Diffraction is a fundamental property of light propagation. Owing to thisphenomenon,light diffracts out in all directions when it passes through asubwavelength slit.This imposes a fundamental limit on the transverse size of alight beam at a given distance from the aperture. We show that asubwavelength-sized beam propagating without diffractive broadening can beproduced in free space by the constructive interference of multiple beams of aFresnel source of the respective high-refraction-index waveguide. Moreover, itis shown that such a source can be constructed not only for continuous waves,but also for ultra-short (near single-cycle) pulses. The results theoreticallydemonstrate the feasibility of completely diffraction-free subwavelength-beamoptics, for both continuous waves and ultra-short pulses. The approach extendsoperation of the near-field subwavelength-beam optics, such as near-fieldscanning optical microscopy and spectroscopy,to the "not-too-distant" fieldregime (0.5 to about 10 wavelengths).
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