Experimental Study On High Efficiency Direct Writing Micro/nano Structures By Femtosecond Laser Bessel Beam

Femtosecond(fs)laser micro/nano fabrication technology with the characteristics of non-contact,high precision,flexible and controllable,has become one of the research focuses in the field of micro/nano manufacturing technology and the high efficient fs laser direct writing has attacted more and more attention.Based on the spatial light shaping for Bessel beams,small diameter,high-aspect-ratio and high quality micro/nano structures were fabricated by single pulse processing.At present,it was difficult to balance these two aspects of the structures fabricated by Bessel beams with the minimum diameter and large area efficient processing.The piezoelectric ceramic micromobile device or linear motor driven platform was commonly used for machining large area micro/nano structures,the frequent acceleration or deceleration of system inertia had to be overcomed in the point by point scanning process.It was hard to achieve high efficiency fabrication,and seriously restrict the large area the micro nano structure preparation and application.In order to overcome these above problems,an optimization strategy of the on-the-fly drilling method was put forward to improve the machining efficiency of large area,that is,the efficient processing of the large area micro/nano structure can be realized by the single-pulse fs laser Bessel beam.Meanwhile,a spatial light modulator was ultilized to divide a laser beam into multiple beams,which was a multispot parallel efficient processing method.On this basis,the four application examples of femtosecond laser beam Bessel efficient micro/nanomachining were explored,including: 1)periodic hierarchical micro/nano silicon surface structures;2)controllable micro/nano silicon structures;3)concentric polycyclic silicon surface microstructures;4)high-aspectratio microholes array.The main research content of this paper was divided into the following four parts:1.Combined with anisotropic etching and metal assisted etching of silicon,the method for using femtosecond laser beam Bessel periodic dynamic scanning was ultilized to efficiently fabricate hierarchical micro/nano grating structures,and the different surface morphologies and widths were controlled by adjusting the laser pulse energy and chemical etching time.Moreover,by using the spatial light modulator to change the phase of the laser beam,a multi beam is shaped by a laser beam,and the processing efficiency was improved greatly.2.Large areas of controllable silicon surface micro/nano structures array with different morpgologies and diameters were fabricated by chemical etching assisted femtosecond laser pulse Bessel printing.And the influence of laser pulse energy and chemical etching time on the surface morphology of silicon structures was studied in detail.We found that the specific <100> singlecrystal silicon sample was transformed from single-crystalline(c-Si)into amorphous silicon state(a-Si)after single-pulse fs laser beams irradiation and the chemical activity of laser irradiated area decreased significantly,which can be used as a etching mask in KOH etching solution.And maskfree fabrication by single-pulse fs laser was then realized.The size of the surface structures from nano scale(~313 nm)to micron(~1.91 μm)within a wide range of different morphologies can be precisely controlled by tuning the laser pulse fluence.3.A new method for the high efficiency machining of concentric ring structures on silicon surface was proposed,which was based on the Bessel beam single pulse irradiation assisting chemical etching.After single-pulse Bessel beams irradiation,concentric ring modified zone with higher chemical activity was formed,and it was selectively removed by acid etching solution in etching process.Meanwhile,the experimental results showed that the number of rings with concentric ring structure had a direct influence on the laser pulse fluence and the focal plane position.4.The aspect ratio of taper-free microholes srilled by single-pulse Bessle beams was 52 times larger than that achieved by using Gaussian beams in similar focousing conditions.The diameter and aspet ratio of microholes was 1.58μm and 330:1,respectively.Meanwhile,the high quality,high aspect ratio and uniform microholes array with the area of 1 cm × 1 cm was obtained in only 42 minutes.From the point of view of the experimental observation,the intensified charge-coupled device(ICCD)imaging system was ultilized to observe the plasma ejection process in the microholes machining processing.For single-pulse Bessel beams microdrilling,the filamentary plasma plume can be formed inside the materials in a certain time.Thus,microdrilling such thin,long,uniform microholes with single-pulse Bessel beams was attributed to electron density control by spatially shaping femtosecond laser pulses.