The last few years have seen a rapid acceleration in the field of beam manipulation [5].

Central to this expansion is the idea that the purposeful design of the beam’s wavefunction can imbue the electron with new properties that potentially enable new measurements previously impossible.

Examples of this are the orbital angular momentum possessed by electron vortex beams [1], or the reduced diffraction of Airy and Bessel beams [2-4].

In these studies, holographic reconstruction remains the most widely used method to generate new wave types due to its generality and flexibility but presents several shortcomings, chiefly the production of multiple diffracted beams [1-3,5].

Here we showcase different approaches to the production of reduced diffraction beams.

We generate Airy waves by a careful tuning of the aberration function of an aberration corrected TEM, and produce a Bessel beam by limiting the angular spread of the electrons with an annular aperture.

We study the beam propagation to prove the limited diffraction, and give experimental proof of extended depth of focus in imaging with Bessel beams.

Acknowledgements:

GG, AB and JV acknowledge funding from the European Research Council under the 7th Framework Program (FP7), ERC Starting Grant No. 278510-VORTEX.

References:

[1] J. Verbeeck et al. Nature 467, 301 (2010).

[2] N. Voloch-Bloch et al. Nature 494, 331 (2013).

[3] V. Grillo et al. Phys. Rev. X 4, 011013 (2014).

[4] R. Shiloh et al. Phys. Rev. Lett. 114, 1 (2015).

[5] G. Guzzinati et al. Ultramicroscopy 151, 85 (2015).

Figures:

(a) By carefully tuning the intensity and orientation of threefold astigmatism and coma, the cubic phase plate of the Airy beam is generated. (b) Theoretical and experimental intensity of the beam generated with this approach. (c-d) Beam propagation recovered from a focal series, showing the reduced diffraction and acceleration of the main lobe.

(a) Annular aperture for the production of a Bessel beam. (b) Experimental beam intensity. (c) Reduced diffraction propagation of the beam over a range of 7 µm. (d) comparisone between the propagation of the Bessel beam and a conventional beam.

(a) Imaging a highly tilted crystal with (b) a conventional or (c) a Bessel beam. With the latter the contrast is lower but the focal range is extended, as proven by the intensity of higher fourier components in the image

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