Generation of multiple parallel non-diffractive beams without any disruption of each beam is a challenging task. Here, we report the approach of spatial-spectral modulation for non-disruptive generation of Bessel beam array. Such modulation is realized with a simple beam splitter placed in a Fourier plane of the initial beam. The various designs of the beam-splitter phase mask allow to generate an array of the Bessel beams with various shapes and controlled intensity distribution without mutual interference of each beam. As such, this array formation can enhance quality of glass cutting and increase the throughput of micro-patterning of glass-fine mask required for a new generation high-resolution OLED display.
Requirements on glass manufacturing with exceptionally high mechanical strength triggered development of new laserbased processing methods. Localized modifications produced by ultrashort pulsed lasers are attractive but may lead to micro-crack generation in glass. Aiming to control stresses during volumetric material modifications, we have studied the effect of pulse duration experimentally. Bessel beam shapes with arbitrary conical angles have been generated using a programmable spatial light modulator (SLM), while stresses have been monitored using time-resolved optical transmission and cross polarized microscopy. Pulse duration variation influences mechanical stress in the laser glass interaction, and we found the optimized pulse duration exists in the laser glass machining by pump-probe microscopy.
Diffraction-free Bessel beams have been of great interest for laser processing of transparent materials. Compared to traditional Gaussian beams, the Bessel-Gauss beams has thin focus profile which remains invariant over much longer propagation distances. Achieved in such a way extended depth of focusing in combination with precise energy deposition has opened diverse promising applications in display industry. Here we have analyzed the effect of conical angle on the interaction of Bessel beam with a display panel having multiple organic and inorganic layers on a glass. First, we have shown that experimentally observed thermal damages in display emission area are caused by long Bessel beam tails in contrast to Gaussian beams, where the damages are driven by heat diffusion. Second, we study the role of Kerr effect and arising instabilities in non-linear propagation through the glass substrate. Using numerical simulations and in-situ pump-probe microscopy methods we gain the knowledge of primary steps of energy deposition with high temporal and spatial resolution. At high laser intensities and low numerical aperture, the original Bessel beam profile can be de-stabilized leading to the longitudinal fluctuation of intensity. The laser processing with high conical angle Bessel beams is much more resistant to undesirable beam self-focusing and phase self-modulation effects, which enables us to achieve the regime of optimal laser energy deposition for high-quality glass cutting.
To examine the ablation dynamics of silver thin films by femtosecond laser, we experimentally investigate the plume evolution and behavior of ejected nanoparticles (NPs) via emission and scattering spectroscopy measurements under background pressures of 760 torr, 5 torr, 5 x 10-3 torr, to 3 x 10-5 torr. The emission spectroscopy experiments show that the propagation of the ablated plume is affected by ambient pressure. The higher the pressure, the more the propagation of the plasma is suppressed. Under higher vacuum, the lifetime of plasma is shorter due to diminished collisions with background molecules. The evolution of plasma lasts more than 200 ns under 760 torr while it does not exceed 200 ns under high vacuum (3 x 10-5 torr). Through the scattering measurements, the average propagation speed of NPs is 200 m/s under 3 x 10-5 torr, 190 m/s under 5 x 10-3 torr, 155 m/s under 5 torr, and 120 m/s under 760 torr. The ejected nanoparticles from the periphery of the ablated spot exhibit oblique trajectories because of the exerted recoil pressure at the spot center region that is subject to high incident energy densities.
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