研究了飞秒激光诱导单个空气等离子体通道的吸收和辐射特性,给出了等离子体通道吸收系数的解析表达式,并理论推导出了辐射能流率的表达式。与TOPS不透明度数据库查表方法比较,两种方法计算结果符合得很好。分析了吸收和辐射参量对入射激光参量的依赖关系。计算了中心波长800 nm,脉宽40 fs的飞秒激光空气等离子体通道的吸收和辐射参量的典型数值。结果表明,成单丝情况下等离子体通道的Rosseland吸收系数为0.0270 cm-1 ,辐射能流率为7.87×1010 W/m2;窄脉宽长波长的入射激光有利于生成吸收小辐射强的等离子体通道。

The absorption and emission characteristics of single plasma channel produced by femtosecond laser pulse in air have been investigated theoretically. Analytical expressions of Rosseland mean absorption coefficient and radiant energy fluence rate are deduced. It is found that our analytical results are consistent with data from TOPS opacities database. The dependences of absorption and emission characteristics on initial laser parameters are studied. Calculation of such quantities for air plasma channel induced by laser pulse with 800 nm central wavelength and 40 fs pulse width is carried out. Results indicate that,in the case of single filament,the average Rosseland mean absorption coefficient is 0.0270 cm-1,and total radiant energy fluence rate reaches 7.87×1010 W/m2. Incident fs laser with shorter pulse width and longer wavelength furns out advantage to producing weak absorbing and strong radiative plasma channel.