Millimetre-wave Bessel beams using computer holograms

Abstract

A computer-generated binary amplitude hologram is used to transform an initial Gaussian electromagnetic field with spherical phase front at 310 GHz into a non-diffracting Bessel beam. The beam profile is measured with the help of a near field scanner. In contrast to the situation in the optical region, both amplitude and phase information is readily obtainable from the generated field.

Nonlinear localization of light

“…In acoustics, localized sound waves are desirable for enhanced resolution in ultrasonic imaging, and interestingly, linear X waves in acoustics were demonstrated 5 years earlier than in optics [71]. Propagation of localized microwaves over distances of tens of wavelengths [72], as well as preliminary experiments in localization of terahertz radiation [73] and radio waves [74] had been reported to date. Conical waves are well known in astrophysics -a light from distant objects, distorted by gravitational lenses is transformed into a conical wave, which carries the information not accessible by other means (because of limited angular resolution, for instance) about the object as well as about the structure of the Universe [75].…”

Pseudo-Bessel Beams in Millimeter and Sub-Millimeter Range

“…However, at millimeter and sub-millimeter wavebands, only two methods of production Bessel beams have been proposed currently, i.e., axicon (Monk et al, 1999) and computer-generated amplitude holograms (Salo et al, 2001;Meltaus et al, 2003). Although the method of using axicon is very simple, only a zero-order Bessel beam can be generated.…”

Quasi-Optical Bessel Resonator

“…Examples can be found in [7,8,[12][13][14][15][16]. To our knowledge, no active schemes have been reported at these wavebands as yet.…”

“…Numerous approaches to generate pseudo Bessel beams have been suggested, which can be sorted roughly into two classes [3][4][5], i.e., passive and active schemes. The first class uses the spatial filter to transform an incident beam into an approximation to Bessel beam, such as narrow annular slit [2], computer-generated holograms (CGHs) [6][7][8], Fabry-Perot cavity [9], optical refracting systems [10], axicon [11][12][13][14] and diffractive phase elements (DPEs) [15][16][17]. The other class is formed by methods relying on a resonator frame to produce the Bessel-type modes.…”