Study Of Direct Writing Of Expanded-core Waveguide And Surface Micro-channels In Glass By Ultrashort Pulse Laser

With the development and maturity of ultrashort pulse laser systems in recent decades,various research works have been carried out rapidly in the field of ultrashort pulse laser micro-nano machining.Fruitful achievements have been fulfilled in this domain.Specifically in the field of 3D additive manufacturing that based on multiphoton photopolymerization or laser induced forward transfer techniques etc.;or in applications of material cutting,drilling,heterogeneous welding,surface cleaning,laser induced periodic surface structure etc.that based on ultrashort pulse laser ablation?removal of material?;When ultrafast laser pulse with appropriate energy dose was focused inside a transparent medium,due to nonlinear absorption,material modification?refractive index modification?would occur in a localized region near the foci,which opens the venue for direct writing of optical waveguides or more complicated photonic devices.In the frame of ultrashort pulse laser micro-nano machining,this dissertation concentrates predominately on experimental research in two subjects:direct writing of expanded-core waveguide in various of glassy substrates;and surface micro-channel fabrication in fused silica.The main work and innovations of this dissertation are listed as following:1.We propose a method for fabricating the expanded-core waveguide?ECW?with single-mode and large mode area using femtosecond laser direct writing technology.The characteristics of ECW are theoretically analyzed.ECW and ECW based Y-type beam splitters are experimentally realized in fused silica glass.The single-mode ECW characterizes a mode field diameter of?30?m and a propagation loss of?0.1dB/cm.2.A Type I single-core waveguide is written in Yb³⁺doped phosphate glass,then a waveguide laser with an output up to 11 mW and a slope efficiency of 2%is realized at the wavelength of 1029 nm;The ECW concept is extended to the Yb³⁺doped phosphate glass,which effectively improves the processing efficiency of the photonic waveguide device.A single-mode operation ECW is obtained with a mode field diameter more than 3 times than that of the single-core waveguide.This lays the foundation for realizing power scaling single-mode waveguide laser.3.The characteristics of zeroth-order Bessel beam and how a few factors?i.e.wave amplitude,phase distortion and non-collimation of the incident beam?would impact on the Bessel beam are numerically studied in Matlab.4.Single-shot Gaussian-Bessel laser beams are used for drilling micro-channels on front side of fused silica in ambient condition.Optimized energy conditions are defined typically corresponding to the use of^micro-Joule pulse energy for 1 ps pulse duration.Non-tapered channels with mean diameter of?1?m and length of?40?m while maintaining an utmost quality of the front opening of the channels are fabricated.These results open promising prospects for structuring material surface with moderate aspect ratio in the micrometric domain.5.Scalar Fresnel diffraction based numerical simulation is performed to evaluate the axial intensity profiles of the truncated Bessel beams according to different annular slit widths.Parameter optimization of the truncated Bessel beam is experimentally carried out during the micro-channels fabrication.By scanning the processing parameters,micro-channels with diameter from?300 nm to?2?m and length from?1?m to?30?m are achieved with effective control.This shows the potential of truncated Bessel beams in developing new fabrication routes at the spatial scale below?m and low aspect ratio,which is suitable for photonic crystal application and meta-materials in general.