VSL Dutch Metrology Institute

Delft, Netherlands

VSL Dutch Metrology Institute

Delft, Netherlands
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El Gawhary O.,VSL Dutch Metrology Institute | El Gawhary O.,Technical University of Delft
New Journal of Physics | Year: 2017

The interaction of electromagnetic waves with matter is at the foundation of the way we perceive and explore the world around us. In fact, when a field interacts with an object, signatures on the object's geometry and physical properties are recorded in the resulting scattered field and are transported away from the object, where they can eventually be detected and processed. An optical field can transport information through its spectral content, its polarization state, and its spatial distribution. Generally speaking, the field's spatial structure is typically subjected to changes under free-space propagation and any information therein encoded gets reshuffled by the propagation process. We must ascribe to this fundamental reason the fact that spectroscopy was known to the ancient civilizations already, and founded as modern science in the middle of seventeenth century, while to date we do not have an established scientific of field of 'spatial spectroscopy' yet. In this work we tackle this issue and we show how any field, whose evolution is dictated by Helmholtz equation, contains a universal and invariant spatial structure. When expressed in the framework of this spatial fabric, the spatial information content carried by any field reveals its invariant nature. This opens the way to novel paradigms in optical digital communications, inverse scattering, materials inspection, nanometrology and quantum optics. © 2017 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Gawhary O.E.,VSL Dutch Metrology Institute | Gawhary O.E.,Technical University of Delft | Severini S.,Centro Interforze Studi per le Applicazioni Militari
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

In this work we present an extensive study of the scaling symmetry typical of a paraxial wave theory. In particular, by means of a Lagrangian approach we derive the conservation law and the corresponding generalized charge associated with the scale invariance symmetry. In general, such a conserved charge, q s say, can take any value that remains constant during propagation. However, it is explicitly proven that for the whole class of physically realizable shape-invariant fields, that is, fields whose intensity distribution maintains its shape on propagation, qs must necessarily vanish. Finally, an interesting relation between such charge qs and the effective radius of a beam, as introduced by Siegman some years ago, is derived. © 2013 American Physical Society.


Gawhary O.E.,VSL Dutch Metrology Institute | Gawhary O.E.,Technical University of Delft | Adam A.J.L.,Technical University of Delft | Urbach H.P.,Technical University of Delft
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

It is known that, at optical frequencies, a simple interface between a perfect dielectric and a real metal can sustain the propagation of surface plasmon polaritons only for P-polarized electromagnetic waves, being S-polarized surface plasmons are prohibited. In this work, we formally show that, strictly speaking, both polarization states are in fact prohibited and that only P-polarized pseudosurface waves are allowed, which is what is encountered in the applications. The existence of such pseudosurface modes allows one to reconcile theory and experimental evidence, but also sets limits for them to be considered as modes bound to the interface. © 2014 American Physical Society.


Jeanneret B.,Federal Office of Metrology METAS | Rufenacht A.,Federal Office of Metrology METAS | Overney F.,Federal Office of Metrology METAS | Brom H.V.D.,VSL Dutch Metrology Institute | Houtzager E.,VSL Dutch Metrology Institute
Metrologia | Year: 2011

Over the last 15 years, research in ac Josephson voltage metrology has focused on two fundamentally different systems: the programmable and the pulse-driven Josephson voltage standards (JVSs). This paper reports the first high precision comparison between the two types of JVS. The METAS programmable voltage standard was moved from Switzerland to the Netherlands to be compared with the Dutch pulse-driven system during four days in November 2010. After a careful investigation of the systematic sources of errors, the comparison was made at a frequency of 500 Hz and an rms amplitude of 104 mV. At that level, the voltage difference measured between the fundamental frequency components of the two standards was -0.18 0.26 νV V-1 (k = 2), showing an excellent agreement between the two systems. © 2011 BIPM & IOP Publishing Ltd.


Filipski P.S.,National Research Council Canada | Van Den Brom H.E.,VSL Dutch Metrology Institute | Houtzager E.,VSL Dutch Metrology Institute
Measurement: Journal of the International Measurement Confederation | Year: 2012

This paper presents results of an international comparison of two quantum AC voltage standards based on pulse-driven Josephson arrays. The two systems differ in several hardware and software characteristics as well as in the level of automation, features which can influence the accuracy of transferring the quantum-standard voltage value to a calibrated instrument. The comparison was performed at 100 mV, 20 mV and 12 mV, at frequencies between 2.5 kHz and 100 kHz. An electronically-aided thermal transfer standard was used as a travelling standard. At the most accurate voltage and frequency point, 100 mV at 2.5 kHz, both laboratories agreed to better than 1 part in 10 6. © 2012 Elsevier Ltd. All rights reserved.


Mares A.I.,VSL Dutch Metrology Institute | Bergmans R.H.,VSL Dutch Metrology Institute
Measurement Science and Technology | Year: 2012

The use of optical coordinate measuring machines (CMMs) in industrial metrology shows great potential due to a high measurement speed and non-contact working principle. However, at present measurements performed by different users present too large variations. The uncertainty contributions are difficult to quantify and standard uncertainty evaluation procedures are needed. In order to address this issue, we have investigated the uncertainty sources of commercial optical CMMs. We present a comparison on chessboard standards between three different vision systems. The influence of critical measurement parameters on image formation and analysis is discussed. © 2012 IOP Publishing Ltd.


El Gawhary O.,VSL Dutch Metrology Institute | El Gawhary O.,Technical University of Delft
Optics Letters | Year: 2015

Nijboer - Zernike's circle polynomials are broadly used for the evaluation of aberrations of optical systems or, more generally, wavefront analysis. This is because they are orthogonal over a unit circle and are directly related to the balanced classical aberrations for imaging systems with circular pupils. However, such expansion and successive extensions of the original theory suffer from a key limitation: it does not preserve its form under propagation. This means that even if a Nijboer - Zernike expansion for a field is known on a given reference plane, as soon as another plane is considered, a new, different set of polynomials for the same field appears. The origin of this problem is to be ascribed to the fact that Nijboer - Zernike polynomials are a useful mathematical tool which, however, are not bound to the physics of the electromagnetic problem they are employed in. In this work, we show that a more appropriate modal expansion does exist that is not only orthogonal on the unit disk but is also invariant on propagation. Besides impacting the field of aberrations analysis and retrieval, the modal expansion introduced here holds an enormous potential for digital classical and quantum optical communications, optical metrology, and adaptive optics too. The practical implementation, physical interpretation, and visualization of this new modal expansion are all very straightforward. © 2015 Optical Society of America.


Van Den Brom H.E.,VSL Dutch Metrology Institute | Houtzager E.,VSL Dutch Metrology Institute
CPEM Digest (Conference on Precision Electromagnetic Measurements) | Year: 2010

This paper describes possible strategies towards minimizing or compensating the influence of the voltage leads when using a pulse driven AC Josephson voltage standard as a calculable reference source in practice. © 2010 IEEE.


El Gawhary O.,Technical University of Delft | El Gawhary O.,VSL Dutch Metrology Institute | Wiegmann A.,Technical University of Delft | Wiegmann A.,Physikalisch - Technische Bundesanstalt | And 3 more authors.
Optics Express | Year: 2013

Through-focus phase retrieval methods aim to retrieve the phase of an optical field from its intensity distribution measured at different planes in the focal region. By using the concept of spatial correlation for propagating fields, for both the complex amplitude and the intensity of a field, we can infer which planes are suitable to retrieve the phase and which are not. Our analysis also reveals why all techniques based on measuring the intensity at two Fourier-conjugated planes usually lead to a good reconstruction of the phase. The findings presented in this work are important for aberration characterization of optical systems, adaptive optics and wavefront metrology. © 2013 Optical Society of America.


Koops R.,VSL Dutch Metrology Institute | Fokkema V.,VSL Dutch Metrology Institute
Measurement Science and Technology | Year: 2014

The atomic force microscope (AFM) tapping mode is a highly sensitive local probing technique that is very useful to study and measure surface properties down to the atomic scale. The tapping mode is mostly implemented using the resonance of the first bending mode of the cantilever and therefore provides sensitivity mainly along the direction of this oscillation. Driven by the semiconductor industry, there is an increasing need for accurate measurements of nanoscale structures for side wall characterization by AFM that requires additional sensitivity in the lateral direction. The conventional tapping mode has been augmented by various authors, for example by tilting the cantilever system (Cho et al 2011 Rev. Sci. Instrum. 82 023707) to access the sidewall or using a torsion mode (Dai et al 2011 Meas. Sci. Technol. 22 094009) of the cantilever to provide additional lateral sensitivity. These approaches however trade lateral sensitivity for vertical sensitivity or still lack sensitivity in the remaining lateral direction. We present an approach towards true 3D sensitivity for AFM cantilevers based on simultaneous excitation and optical detection of multiple cantilever resonance modes along three axes. Tuning the excitation of the cantilever to specific frequencies provides a mechanism to select only those cantilever modes that have the desired characteristics. Additionally, cantilever engineering has been used to design and create a substructure within the cantilever that has been optimized for specific resonance behavior around 4 MHz. In contrast to the conventional approach of using a piezo to actuate the cantilever modulation, we present results on photo-thermal excitation using an intensity modulated low-power laser source. By tightly focusing the excitation spot on the cantilever we were able to attain a deflection efficiency of 0.7 nm W-1 for the first bending mode. The presented approach results in an efficient all optical excitation and deflection detection scheme where both the position of the spot to excite the cantilever and the spot position of the read-out beam provide additional parameters to fully control and optimize the multi-mode structure required for 3D AFM measurements. © 2014 IOP Publishing Ltd.

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