The term “non-diffracting Bessel beam” refers to a specially engineered optical beam that does not change its intensity profile on propagation. This idea is somewhat counterintuitive as most optical beams are expected to spread out as they propagate. Non-diffracting beams are known in Optics literature for over 30 years, e.g., those having profiles described mathematically by Bessel or Airy functions. While most literature on non-diffracting beams treats the problem using scalar diffraction theory (where only one scalar component of linearly polarized light beam is assumed), the present work for the first time introduces a new class of non-diffracting beams which have variable polarization state while maintaining the intensity profile. A non-spreading beam has interesting applications, e.g. in (1) free space communications where non-spreading property of beam means efficient transmission to a far-away receiver, (2) microscopy and optical tweezing where a non-diffracting beam can maintain tight focus over longer depths, and also in (3) material processing applications such as direct laser writing of three-dimensional photonic structures. The additional degree of variable polarization added to the mix can open up several new avenues in these application areas that will surely be explored in near future.
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