Pseudo-Bessel Beams in Millimeter and Sub-Millimeter Range

Abstract

In 1987, Durnin firstly discovered a class of novel solutions of the free-space scalar wave equation for beams that are diffraction-free (Durnin, 1987). This means that the timeaveraged intensity pattern is unchanged in the cross-section when such beam propagates in free space (McGloin & Dholakia, 2005). It is Bessel beams that are the one most interesting family of diffraction-free beams. The transverse intensity distributions of ideal Bessel beams can be highly localized, and therefore they have many unique properties, such as large depth of field, propagation invariant and reconstruction (MacDonald et al., 1996; Bouchal et al., 1998) and so on. Unfortunately, the ideal Bessel beams can not be exactly generated, due to their infinite lateral extent and energy (Monk et al., 1999). Only their approximations known as the near or pseudo-Bessel beams can be obtained physically (Bouchal, 2003), but they can still propagate over extended distances in a diffraction-free manner (Arlt & Dholakia, 2000). In optics they could have prospective applications, such as optical alignment, interconnection, and promotion of free electron laser gain (Li et al., 2006), and they may be useful in power transmission, communications and imaging applications (Mahon et al., 2005) in millimeter and sub-millimeter range. Therefore, much attention has been paid to this subject, and numerous papers have been devoted to the generation and applications of Bessel beams. More recently, the studies of Bessel beams at millimeter and sub-millimeter wavelengths have been carried out in our group. The main aim of this chapter is to present our investigation results comprehensively, including their theories, generation, propagation and potential applications. The relevant contents are organized as follows. Section 2 gives the scalar and vector analyses of Bessel Beams. How to produce pseudo-Bessel beams is described in Section 3 and 4. The comparison of propagation distance between apertured Bessel and Gaussian beams is made in Section 5. Lots of potential applications are discussed in the last Section 6. 24