Wide-field spatiospectral interferometry: theory and imaging properties

Iacchetta, Alexander S.; Fienup, James R.

doi:10.1364/josaa.34.001896

Cited by 2 publications

(3 citation statements)

References 16 publications

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“…In reality, a more sophisticated algorithm is used to generate a spatial-spectral datacube covering the wide field of view. 11,12 By providing a long delay line scan, spectral information for the observed sources is obtained. To obtain a spectral resolution R requires an optical path delay (OPD) scan range of δ = Rλ.…”

Section: Optical Layoutmentioning

confidence: 99%

The wide-field spatio-spectral interferometer: system overview, data synthesis and analysis

Juanola-Parramon

Iacchetta

Leisawitz

et al. 2018

Optical and Infrared Interferometry and Imaging VI

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The Wide-field Imaging Interferometry Testbed (WIIT) is a double Fourier (DF) interferometer operating at optical wavelengths, and provides data that are highly representative of those from a space-based far-infrared interferometer like SPIRIT. We have used the testbed to observe both geometrically simple and astronomically representative test scenes. Here we present an overview of the astronomical importance of high angular resolution at the far infrared, followed by the description of the optical set-up of WIIT, including the source simulator CHIP (Calibrated Hyperspectral Image Projector). We describe our synthesis algorithms used in the reconstruction of the input test scenes via a simulation of the most recent measurements. The updated algorithms, which include instruments artifacts that allow the synthesis of DF experimental data, are presented and the most recent results analyzed.

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Section: Optical Layoutmentioning

confidence: 99%

The wide-field spatio-spectral interferometer: system overview, data synthesis and analysis

Juanola-Parramon

Iacchetta

Leisawitz

et al. 2018

Optical and Infrared Interferometry and Imaging VI

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“…5 and 6 we have investigated an alternative method that combines Fourier-transform spectroscopy (FTS) [59] with diffractive imaging methods, which in principle should be able to resolve even very broad harmonic spectra. It turns out that these methods bear a strong conceptual similarity to a group of techniques in astronomy, which is called double Fourier interferometry [60], in which the stellar signal of different baseline telescopes is interfered through FTS interferometry to build a spectrally resolved Fourier-plane signal of the object.…”

Section: Imaging Spectrometrymentioning

confidence: 99%

“…Here we will discuss the two reconstruction methods that were used to generate images from these signals from this signal: Diffractive shear interferometry (DSI) and an adjusted form of Fourier holography (FTS-FH). These methods bear a strong conceptual resemblance to a hyper-spectral imaging approach from astronomy called double Fourier-interferometry [60,102], in which Fourier-transform spectroscopy (FTS) is applied on the signal from different radio or infrared baseline telescopes, which results in a signal that is similar to the one we obtain in our experiments. Consider two illumination beams, which are propagating from two high-harmonic sources S 1 and S 2 , that scatter from a specimen towards a detector in the far field.…”

Section: Spectrally Resolved Imaging Through Fourier-transform Spectr...mentioning

confidence: 99%

Lensless imaging with high-harmonic sources

de Beurs

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Coherent diffractive imaging (CDI) is a family of computational imaging techniques that uses iterative reconstruction algorithms to decipher the information encoded in one or more interference patterns to reconstruct an image of an object located in another propagation plane. The lensless nature of these techniques makes them well-suited for imaging with coherent extreme ultraviolet (EUV) or x-ray illumination as refractive optics are limited at these wavelengths. In particular, this work investigates the use of CDI techniques in combination with high-harmonic generation. High-harmonic generation~(HHG) sources can generate EUV illumination beams with a high degree of spatial coherence in a compact tabletop setup. In this work we use Fourier-Transform spectroscopy~(FTS) to separate sets of nearly monochromatic diffraction patterns from a broadband HHG diffraction pattern. These monochromatic diffraction patterns can used to reconstruct spectrally resolved images through reconstruction methods that are similar to those applied in conventional CDI. In Chapter 4 we describe how we use a common path interferometer and a noncollinear chirped pulse amplifier system to generate phase locked 25 fs pulse pairs with a central wavelength of approximately 800 nm and a combined pulse energy of 10 mJ. These infrared driving laser pulses are focused at slightly separated locations in a noble gas jet to upconvert them into a pair of almost identical high-harmonic pulses. In FTS-based imaging experiments, we illuminate a sample with the HHG pulse pairs and record the far-field diffraction pattern as a function of pulse-to-pulse time delay. The spatial separation of our two harmonic beams results in spatial interference between two laterally sheared copies of the diffraction pattern. As a consequence of the geometry, the spectrally separated diffraction patterns obtained in these measurements are similar, but not identical to the standard CDI case. In this work, we demonstrated an algorithm, called diffractive shear interferometry (DSI), to reconstruct images from such diffraction patterns. Using this algorithm, the information present in these diffraction patterns is used to reconstruct complex images of the sample. The reverse problem is either constrained by combining an diffraction pattern with a finite object support prior in Chapter 5 or with other diffraction patterns with a different relative orientation between the shear and the object. One of the advantages of coherent diffractive imaging techniques is that it they reconstruct the full complex electric field at the sample. In reflection mode, such phase difference can be easily attributed to height differences of the reflecting surface. However, most research in diffractive imaging has focused on transmission mode imaging. At the EUV wavelengths generated by HHG sources normal incidence reflection coefficients are vanishingly small. However towards grazing incidence the reflection coefficients approach one. Such a geometry does come at a cost of added experimental and computational complexity. While far-field diffraction between colinear planes can be described by a straight forward Fourier transform of the electric field, for the propagation between non-collinear planes, an additional non-linear coordinate transformation is required. This coordinate transformation depends on the tilt angle of the fields and becomes very sensitive to the exact tilt-angle towards grazing incidence. While CDI itself requires accurate knowledge of the wave propagation, a technique known as ptychography offers more flexibility, as it is often possible to solve for more variables than just the object field. In Chapter 7 we use that property to demonstrate an auto-calibration algorithm that can iteratively calibrate the tilt-angle during a ptychographic reconstruction. Using this approach we were able to refine the tilt angle close to the correct value even when the initial estimates were off by more than 5 degrees, greatly improving flexibility in reflection-mode lensless imaging.

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Wide-field spatiospectral interferometry: theory and imaging properties

Cited by 2 publications

References 16 publications

The wide-field spatio-spectral interferometer: system overview, data synthesis and analysis

The wide-field spatio-spectral interferometer: system overview, data synthesis and analysis

Lensless imaging with high-harmonic sources

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