Bessel beam array generation using an axicon lens and grating

Arrays of non-diffractive beams, such as Bessel beams, are important for applications in emerging fields of microscopy, photonics, nonlinear optics, optical trapping, beam shaping, laser fabrication, etc. Our study focused on the generation of an array of zero-order Bessel beams, primarily using passive optical elements, i.e., an axicon lens, telescope, and a nanosecond laser-fabricated grating. At first, one-dimensional and two-dimensional gratings of periods in the range of 120 to 800 µm and a fill factor of 0.5 were fabricated using a diode-pumped solid-state nanosecond pulsed laser with a central wavelength of 1064 nm, a nominal pulse width of 2 ns, and a maximum pulse energy of 1 mJ. The efficacy of thus-fabricated gratings in generating a Bessel beam array was then evaluated using a beam imaging setup. To do so, a Gaussian laser beam with a central wavelength of 532 nm was incident on thegrating, followed by an axicon lens and a telescope, to generate an array of micro-Bessel beams. The generated Bessel beam array was then characterised by a 4f imaging system. The radial beam profiles of micro-Bessel beams were recorded all along the beam propagation direction and were subsequently processed using MATLAB software. The retrieved physical characteristics of Bessel beams generated with an axicon only (i.e., without grating) are as follows: Bessel central core FWHM of 0.9 µm, longitudinal FWHM of 220 µm. When gratings were employed, diverging Bessel beam arrays of dimensions up to [5 x 5] were obtained. After a certain propagation distance, depending on the period of grating, zero- and first-diffraction-order Bessel beams in the array emerged, with visible Bessel characteristics. It was also observed that the characteristics of Bessel beams in an array format remained invariant from isolated Bessel beams.