2017 May;56(13):DH1-DH4
    The OSA Topical Meeting on Digital Holography and 3D Imaging (DH) was held 25-28 July 2016 in Heidelberg, Germany, as part of the Imaging Congress. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. This year, AO and the Journal of the Optical Society of America B (JOSA B) jointly decided to have one such feature issue in each journal. Read More

    Comparative study of fully three-dimensional reconstruction algorithms for lens-free microscopy.
    Appl Opt 2017 May;56(13):3939-3951
    We propose a three-dimensional (3D) imaging platform based on lens-free microscopy to perform multiangle acquisitions on 3D cell cultures embedded in extracellular matrices. Lens-free microscopy acquisitions present some inherent issues such as the lack of phase information on the sensor plane and a limited angular coverage. We developed and compared three different algorithms based on the Fourier diffraction theorem to obtain fully 3D reconstructions. Read More

    Very accurate temperature control of bones by a CO2 laser for medical applications.
    Appl Opt 2017 May;56(13):3923-3928
    In this paper, we show that the temperature of porcine bone samples can be maintained to a constant value within the range of 40°C-75°C. For this temperature range, it was also shown that a porcine bone sample could be kept at a given temperature within a fraction of a degree Celsius. This method relies on a real-time feedback computer control between a noncontact sensor and a CO2 laser operating at a typical repetition rate within the 5-20 kHz range. Read More

    Quantitative measurements of turbid liquids via structured laser illumination planar imaging where absorption spectrophotometry fails.
    Appl Opt 2017 May;56(13):3929-3938
    A comparison between the commonly used absorption spectrophotometry and a more recent approach known as structured laser illumination planar imaging (SLIPI) is presented for the characterization of scattering and absorbing liquids. Water solutions of milk and coffee are, respectively, investigated for 10 different levels of turbidity. For the milk solutions, scattering is the dominant process, while the coffee solutions have a high level of absorption. Read More

    Porosity and optical properties of zirconia films prepared by plasma ion assisted deposition.
    Appl Opt 2017 May;56(13):3913-3922
    The porosity of zirconia films prepared by plasma ion assisted deposition has been investigated by means of optical (spectrophotometric) and nonoptical analytic techniques such as transmission electron microscopy, x-ray reflection, and energy dispersive x-ray spectroscopy. A discrimination between large (open) and small (closed) pores was achieved by means of measurement of the thermal and vacuum-to-air shift. Depending on the level of plasma assistance during film preparation, the porosity was found to vary between 30 vol. Read More

    Improving chemical species tomography of turbulent flows using covariance estimation.
    Appl Opt 2017 May;56(13):3900-3912
    Chemical species tomography (CST) experiments can be divided into limited-data and full-rank cases. Both require solving ill-posed inverse problems, and thus the measurement data must be supplemented with prior information to carry out reconstructions. The Bayesian framework formalizes the role of additive information, expressed as the mean and covariance of a joint-normal prior probability density function. Read More

    Sinusoidal phase-modulating interferometer with ellipse fitting and a correction method.
    Appl Opt 2017 May;56(13):3895-3899
    In a sinusoidal phase-modulating interferometer, sinusoidal modulation of the phase of the laser or the reference wave is necessary. However, modulation of the phase also involves an intensity modulation of the light, which leads to a measurement error if conventional signal processing is used. In addition, the error of modulation depth and the phase delay of demodulation also increase the measurement error. Read More

    High resolution flash three-dimensional LIDAR systems based on polarization modulation.
    Appl Opt 2017 May;56(13):3889-3894
    Two high resolution flash LIDAR systems based on polarization modulation are demonstrated in this paper. One utilizes a polarization beam splitter (PBS) and two charge coupled device (CCD) arrays; the other utilizes a micro-polarizer array and a CCD array. Compared with the traditional flash LIDAR systems, the main advantage of the presented flash LIDAR systems is replacing high bandwidth detectors with a polarization modulator and low bandwidth detectors. Read More

    Alignment sensing for optical cavities using radio-frequency jitter modulation.
    Appl Opt 2017 May;56(13):3879-3888
    Alignment sensing is often required in precision interferometry applications such as Advanced LIGO in order to achieve the optimum performance. Currently favored sensing schemes rely on the use of two separate radio-frequency (RF) quadrant photodetectors and Gouy phase telescopes to determine the alignment of a beam relative to an optical cavity axis. In this paper, we demonstrate an alternative sensing scheme that has potential advantages over the current standard schemes. Read More

    How clean is the solvent you use to clean your optics? A vibrational sum-frequency-generation study.
    Appl Opt 2017 May;56(13):3875-3878
    Solvents for cleaning optics often come into contact with plastic and/or rubber during storage and transfer. To explore the effects that exposure to these materials can have on solvents, we used vibrational sum-frequency-generation spectroscopy to study a silica optic following cleaning with solvents that had come into contact with either low-density polyethylene, high-density polyethylene, or rubber. Our studies show that even brief contact of acetone, methanol, or isopropanol with plastic or rubber can cause otherwise pure solvents to leave a persistent residue. Read More

    Comparative assessment of erbium fiber ring lasers and reflective SOA linear lasers for fiber Bragg grating dynamic strain sensing.
    Appl Opt 2017 May;56(13):3867-3874
    Fiber Bragg grating (FBG) dynamic strain sensors using both an erbium-based fiber ring laser configuration and a reflective semiconductor optical amplifier (RSOA)-based linear laser configuration are investigated theoretically and experimentally. Fiber laser models are first presented to analyze the output characteristics of both fiber laser configurations when the FBG sensor is subjected to dynamic strains at high frequencies. Due to differences in the transition times of erbium and the semiconductor (InP/InGaAsP), erbium-doped fiber amplifier (EDFA)- and RSOA-based fiber lasers exhibit different responses and regimes of stability when the FBG is subjected to dynamic strains. Read More

    Thermal stress and end-bulging in monoclinic crystals: the case study of double tungstates.
    Appl Opt 2017 May;56(13):3857-3866
    An analytical description of the thermal stress and end-bulging component of thermal lensing is presented for monoclinic laser crystals, taking into account the anisotropy of their optical, thermal, and elastic properties for the first time, to the best of our knowledge. The geometry of longitudinal diode-pumping (plane stress approximation) is considered. The developed approach is applied to the monoclinic double tungstates (MDTs), Yb:KGW, Yb:KYW, and Yb:KLuW, yielding values of normal and shear stresses, tensile stress, and the end-bulging term. Read More

    Extracting and compensating for FOG vibration error based on improved empirical mode decomposition with masking signal.
    Appl Opt 2017 May;56(13):3848-3856
    Vibration is an important error source in fiber-optic gyroscopes (FOGs), and the extraction and compensation of vibration signals are important ways to eliminate the error and improve the accuracy of FOG. To decompose the vibration signal better, a new algorithm based on empirical mode decomposition (EMD) with masking signal is proposed in this paper. The masking signal is a kind of sinusoidal signal, and the frequency and amplitude of the masking signal are selected using improved particle swarm optimization. Read More

    Tunable passively Q-switched thulium-fluoride fiber laser in the S+/S band (1450.0 to 1512.0  nm) region using a single-walled carbon-nanotube-based saturable absorber.
    Appl Opt 2017 May;56(13):3841-3847
    A tunable passively Q-switched for S+/S band thulium-fluoride fiber (TFF) laser using single-walled carbon nanotubes as a saturable absorber is proposed and demonstrated. The tunability of the proposed laser covers a wavelength region of 1450.0-1512. Read More

    Digital micromirror device camera with per-pixel coded exposure for high dynamic range imaging.
    Appl Opt 2017 May;56(13):3831-3840
    In this paper, we overcome the limited dynamic range of the conventional digital camera, and propose a method of realizing high dynamic range imaging (HDRI) from a novel programmable imaging system called a digital micromirror device (DMD) camera. The unique feature of the proposed new method is that the spatial and temporal information of incident light in our DMD camera can be flexibly modulated, and it enables the camera pixels always to have reasonable exposure intensity by DMD pixel-level modulation. More importantly, it allows different light intensity control algorithms used in our programmable imaging system to achieve HDRI. Read More

    Experimental study of coherent accumulation based on sequence shifting and a genetic algorithm.
    Appl Opt 2017 May;56(13):3824-3830
    Because there is a certain phase difference between the two adjacent samples of an analog-to-digital converter for a heterodyne signal, we propose to eliminate the random phases in the coherent accumulation by shifting the sampling sequences with different steps. A genetic algorithm is used to determine the shifting steps of the sequences. An experiment has been conducted to verify the effectiveness of our approach. Read More

    Theoretical design for generation of slow light in a two-dimensional magneto optical trap using electromagnetically induced transparency.
    Appl Opt 2017 May;56(13):3817-3823
    In this paper, we propose a novel technique for slow light experiments using electromagnetically induced transparency using a two-dimensional magneto optical trap (2D-MOT). A compact 2D-MOT design efficient for quantum memory applications with adjustable optical depth (OD) is proposed. We estimated the OD for our 2D-MOT setup and found that light group velocities as low as 1. Read More

    100-nm tunable femtosecond Cr:LiSAF laser mode locked with a broadband saturable Bragg reflector.
    Appl Opt 2017 May;56(13):3812-3816
    We report broad tunability of a femtosecond (fs) diode-pumped Cr:LiSAF laser mode-locked with a broadband saturable Bragg reflector (SBR). The SBR had seven pairs of AlxOy(n∼1.5) and Al0. Read More

    Two-photon microscopy with enhanced contrast and resolution.
    Appl Opt 2017 May;56(13):3799-3805
    A method combining the saturation effect with the ratio concerned quadratic intensity weighted subtraction (RQIWS) algorithm for resolution and contrast enhancement in a two-photon microscopy system is presented in this paper. In the proposed method, the saturation effect is utilized to get a profile-extended solid spot and a center-shrunken doughnut-shaped spot for a smaller effective point spread function, which enhances the resolution of the system. The RQIWS algorithm uses the intensity ratio of the two original images acquired respectively with the solid spot and the doughnut-shaped spot as one of the subtraction parameters and takes the fluorescence quadratic dependence of excitation intensity into account for better subtraction results compared with the intensity weighted subtraction algorithm in a two-photon excitation system. Read More

    Tracking background-oriented schlieren for observing shock oscillations of transonic flying objects.
    Appl Opt 2017 May;56(13):3789-3798
    A detailed understanding of the in-flight behavior of high-speed flying objects is useful in the forensic investigation of crime scenes. In particular, for transonic flying objects with associated unsteady shock waves, long-duration and high-resolution measurements are desirable but difficult with conventional optical visualization methods. In this study, we propose a tracking background-oriented schlieren (BOS) method that uses a mirror-based high-speed optical axis controller and a striped retroreflective background. Read More

    Narrow-linewidth broadly tunable Yb-doped Q-switched fiber laser using multimode interference filter.
    Appl Opt 2017 May;56(13):3783-3788
    A narrow-linewidth broadly tunable Yb-doped Q-switched fiber laser using an acousto-optic modulator and multimode interference filter (MMIF) in the linear bulk cavity resonator and an all-fiber ring cavity resonator has been demonstrated. Insertion of an MMIF in the linear cavity resonator using bulk components decreased the spectral bandwidth of the Q-switched signal by two orders of magnitude from 11 to less than 0.1 nm. Read More

    Standoff monitoring of aqueous aerosols using nanosecond laser-induced breakdown spectroscopy: droplet size and matrix effects.
    Appl Opt 2017 May;56(13):3773-3782
    Nanosecond laser-induced breakdown spectroscopy has been examined for the analysis of suspended matter in a free stream of air. The real-time monitoring of this scenario poses major challenges for an accurate categorization due to its changing characteristics such as composition, size, and density of particles. The effects of particle size and matrix in the optical emission responses registered from such scenarios have been evaluated. Read More

    Semiquantitative analysis of mercury in landfill leachates using double-pulse laser-induced breakdown spectroscopy.
    Appl Opt 2017 May;56(13):3730-3735
    Laser-induced breakdown spectroscopy (LIBS) is showing to be a promising, quick, accurate, and practical technique to detect and measure metal contaminants and nutrients in urban wastes and landfill leachates. Although conventional LIBS presents some limitations, such as low sensitivity, when used in the single pulse configuration if compared to other spectroscopic techniques, the use of the double-pulse (DP) configuration represents an adequate alternative. In this work DP LIBS has been applied to the qualitative and quantitative analysis of mercury (Hg) in landfill leachates. Read More

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