Non-diffraction-length, tunable, Bessel-like beams generation by spatially shaping a femtosecond laser beam for high-aspect-ratio micro-hole drilling

Abstract

Bessel beams are advantageous in high aspect-ratio microhole drilling because of their immunity to diffraction. However, conventional methods of generating Bessel beams result in poor adjustability of the nondiffraction length. In this study, we theoretically describe and experimentally demonstrate the generation of Bessel-like beams (BLBs) with an adjustable nondiffraction length by using a phase-only spatial light modulator. In this method, nondiffraction lengths varying from 10 to 35 mm can be achieved by changing the designed phase profile (curvature). High-quality, high aspect ratio (560:1) and length-adjustable microholes can be drilled by spatially shaping a femtosecond laser beam.

Lens-axicon separation to tailor aberration free focused Bessel-Gaussian beams in the paraxial regime

“…Although we have not presented the study of the ring formed at the focal plane, the model confirms the results shown in [19] where the lens-axicon separation can be used to modify the ring size. The results presented can be implemented in any instrument capable to modulate phase as for instance SLMs [5].…”

“…As such, these approximated Bessel beams are known as quasi-Bessel beams or Bessel-Gaussian beams [4]. A common way to generate Bessel-Gaussian beams is with an axicon, although it can also be engineered using a range of experimental techniques including diffractive optics, computer generated holograms, spatial light modulators (SLMs) [5] and other optical elements [6]. Roughly, the design of the Bessel-Gaussian beam can be controlled by the apex angle of the axicon that accounts for the width of the central spot, while the Gaussian beam width controls the axial length where the beam can be well approximated by a Bessel function.…”

“…Additionally, in the implementation of Bessel-Gaussian beams the role of aberrations can completely distort the final result. All these elements are essential in any practical implementation of Bessel beams, but are particularly important in those applications where the power of the central core and the light field distribution have to be precisely controlled, such as optical trapping [10,11], non-linear optics [12] and photo-patterning [5,13]. In order to manipulate the peak intensity and the Bessel zone length, lens-axicon doublets have been proposed.…”

Inhibition and enhancement of linear and nonlinear optical effects by conical phase front shaping for femtosecond laser material processing

“…Iterative methods provide flexible means for optimizing the shape of lab-on-a-chip sub-components 31 while accelerated beams 32 offer 3D shaping of curved trenches. Alternatively, elongation of the interaction volume into a filament shape is attractive for forming vertical waveguides 33 , stresscleaving arrays 17,34 , and thick welding 35 seams while Bessel-like beams [36][37][38][39] with high aspect ratio are useful for high speed cutting of glass 40 , or opening of long and narrow holes in glasses 11,41 , and polymers 38 .…”

Truncated Gaussian-Bessel beams for short-pulse processing of small-aspect-ratio micro-channels in dielectrics

“…Beam filtering at the Fourier plane of a 4f optical system with a stopper and aperture efficiently suppresses the undesired axial modulation [23]. The axial intensity profile can also be customized: by using spatial light modulators that enable to engineer the beam propagation, on-axis intensities with uniform, increasing/decreasing [24,25] or length-tunable profiles [26] have been demonstrated. In the present work, we use a simple and convenient solution -near-field filtering with an annular slit -to tailor the depth of focus (DOF) of the Gaussian-Bessel beam, and we show the interests of this technique to machine short-length microchannels on the front-surface of transparent dielectric materials.…”