Near-field diffraction of gratings with surface defects

Sanchez‐Brea, Luis Miguel; Torcal-Milla, Francisco José

doi:10.1364/ao.49.002190

Cited by 15 publications

(7 citation statements)

References 12 publications

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“…In addition, due to the averaging process performed in equation (6), the variogram function is much smoother than the original intensity distribution. Influence of grating defects on the visibility of the fringes has been reported by the authors in previous works [23,24]. An example is shown in figure 4 where the variogram function has been obtained for two sections of figure 3.…”

Section: Resultsmentioning

confidence: 56%

Dual self-image technique for beam collimation

Herrera-Fernandez

Sanchez‐Brea

Torcal-Milla

et al. 2016

J. Opt.

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Abstract. We propose an accurate technique for obtaining highly collimated beams, which also allows testing the collimation degree of a beam. It is based on comparing the period of two different self-images produced by a single diffraction grating. In this way, variations in the period of the diffraction grating do not affect to the measuring procedure. Self-images are acquired by two CMOS cameras and their periods are determined by fitting the variogram function of the self-images to a cosine function with polynomial envelopes. This way, loss of accuracy caused by imperfections of the measured self-images is avoided. As usual, collimation is obtained by displacing the collimation element with respect to the source along the optical axis. When the period of both self-images coincides, collimation is achieved. With this method neither a strict control of the period of the diffraction grating nor a transverse displacement, required in other techniques, are necessary. As an example, a LED considering paraxial approximation and point source illumination is collimated resulting a resolution in the divergence of the beam of δφ = ±1.57 µrad.

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Section: Resultsmentioning

confidence: 56%

Dual self-image technique for beam collimation

Herrera-Fernandez

Sanchez‐Brea

Torcal-Milla

et al. 2016

J. Opt.

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“…We also observed that a larger inter-grating distance and then a larger shear distance allows one to reduce the sensitivity of the device to the surface defects of the first grating [13]. However, the drawback of increasing shearing distance is observable by comparison of the four different curves: the higher spatial frequencies features disappear as one would expect, letting only the larger features of the mirror slope error for larger shear distance.…”

Section: Experiments and Discussionmentioning

confidence: 69%

Shearing interferometer spatial resolution for at-wavelength hard X-ray metrology

Berujon¹,

Wang²,

Ziegler³

et al. 2012

AIP Conference Proceedings

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Grating interferometers are very attractive tools to perform at-wavelength metrology as they are able to measure wavefront gradients with tens of nanoradians accuracy and with a low sensitivity to mechanical vibrations. However, when performing hard-X-ray at-wavelength metrology on reflective optics additional effort is needed to compensate for the reduction of spatial resolution caused by the grazing incidence angle of the probe. As the shear effect may limit the accessible detectable frequencies, special care must be taken on the choice of the working Talbot order in order to find the best compromise between sensitivity, robustness to noise and spatial resolution.

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“…The ability of the AP approach to deal with wideband signals allows it to cover a wider range of practically relevant situations. Among examples are nonlinear ultrasound imaging [4], [14], speech processing [20], [70], and complicated cases of optical interference/diffraction setups [73]. Moreover, it can also be of great use in time-critical imaging settings by providing high modulator estimation accuracy at low sampling rates of the signal (see, e.g., [72]).…”

Section: Extensions and Generalizations A Demodulation In Higher Dime...mentioning

confidence: 99%

Fast and Accurate Amplitude Demodulation of Wideband Signals

Gabrielaitis

2021

Preprint

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Amplitude demodulation is a classical operation used in signal processing. For a long time, its effective applications in practice have been limited to narrowband signals. In this work, we generalize amplitude demodulation to wideband signals. We pose demodulation as a recovery problem of an oversampled corrupted signal and introduce special iterative schemes belonging to the family of alternating projection algorithms to solve it. Sensibly chosen structural assumptions on the demodulation outputs allow us to reveal the high inferential accuracy of the method over a rich set of relevant signals. This new approach surpasses current state-of-the-art demodulation techniques apt to wideband signals in computational efficiency by up to many orders of magnitude with no sacrifice in quality. Such performance opens the door for applications of the amplitude demodulation procedure in new contexts. In particular, the new method makes online and largescale offline data processing feasible, including the calculation of modulator-carrier pairs in higher dimensions and poor sampling conditions, independent of the signal bandwidth. We illustrate the utility and specifics of applications of the new method in practice by using synthetic and natural speech signals.

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Near-field diffraction of gratings with surface defects

Cited by 15 publications

References 12 publications

Dual self-image technique for beam collimation

Dual self-image technique for beam collimation

Shearing interferometer spatial resolution for at-wavelength hard X-ray metrology

Fast and Accurate Amplitude Demodulation of Wideband Signals

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