单光束飞秒激光诱导的电子态密度分布对双周期纳米光栅的影响

Influence of Electron Density Distribution Induced by Single Beam Femtosecond Laser on Doubly-Periodic Nanogratings

研究了不同脉冲能量下1kHz飞秒激光脉冲在石英玻璃内部诱导的损伤痕迹、纳米光栅结构及其双折射特性,发现在激光辐照区域顶端形成的微纳结构具有两种周期性:沿光传输方向的周期为ΛK;沿激光偏振方向的周期为ΛE.通过数值模拟飞秒脉冲在石英玻璃内部的传输过程,研究了入射能流密度分布及自由电子密度分布对双周期纳米光栅结构的影响.结果表明,较大的入射能流密度有利于纳米光栅的形成,且产生的电子密度会影响周期ΛK,电子密度越大,周期ΛK越大.从理论上分析了双周期纳米光栅结构的形成过程,认为等离子体非对称生长及其引起的局域场强分布影响了双周期纳米光栅结构的形成.

The characteristics of nanogratings including damage trace,structure and birefringence properties,which are induced in fused silica by 1kHz femtosecond laser pulses with different pulse energy,are studied.Two different periodic nanostructures are observed at the top of laser irradiation area,the primary structure with the periodΛKin the direction of light propagation and the secondary structure with the periodΛEin the direction of laser beam polarization.The influence of incident energy flux density distribution and free electron density distribution on doubly-periodic nanogratings is investigated by numerically simulating the propagation process of femtosecond laser pulses inside the fused silica.The results show that higher incident energy flux density benefits the formation of nanogratings,and the generated electron density influences the periodΛK.The higher the electron density is,the longer the periodΛKis.The formation of doubly-periodic nanogratings is analyzed theoretically according to current experimental results.The asymmetric growth of plasma and the causing local intensity distribution affect the formation of doubly-periodic nanogratings.