1,039 research outputs found
Coating layer on samples with roughness: numerical study for coherent Fourier scatterometry
No full textFor the development of integrated circuits, the accompanying metrology inside the fabrication process is essential. Non-imaging metrology of nanostructure has to be quick and non-destructive. The multilayers are crucial components of today's microprocessor nanostructures and reflective coatings. Coherent Fourier scatterometry (CFS), which is currently employed as a method for determining certain parameters of nanostructures and isolated particle detection, has not been investigated in the context of multilayer characterization. Retrieving the thickness of many wavelength-thick films using a coherent visible-range source at a full-complex-field measurement is the specific application where CFS might be advantageous. Furthermore, due to polishing in the realistic multilayers, the anticipated optical performance suffers from stochastic changes relating to surface roughness. Few non-imaging metrology methods take into consideration these statistic variances and thus are of interest for this study. Operating in the visible regime, CFS can become a viable candidate to provide cover layer reconstruction in the presence of surface roughness that has a correlation length bigger than the characteristic spot size i.e., in the range of microns. We present forward model results of multilayer structure as measured with visible range CFS modality. The influence of surface roughness is taken into account and the simulation results are discussed. Simulations of micron-sized layers of dielectric on silicon substrate suggest an influence on the far field intensity that motivates a future extended study on experimental multiple wavelength thick cover layer reconstruction in the presence of roughness. ImPhys/Pereira grou
A matter of perspective:How nanoscale optical defects limit cosmic-scale gravitational wave observations
No full textGround-based gravitational-wave (GW) detectors, such as LIGO, Virgo, and KAGRA, have revolutionised astronomy. Now, future detectors like the Einstein Telescope and Cosmic Explorer aim to achieve even greater sensitivity. Advanced optical simulations are crucial to overcoming the challenges faced by these complex interferometers. Finesse, the leading interferometer simulation tool in the GW community, supports the design and commissioning of these detectors by modeling optical, quantum, and mechanical effects. A key focus is understanding optical defects that distort the shape of the laser light and limit detector performance. This work explores how nanoscale defects affect GW observations and presents recent advancements in modeling their effects to guide the development of next-generation detector optics.</p
Superaccurate camera calibration via inverse rendering
No full textThe most prevalent routine for camera calibration is based on the detection of well-defined feature points on a purpose-made calibration artifact. These could be checkerboard saddle points, circles, rings or triangles, often printed on a planar structure. The feature points are first detected and then used in a nonlinear optimization to estimate the internal camera parameters. We propose a new method for camera calibration using the principle of inverse rendering. Instead of relying solely on detected feature points, we use an estimate of the internal parameters and the pose of the calibration object to implicitly render a non-photorealistic equivalent of the optical features. This enables us to compute pixel-wise differences in the image domain without interpolation artifacts. We can then improve our estimate of the internal parameters by minimizing pixel-wise least-squares differences. In this way, our model optimizes a meaningful metric in the image space assuming normally distributed noise characteristic for camera sensors. We demonstrate using synthetic and real camera images that our method improves the accuracy of estimated camera parameters as compared with current state-of-the-art calibration routines. Our method also estimates these parameters more robustly in the presence of noise and in situations where the number of calibration images is limited.<br/
Violence et culture politique en Allemagne entre les deux guerres
No full textViolence and political culture in interwar Germany, Bernd Weisbrod.
The entire German political culture has since 1918 integrated the acceptation of violence. The author follows the fatal consequences of this failing in the Weimar period, through the action of the Freikorps (Corps francs), then under the Third Reich. The banalization of evil in Germany (H. Arendt) was also a characteristic of the political culture.Weisbrod Bernd. Violence et culture politique en Allemagne entre les deux guerres. In: Vingtième Siècle, revue d'histoire, n°34, avril-juin 1992. Histoires d'Allemagnes. pp. 113-125
Study of the optical crosstalk in a heterodyne displacement gauge with cancelable circuit
No full textLong review of Bernd Heinrich\u27s A Year in the Maine Woods which praises the su
No full textLong review of Bernd Heinrich\u27s A Year in the Maine Woods which praises the subject matter and style of the naturalist\u27s investigations of Adams Hill near Weld. With a brief biography of the author
Talbot effect with aberrated beams
No full text© The International Society for Optical Engineering (SPIE).
Conference on Modeling Aspects in Optical Metrology (2ª. 2009. Múnich, Alemania).Diffraction gratings are one of the most used elements in optics and even in other fields of science. They are used also like part of measurement devices in scientific and industrial applications. As it is well known, self-imaging effect appears when a diffraction grating is illuminated with a coherent beam, such as a plane wave. This effect has been analyzed in depth and its behavior is well known under ideal grating and illumination conditions. Usually, the illumination beam is not perfectly collimated but presents a certain degree of aberration. The motivation of this work is to try to explain the behavior of the self-images of an ideal amplitude grating when it is illuminated by a non-perfect beam, that is, an aberrated beam. The known of this effect can help to understand how much the aberration of the light beam affects to the diffraction pattern, and more in depth, to the self-imaging phenomenon. The results presented in this work can be very useful in metrology applications, since sometimes the contrast obtained experimentally does not correspond to the theoretical predictions, usually due to aberrations in the light beam. For this, we have used a formalism based in the Rayleigh-Sommerfeld approach. We have modeled the aberrations by using the Zernike polynomials. On the other hand, we have considered all kinds of aberrations, spherical, coma, tilt, astigmatism, etc. As it is expected the contrast of the self-images decrease when the order of them increases and also when the aberration degree increase. In some cases, contrast inversion is also produced for high aberrations.Depto. de ÓpticaFac. de Ciencias FísicasTRUEpu
Effect of wavefront aberrations on a focused plenoptic imaging system: a wave optics simulation approach
No full textA plenoptic imaging system records simultaneously the intensity and the direction of the rays of light. This additional information allows many post processing features such as 3D imaging, synthetic refocusing and potentially evaluation of wavefront aberrations. In this paper the effects of low order aberrations on a simple plenoptic imaging system have been investigated using a wave optics simulations approach
Metrological characterization of a large aperture Fizeau for x-ray mirrors measurement
No full textThe European XFEL is a large facility under construction in Hamburg, Germany. It will provide a transversally fully coherent x-ray radiation with outstanding characteristics: high repetition rate (up to 2700 pulses with a 0.6 milliseconds long pulse train at 10Hz), short wavelength (down to 0.05 nm), short pulse (in the femtoseconds scale) and high average brilliance (1.61025 photons / s / mm2 / mrad2/ 0.1% bandwidth). Due to the very short wavelength and very high pulse energy, all the mirrors need to have high quality surface, to be very long, and at the same time to implement an effective cooling system. Matching these tight specifications and assessing them with high precision optical measurements is very challenging. In order to measure the mirrors and to characterize their interaction with the mechanical mounts, we equipped a Metrology Laboratory with a Large Aperture Fizeau. The system is a classical 100 mm diameter commercial Fizeau, with an additional expander providing a 300 mm diameter. Despite the commercial nature of the system, special care has been done in the polishing of the reference flats and in the expander quality. In this report, we show the preparation of the instrument, the calibration and the performance characterization, together with some preliminary results. We also describe the approach that we want to follow for the x-rays mirrors measurements. The final goal will be to characterize very long mirrors, almost 1 meter long, with nanometer accurac
Design of soft x-ray gratings for free electron lasers: from specification to characterization
No full textThe European XFEL is a large facility under construction in Hamburg, Germany. It will provide a transversally fully coherent X-ray radiation with outstanding characteristics: high repetition rate (up to 2700 pulses with a 0.6 milliseconds long pulse train at 10Hz), short wavelength (down to 0.05 nm), short pulse (in the femtoseconds scale) and high average brilliance (1.6•1025 photons / s / mm2 / mrad2/ 0.1% bandwidth). Due to the very short wavelength and very high pulse energy, mirrors have to present high quality surface, to be very long, and at the same time to implement an effective cooling system. Matching these tight specifications and assessing them with high precision optical measurements is very challenging. One of the three foreseen beamlines operates in the soft X-ray range and it is equipped with a diffractive monochromator. The monochromator is using a variable line spacing grating that covers the wavelength range from 4.6nm to 0.41 nm (energies from 270eV to 3000eV). The grating profile is blazed, and due to the small angle and relatively few lines/mm, it is also very challenging to realize and to be characterized. In this contribution we discuss about the requirements of the optics involved in the soft X-ray monochromator. We describe mirror and grating specifications, and the tests that could be carried out during and after the manufacturing in order to ensure the specifications match
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