Investigation Of Femtosecond Laser Direct Writing Transparent Dielectrics

The width of the femtosecond laser pulse is very short,and the focused femtosecond laser pulse can reach high enough peak intensity and cause nonlinear absorption with the material,so it can be used to generate nanostructures on the surface or inside the transparent medium.In recent years,the femtosecond laser direct writing technology has developed rapidly.It can produce various micro-optical components on the surface and inside of transparent materials,which greatly promotes the development of integrated optics.In this paper,we studied the micromachining process of femtosecond laser direct writing transparent dielectrics,and analyzed the interaction process between femtosecond laser and transparent dielectrics.This paper includes the following two parts:1.Femtosecond laser with repetition frequency of 500 k Hz was used to induce microstructures by line scanning and raster scanning on the surface of soda lime silicate glass.The influence of femtosecond laser processing parameters on the surface morphology of the modified zone was analyzed.A nanocluster-ripple grating can be fabricated with appropriate laser energy,scan velocity and scan line spacing.The ripple region acts as the groove of a grating and the nanocluster region serves as the separation region between two neighboring grooves.The grating period can be very small because we do not need to remain an unmodified region as a gap between two adjacent laser modified regions to compose a grating.Our experimental results demonstrate that the scan line spacing plays an important role in the diffraction efficiency of the fabricated grating.According to the influence of processing parameters on the surface topography,we fabricated different period gratings which were used as Terahertz polarizers to verify the effect of wave polarization modulation performance.2.Femtosecond laser with repetition frequency of 500 k Hz was used to induce selective etching on the surface of soda lime silicate glass and inside the fused silica.For the soda lime silicate glass,we experimentally studied the influence of the surface morphology on laser pulse energy and the etching time.The line width and depth of the laser modified region after selective chemical etching was measured,which provided reference data for making smooth microchannels on the surface of the material.Then,we studied the influence of the selective etching speed in fused silica glass on laser polarization,single pulse energy and scanning speed.The main factors affecting the etching speed for the 500 k Hz femtosecond laser were discussed,which effectively improves the process efficiency of the selective femtosecond laser induced selective chemical etching process.