Optimization of a constrained linear monochromator design for neutral atom beams

Kaltenbacher, T.

doi:10.1016/j.ultramic.2016.02.003

Cited by 3 publications

(3 citation statements)

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“…Researchers often use these simplified expressions to determine the beam's intensity. Over the years, amongst several existing models, often the simpler ones have been favoured, (see for example, [68,69]) despite their not being backed by strong empirical measurements nor by strong theoretical support. In the following paragraphs we review a few popular intensity models from the different families described in Sec.…”

Section: Further Approximationsmentioning

confidence: 99%

“…To date, there are four papers that aim to optimise the microscope design using a theoretical framework for the intensity. The first paper from 2016, written by Kaltenbacher [69] proposes a multi-objective optimisation approach to optimise a microscope composed of a pinhole and two zone plates. Unfortunately, Kaltenbacher does not consider the dependency of the intensity with the skimmer radius which is known to be crucial in the case of zone plate microscopes, rendering his approach unphysical in terms of the intensity.…”

Section: Optimal Microscope Configurationsmentioning

confidence: 99%

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Neutral Helium Microscopy (SHeM): A Review

Palau¹,

Eder²,

Bracco³

et al. 2021

Preprint

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Neutral helium microscopy, also referred to as scanning helium atom microscopy and commonly abbreviated SHeM, is a novel imaging technique that uses a beam of neutral helium atoms as an imaging probe. The technique offers a number of advantages such as the very low energy of the incident probing atoms (less than 0.1 eV), unsurpassed surface sensitivity (no penetration into the sample bulk), a charge neutral, inert probe and a high depth of field. This means that fragile and/or non-conducting samples can be imaged as well as samples with high aspect ratio, with the potential to obtain true to scale height information of 3D surface topography with nanometer resolution. However, for a full exploitation of the technique, a range of experimental and theoretical issues still needs to be resolved. In this paper we review the current state of research in the field. We do this by following the trajectory of the helium atoms step by step through the microscope. From the initial acceleration in the supersonic expansion used to generate the probing beam over the interaction of the helium atoms with the sample (contrast properties) to the final detection and post-processing. We also review recent advances in scanning helium microscope design and we present an overview of the samples that have been investigated with SHeM up till now.

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Section: Further Approximationsmentioning

confidence: 99%

Section: Optimal Microscope Configurationsmentioning

confidence: 99%

Neutral Helium Microscopy (SHeM): A Review

Palau¹,

Eder²,

Bracco³

et al. 2021

Preprint

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show abstract

“…a multi-objective optimisation approach to design a complex atom optics setup involving two zone plates and a pinhole [13]. Kaltenbacher has used large approximations for the intensity and size of the beam, and using a multi-objective optimisation leads to Pareto-optimal solutions rather than direct solutions for a specific resolution.…”

Section: Introductionmentioning

confidence: 99%

A method for constrained optimisation of the design of a scanning helium microscope

et al. 2019

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We describe a method for obtaining the optimal design of a normal incidence Scanning Helium Microscope (SHeM). Scanning helium microscopy is a recently developed technique that uses low energy neutral helium atoms as a probe to image the surface of a sample without causing damage. After estimating the variation of source brightness with nozzle size and pressure, we perform a constrained optimisation to determine the optimal geometry of the instrument (i.e. the geometry that maximises intensity) for a given target resolution. For an instrument using a pinhole to form the helium microprobe, the source and atom optics are separable and Lagrange multipliers are used to obtain an analytic expression for the optimal parameters. For an instrument using a zone plate as the focal element, the whole optical system must be considered and a numerical approach has been applied. Unlike previous numerical methods for optimisation, our approach provides insight into the effect and significance of each instrumental parameter, enabling an intuitive understanding of effect of the SHeM geometry. We show that for an instrument with a working distance of 1 mm, a zone plate with a minimum feature size of 25 nm becomes the advantageous focussing element if the desired beam standard deviation is below about 300 nm.

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