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A linearly polarized optical field can be obtained by filtering a stochastic field through an ideal linear polarizer. The produced field possesses a given degree of paraxiality that, as proved in the present Letter, can be affected by the correlations of the original stochastic field. An example with Gaussian beams is discussed in detail.

The nonparaxial corrections for Bessel–Gauss beams were derived recently using two different approaches [Borghi et al., J. Opt. Soc. Am. A 18, 1618 (2001) and Vaveliuk et al., J. Opt. Soc. Am. A 24, 3297 (2007)]. However, the two obtained results do not agree, so it is necessary to determine which method is correct. In the most recent of those papers, Vaveliuk et al. claimed that their method is correct while the method described by Borghi et al. is incorrect. In the present work, just by solving the rigorous propagation problem, we show that exactly the converse is true.

Scatterometry is a well established technique currently utilized in research, as well as in industrial applications, to retrieve the properties of a given scatterer (the target) by looking at how the light coming from a certain source is diffracted in the far field. Currently the light source is often a discharge lamp that, after wavelength filtering, can be thought as a quasi-monochromatic, but spatially incoherent, source. In the present work, benefits of using a focused spot from a spatially coherent light source, as that emitted by a laser, are investigated on a theoretical viewpoint. The focused spot is scanned over the object of interest and, for each scan position, a far-field diffraction pattern is recorded. Our results show that spatially coherent light can sensibly increase the accuracy of the technique with respect to the target’s geometrical profile.

Providing a femtosecond optical pulse with a proper transverse spatial profile represents a fast and relatively simple method to force a quantum system to follow a prescribed temporal evolution. In the present work, we show that the quantum system presents a surprisingly high sensitivity with respect to the spatial shape of the pulse. We discuss an explicit example where differences on the order of a few nanometers in the initial pulse’s spot size induce completely different responses in the system under study.

A method of determining a structure parameter of a target on a substrate is disclosed. Illuminating a first region of the target with a first beam of coherent radiation and measuring a diffraction intensity pattern. Shifting the relative position between the target and the projection system to offset a second region to be illuminated from the first region. Illuminating the second region, offset from and overlapping with the first region, and measuring a diffraction intensity pattern. Repeating until the whole portion of interest of the target has been illuminated once, with adjacent illumination spots having some physical overlap. Retrieving phase information from the measured intensity patterns. Modeling the target to calculate a modeled diffraction intensity pattern and modeled phase information. Determining the structure parameter of the target by comparing the measured diffraction intensity patterns and the retrieved phase to the calculated modeled diffraction intensity pattern and the modeled phase information.

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.

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, qs 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.

Supported by the European Commission and EURAMET, a consortium of 10 participants from national metrology institutes, universities and companies has started a joint research project with the aim of overcoming current challenges in optical scatterometry for traceable linewidth metrology. Both experimental and modelling methods will be enhanced and different methods will be compared with each other and with specially adapted atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurement systems in measurement comparisons. Additionally novel methods for sophisticated data analysis will be developed and investigated to reach significant reductions of the measurement uncertainties in critical dimension (CD) metrology. One final goal will be the realisation of a wafer based reference standard material for calibration of scatterometers.

It was predicted a few years ago that a medium with negative index of refraction would allow for perfect imaging. Although no material has been found so far that behaves as a perfect lens, some experiments confirmed the theoretical predictions in the near-field, or quasi-static, regime where the behaviour of a negative index medium can be mimicked by a thin layer of noble metal, such as silver. These results are normally attributed to the excitation of surface plasmons in the metal, which only leads to the restoration of p-polarized evanescent waves. In this work, we show that the restoration of s-polarized evanescent waves and, correspondingly, sub-wavelength imaging by a single dielectric slab are possible. Specifically, we show that at λ = 632 nm a thin layer of GaAs behaves as a superlens for s-polarized waves. Replacing the single-metal slab by a dielectric is not only convenient from a technical point of view, it being much easier to deposit and control the thickness and flatness of dielectric films than metal ones, but also invites us to re-think the connection between surface plasmon excitation and the theory of negative refraction.