Research On Infrared Grating Processing Technology Based On Femtosecond Laser

The use of femtosecond lasers for the preparation of microstructures on material surfaces has been a hot research topic in the field of processing.At present,femtosecond laser processing is widely used in precision processing,integrated circuits and other related fields,where it is mainly used to process various optical components,especially the preparation of gratings.The use of femtosecond laser for the preparation of grating structures has the advantages of high processing rate,simple processing process,and high processing accuracy.In view of the incomplete research on the processing technology of infrared grating by femtosecond laser,in this article,the optimal processing process of infrared grating structure by femtosecond laser in monocrystalline silicon from the direction of the mechanism of laser-material interaction.The major work and results of this article are as followed:(1)The interaction mechanism between the femtosecond laser and metal and semiconductor silicon is investigated,and the semiconductor silicon dual-temperature equation is studied on the basis of the conventional metal dual-temperature equation for analyzing the surface microscopic action process and influence of the zone fused single-crystal silicon under the action of the femtosecond laser.Through simulation modeling and numerical analysis,the role of the femtosecond laser in the zone fused single crystal silicon material is explored,and it is concluded that the variation law of temperature when electrons and lattice reach equilibrium increases with the increase of laser energy density.The feasibility of femtosecond laser processing of microstructures on semiconductor silicon surfaces is theoretically illustrated.(2)The design of subwavelength infrared grating structure is carried out by using the finite element analysis method,and the structural model of subwavelength infrared grating is constructed to investigate the influence law of different infrared grating structure parameters(period,height,duty cycle)on the optical properties of the material.The simulation results show that: the period,height and duty cycle of the subwavelength infrared grating are important factors influencing the antireflection of silicon materials in the infrared band,among which the period of the grating structure is the main influencing factor to achieve the antireflection effect;controlling the period and duty cycle of the grating structure can achieve the antireflection effect in a specific band;meanwhile,the antireflection effect of the structure can be further optimized by regulating the grating height.The subwavelength infrared grating structure with a period of 6 μm,duty cycle of 0.6 and height of 3.3 μm was finally determined,and the average transmittance in the far infrared band(20～24 μm)reached 98%.(3)In this article,using femtosecond laser direct writing processing technology,the influence law of femtosecond laser processing process parameters on the surface structure morphology of single crystal silicon is investigated,and the processing process of subwavelength infrared grating structure preparation is obtained.The experimental study investigated the femtosecond laser grooving process on the surface of zone fused single crystal silicon,and the influence of different femtosecond laser processing parameters on the surface shape and morphology of the groove structure on the single crystal silicon surface was investigated.Further orthogonal experiments were carried out to investigate the comprehensive influence of multi-factor conditions on the surface processing effect under the designed grating structure parameters,and the laser power was determined to be the main influencing factor on the groove width,depth and roughness through the extreme difference analysis,and the best processing solution was derived within the adjustable parameters.The experimental results can provide the experimental basis and technical support for femtosecond laser processing of infrared grating structures.The optimal processing parameters of the infrared grating structure by femtosecond laser were finally determined as follows: laser power 46mw;laser scanning speed 10mm/s,laser scanning times 3 times.The parameters of the IR grating structure prepared by this parameter are close to the simulated design shape,with good structural uniformity and high processing efficiency.(4)The square-shaped subwavelength grating structure was prepared on the surface of the zone fused single crystal silicon based on the obtained processing parameters,and the transmittance of the prepared subwavelength grating structure was tested.The results show that the prepared infrared grating structure has 77% transmittance in the far-infrared band(20～24μm)with obvious anti-reflection phenomenon,which verifies the validity of the simulation model and the feasibility of the femtosecond laser direct writing process.