A “Bessel beam” is a special type of laser output that appears as a bright spot surrounded by concentric rings. This type of beam has found utility in applications such as industrial micromachining, microscopy and optical micro- manipulation. Bessel beams have the distinct properties of not spreading out as they propagate and having the ability to reform themselves after encountering an obstacle. The capability to modify the properties of a Bessel beam as it propagates would increase the flexibility and potential usefulness of these beams. At present, available techniques to change the propagation properties of a Bessel beam require expensive optical devices or complicated experimental procedures.
Our project explored alternative, simple and inexpensive techniques to modify Bessel beams based on using fluids and elastomers.
We found that, by having a Bessel beam pass through different combinations of fluid layers, the intensity profile of the beam, including the diameter of the bright central spot, could be changed. Ms. Dina Palangyos, the research assistant for the project, is analyzing the mechanism of this fluid-based modification of Bessel beams for her PhD dissertation. A second component of the project employed copying microscopic structures on the surface of a beetle carapace onto a transparent elastomer. Beams that have the appearance of Bessel beams can be generated by passing a laser beam through the elastomeric replica. Ms. Michie Vianca De Vera reported these results in her undergraduate thesis and presented a paper at an international conference.
Bessel beams modulated by various fluid layers are shown here:
In the image below, a beam similar to a Bessel beam (top) is generated by an elastomeric replica of a beetle carapace (bottom):
Michie Vianca D. De Vera, Raphael A. Guerrero, “Diffraction from elastomeric replicas of Philippine weevil surface features,” Proc. SPIE 11481, Light in Nature VIII, 114810H (21 August 2020)