| Abstract [eng] |
One of the challenges for the laser micromachining technologies is the beam shape and its longitudinal profile, which makes a huge impact for the result of the process. Airy beam is a unique beam shape, because its Rayleigh length is a few times longer compared to a Gaussian beam. Also, its intensity peak travels along a curved trajectory during the propagation. Curved trench machining is proved to be possible using Airy beams. However, machining of asymmetric modifications in a transparent material bulk has not been demonstrated. Hence, the aim of this work is to generate Airy beams using a few different methods and measure the weight of parameters. Finally, to induce asymmetric modifications in transparent material bulk using the Airy beam. First optical system for a beam shaping was based on a spatial light modulator. In a spatial light modulator, the phase retardance is induced and controlled by means of an electric field due to the birefringence of liquid crystals. Second optical system for a beam shaping was based on geometric phase gratings. In geometric phase gratings, phase retardance is induced by space-variant self-assembled form birefringence in fused silica glass. It has been determined, that when the coefficient of the phase mask for Airy beam generation increases, the curvature of the trajectory of an intensity peak decreases. Herewith, the smaller the curvature, the longer the trajectory. Using the same parameters, an Airy beam generated by a geometric phase grating has a smaller curvature, compared to an Airy beam generated by a spatial light modulator. The main problem when generating Airy beams using both optical systems is the undiffracted zero order beam, which interferes with an intensity peak of a diffracted Airy beam. Experiments show that combining phase masks for Airy beam generation with linearly-variant and quadratically-variant phase masks induce displacement of an Airy beam transversely and longitudinally, respectively. The larger the displacement is, the bigger the intensity of the undiffracted zero order beam becomes, and less diffraction occurs. Finally, asymmetric modifications in VIOSIL type synthetic quartz glass substrates were induced using ultrashort Airy beams generated by geometric phase gratings. The ratio of a transverse shift of the modifications to the length of the modifications of 0,08 has been demonstrated. |
