Tuning Bessel beam propagation properties with liquid media
Techniques for optical trapping and micromanipulation, as well as precision drilling, have resulted from the ability to generate different types of Bessel beams. A standard method for producing Bessel intensity profiles involves an annular slit and focusing lens. The fixed geometry of this optical system only allows the generation of a particular Bessel beam with specific propagation properties. To increase the flexibility of a conventional annulus-lens configuration, we introduce a fluid-based method for modifying the core diameter and propagation properties of zero-order Bessel beams. In our optical set-up, Bessel beams are created with a HeNe laser operating at 543 nm with an output power of 4 mW. An annular slit is placed at the front focal plane of a lens with f = 25 cm. A transparent, custom-built container composed of three fluid chambers, each 5 cm in length, is placed after the lens. Our experiments make use of two fluids: water (n = 1.33) and vegetable oil (n = 1.43). Without using any fluids, at a propagation distance of 50 cm from the lens, our set-up produces a Bessel beam with core diameter = 0.231 mm. When the beam passes through a sequence of oilair-water, the core diameter at the same distance increases to 0.241 mm. We also observe an extended maximum propagation distance for a beam that travels through this combination of media. Modification of Bessel beam propagation properties is consistent with a change in effective focal length brought about by refraction through the liquid components.
Donna H. Gabor, Raphael A. Guerrero, "Tuning Bessel beam propagation properties with liquid media," Proc. SPIE 11107, Laser Beam Shaping XIX, 1110707 (9 September 2019); https://doi.org/10.1117/12.2528680