Digital holography

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Development of digital holography in the long wave infrared range for assessment of space reflectors

Development of digital holography in the long wave infrared range for assessment of space reflectors

lasers with thermal infrared imagers. This paper presents preliminary results obtained by both the consortium formed by CSL and the MRC, especialized in digital holography reconstruction. An innovative configuration seems appropriate for measuring deformation of space reflectors without considering specific optics such as null lenses (in the case of parabola) or complicated and expensive illumination optics (in the case of ellipse). It consists of illuminating the reflector by a speckle wave, producing an artificial speckle wavefront at the level of the observed surface. The object wavefront can then be recorded either by electronic speckle pattern interferometry or digital holography. Laboratory investigations on small specular objects are also presented. They undergo rotations which have been measured by the proposed technique and compared to another measurement method. Afterwards early results obtained with a demonstration reflector from a previous ESA project are presented.
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MOTION COMPENSATION IN DIGITAL HOLOGRAPHY FOR RETINAL IMAGING

MOTION COMPENSATION IN DIGITAL HOLOGRAPHY FOR RETINAL IMAGING

Digital holography faces several issues altering images quality. Eye motion during image acquisition distorts the signal. In order to stabilize images of retinal features, im- age registration can be used. It consists in finding the geo- metric transformation to align two images. Medical image registration techniques have been developped during the past years [8]. Although most of the literature in this field concerns radiological modalities, several researches have been led in retinal imaging. The most widely used technique is feature- based registration of eye fundus images [9, 10]. However in our case, feature-based registration is not suitable because ob- jects of interest can disappear or even be replaced by another structure if the movement of the eye is too large, which could bias the search of feature points. This article is focused on cross-correlation stabilization to compensate lateral and axial motion of the whole image structure in laser Doppler holog- raphy and swept-source holographic OCT, respectively.
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(DH) Noise and Signal scaling factors in Digital Holography in week illumination: relationship with Shot Noise.

(DH) Noise and Signal scaling factors in Digital Holography in week illumination: relationship with Shot Noise.

ocis 090.0090,0.090.0995, 120.2880 I. INTRODUCTION Demonstrated by Gabor [1] in the early 50’s, the pur- pose of holography is to record, on a 2D detector, the phase and the amplitude of the light shining from an object under coherent illumination. Since a thin film does not provide a direct access to the recorded data, the holographic film has been replaced by 2D electronic detector in digital holography [2], whose main advantage is to perform the data acquisition and the holographic reconstruction numerically [3, 4]. Off-axis holography [5] is the oldest and the simplest configuration adapted to digital holography [4, 6, 7]. In off-axis digital holography, as well as in photographic plate holography, the reference or local oscillator (LO) beam is angularly tilted with re- spect to the object observation axis. It is then possible to record, with a single hologram, the two quadratures of the object’s complex field. However, the object field of view is reduced, since one must avoid the overlapping of the image with the conjugate image alias. Phase-shifting digital holography, which has been later introduced [8], records several images with a different phase for the LO beam. It is then possible to obtain the two quadratures of the field in an in-line configuration even though the con- jugate image alias and the true image overlap, because aliases can be removed by taking image differences.
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Digital Holography at Long-Wave Infrared for Measuring the Deformation of Large Space Reflectors under Thermal Vacuum

Digital Holography at Long-Wave Infrared for Measuring the Deformation of Large Space Reflectors under Thermal Vacuum

This method was successfully applied by Hansen in visible light for an object of the order of a few centimetres wide [6] by electronic speckle pattern interferometry (ESPI). Here we wish to validate the same principle but applied in LWIR digital holography and for a much larger target. For that purpose we have selected a spare space reflector, representative of ESA reflectors of interest. The latter is shown in Fig. 3 and consist of a parabolic mirror of 1.1 meter diameter and with a focal length of 1.58 meter.

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Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A

Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A

All submitted papers, including invited papers, have undergone peer review. We hope these articles will present state-of-the-art technological developments that are currently underway and stimulate further novel applications of digital holography and 3D imaging. The topical editors would like to thank all the contributors and the reviewers, without whom this feature issue would not have been possible. Finally, we wish the very best of success in the upcoming Digital Holography and 3D Imaging Conference, which will be held 22–26 June 2019 in Vancouver, Canada, as part of the OSA Imaging and Applied Optics Congress.
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Thermal infrared and terahertz digital holography and their applications

Thermal infrared and terahertz digital holography and their applications

Locatelli, M., et al., Real-time terahertz digital holography with a quantum cascade laser., Scientific Reports, 2015.. DIGITAL HOLOGRAPHY IN THZ WAVES. Locatelli, M., et al., Real-time [r]

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Signal and Noise scaling factors in digital holography

Signal and Noise scaling factors in digital holography

proportional to the squared acquisition duration, whereas the noise, which is equal to the shot noise [8], is proportional to the acquisition duration, and to the number of optical modes used for reconstruction (area of the spatial filter in pixel). These results validate our previous studies in digital holography with weak illumination [1-6]. 6. References

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Compressed digital holography: from micro towards macro

Compressed digital holography: from micro towards macro

b LTCI, CNRS, Télécom ParisTech, Université Paris-Saclay, Paris, France c iMinds, Technologiepark 19, Zwijnaarde, Belgium ABSTRACT The age of computational imaging is merging the physical hardware-driven approach of photonics with advanced signal processing methods from software-driven computer engineering and applied mathematics. The compressed sensing theory in particular established a practical framework for reconstructing the scene content using few linear combinations of complex measurements and a sparse prior for regularizing the solution. Compressed sensing found direct applications in digital holography for microscopy. Indeed, the wave propagation phenomenon in free space mixes in a natural way the spatial distribution of point sources from the 3-dimensional scene. As the 3-dimensional scene is mapped to a 2-dimensional hologram, the hologram samples form a compressed representation of the scene as well. This overview paper discusses contributions in the field of compressed digital holography at the micro scale. Then, an outreach on future extensions towards the real-size macro scale is discussed. Thanks to advances in sensor technologies, increasing computing power and the recent improvements in sparse digital signal processing, holographic modalities are on the verge of practical high-quality visualization at a macroscopic scale where much higher resolution holograms must be acquired and processed on the computer.
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Thermo-elastic deformation measurement of the EUCLID near infrared focal plane array by long wave infrared digital holography

Thermo-elastic deformation measurement of the EUCLID near infrared focal plane array by long wave infrared digital holography

Fig. 1. Optical set-up for the DH measurements of the displacements of the NI-DS. Fig. 2. Measurement of the displacements of the STMD by digital holography and in parallel with a visible interferometer. To determine the precision and accuracy of the DH instrument, parallel measurement of both piston and tilt of the STMD were performed with a commercial visible light interferometer (Fig. 2). This interferometer can achieve 0.01 µm accuracy for translation and 0.1 arcsec for rotation. This rotation amplitude represents a differential displacement between the opposite edges of the STMD of less than 0.02 µm. The interferometer can therefore be considered as the reference system compared to the expected performances of the DH instrument.
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Thermo-elastic deformation measurement of the Euclid near infrared focal plane array by long wave infrared digital holography

Thermo-elastic deformation measurement of the Euclid near infrared focal plane array by long wave infrared digital holography

A. Optical set-up The Digital Holography (DH) system was first assembled on an optical table in the laboratory to check the design. The optical set-up for the NI-DS test is shown at Fig. 1. It is composed of a beam-splitter (BS) that divides the CO 2 laser beam into a reference beam and an object beam. The reference beam is reflected on a piezo-reflector (PZT), which realizes the phase-stepping, and passes through a doublet of lenses (L1 and L2) that enlarge the reference beam to cover completely the camera detector. The camera is a VarioCam HD from Infratec equipped with a 1024 × 768 pixels microbolometer detector array, without any objective mounted.
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Digital Holography at Shot Noise Level

Digital Holography at Shot Noise Level

V. C ONCLUSION In this paper we have studied the noise limits in digital holography. We have shown that in high heterodyne gain of the holographic detection (achieved when the object field power is much weaker than the LO field power), the noise of the CCD camera can be neglected. Moreover by a proper arrangement of the holographic setup, that combines off-axis geometry with phase shifting acquisition of holograms, it is possible to reach the theoretical shot noise limit. We have studied theoretically this limit, and we have shown that it corresponds to 1 photo electron per pixel for the whole sequence of frame that is used to reconstruct the holographic image. This paradoxical result is related to the heterodyne detection, where the detec- tion bandwidth is inversely proportional to the measurement time. We have verified all our results experimentally, and we have shown that is possible to image an object at very low illumination levels. We have also shown that is possible to mimic the very weak illumination levels holograms obtained in experiments by Monte Carlo noise modeling. This opens the way to simulation of ”gedanken” holographic experiments in weak signal conditions.
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Digital Holography at Ultimate Shot Noise Level

Digital Holography at Ultimate Shot Noise Level

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignemen[r]

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In vivo laser Doppler holography of the human retina

In vivo laser Doppler holography of the human retina

* gl.puyo@gmail.com Abstract: The eye offers a unique opportunity for the non-invasive exploration of cardiovascular diseases. Optical angiography in the retina requires sensitive measurements, which hinders conventional full-field laser Doppler imaging schemes. To overcome this limitation, we used digital holography to perform laser Doppler perfusion imaging of human retina with near-infrared light. Two imaging channels with a slow and a fast CMOS camera were used simultaneously for real-time narrowband measurements, and offline wideband measurements, respectively. The beat frequency spectrum of optical interferograms recorded with the fast (up to 75 kHz ) CMOS camera was analyzed by short-time Fourier transformation. Power Doppler images drawn from the Doppler power spectrum density qualitatively revealed blood flow in retinal vessels over 512 × 512 pixels covering 2.4 × 2.4 mm 2 on the retina with a temporal resolution down to 1.6 ms. The sensitivity to lateral motion as well as the requirements in terms of sampling frequency are discussed.
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Digital in-line holography for near field observation of liquid-liquid flows under astigmatic conditions

Digital in-line holography for near field observation of liquid-liquid flows under astigmatic conditions

[1] Lamadie, F., L. Bruel and M. Himbert (2012). "Digital holographic measurement of liquid–liquid two-phase flows." Optics and Lasers in Engineering 50(12): 1716-1725. [2] Pan, G., and Meng, H., 2003. “Digital holography of particle fields: reconstruction by use of complex amplitude”. Appl. Opt., 42, pp. 827– 833.

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Digital in-line holography for the characterization of two phase flows in astigmatic systems

Digital in-line holography for the characterization of two phase flows in astigmatic systems

OCIS codes: (090.1995) Digital holography, (050.1940) Diffraction, (120.3940) Metrology 1. Introduction Digital Holography (DH) is well-known for allowing, in a single shot, the complete 3D reconstruction of any particulate flow. As highlighted by Lamadie et al. [1], DH involves a very simple measurement setup, that is not sensitive to vibrations and to most typical environmental factors, and is therefore particularly suitable for the characterization of two phase flows. The authors demonstrated the feasibility of the measurements for a liquid/liquid flow, considering a cuboid flow cell. However, most standard devices designed for chemical engineering (for instance pulsed columns, centrifugal extractor, etc.) exhibit a cylindrical geometry inducing astigmatism, thus rendering the classical hologram simulation and focusing methods, inappropriate.
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Combined holography and thermography in a single sensor through image-plane holography at thermal infrared wavelengths

Combined holography and thermography in a single sensor through image-plane holography at thermal infrared wavelengths

The present paper is a continuation of previous ones and we demonstrate for the first time to the best of our knowledge that LWIR digital holography allows simultaneous recording of the surface shape and temperature. Indeed the thermal background is incoherent by nature, thus only the information coming from the laser illumination and related to the object surface shape can be numerically reconstructed by DH. For that reason we need to consider image- plane DH or classical ESPI configurations for which the focus of the object (including its thermal background) is insured by the objective lens put in front of the thermographic camera.
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Phase-sensitive narrowband heterodyne holography

Phase-sensitive narrowband heterodyne holography

Yoshio Hayasaki, and Toyohiko Yatagai. Color digital holography using a single monochromatic imaging sensor. Opt. Lett., 37(15):3153–3155, Aug 2012. [33] Tatsuki Tahara, Akifumi Maeda, Yasuhiro Awatsuji, Takashi Kakue, Peng Xia, Kenzo Nishio, Shogo Ura, Toshihiro Kubota, and Osamu Matoba. Single-shot dual- illumination phase unwrapping using a single wavelength. Opt. Lett., 37(19):4002–4004, Oct 2012.

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Digital in-line holography for near field observation of liquid-liquid flow

Digital in-line holography for near field observation of liquid-liquid flow

1 Introduction Digital holography (DH) is a suitable technic, by which particles can be positioned in 3D space using a single camera. It is used for a broad range of applications including particle image velocimetry (PIV) and particle tracking velocimetry (PTV) [1], live cell imaging [2], and microscopy [3]. The first applications this technique to the characterization of dispersed phases in a two-phase flow were recently described [4], demonstrating that it is capable of simultaneously measuring the size and 3D position of droplets in rapid motion in the continuous phase [5]. Regardless of their applications, most of the examples reported in the literature refer to diffracting objects typically ranging in size from a few micrometers to a few hundred micrometers, observed at distances of the order of ten millimeters. This corresponds to a Fresnel number ( ⁄ , where is the particle diameter, the laser wavelength, and the distance between the
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Signal to noise characterization of an inverse problem-based algorithm for digital inline holography

Signal to noise characterization of an inverse problem-based algorithm for digital inline holography

{x ,y ,z } k k k Figure 1: The in-line holography setup We consider an in-line holographic setup (see figure 1) where studied particles are illuminated by the laser beam and both reference wave and object wave interfere and are recorded by the detector (typically a CCD sensor). The resulting hologram expression is a sum of terms depending on the location and size of each particle. In the case of digital holography of spherical micro-particles, each particle is described by few parameters {x k , y k , z k , r k }: x, y, z represent the spatial coordinates and r

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Real time Quantum state holography using coherent transients

Real time Quantum state holography using coherent transients

(Dated: 30 janvier 2006) In a two level atom, real-time quantum state holography is performed through interferences between quantum states created by a reference pulse and a chirped pulse resulting in coherent transients. A sequence of several measurements allows one to measure the real and imaginary parts of the excited state wave function. These measurements are performed during the interaction with the ultrashort laser pulse. The extreme sensitivity of this method to the pulse shape provides a tool for electric field measurement.

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