单周期超短脉冲光束的时空传输.pdf

32 5 V ol. 32 , N o. 5 2002 10 L ASER IN FRAR ED October, 2002 #光电子技术# : 1001- 5078( 2002 05- 030 3- 0 3 王兆英, 林 强 ( , 310028 : 当电偶极子以高斯脉冲形式随时间振荡时, 辐射出的电磁场 以用来描写非缓变包络 近似条件下单周期超短脉冲光束在自由空间中的传输特性利用复点源模型, 通过分析和计 算, 我们得出它的传输特性第 一, 在空间传输过程中, 单周期超短脉冲高斯光束能流密度基 本保持高斯函数不变, 振幅大小随不同的z 平面振荡第二, 单周期超短脉冲光束在真空中主 要以光速c 沿z 方向传输在传输过程中, 脉冲宽度保持不变, 脉冲形状演变成不对称能流 密度不再随时间作简谐振荡, 它的振幅构成 一个高斯形状的包络 : 单周期脉冲; 时空演变; 高斯函数 : O43 1 :A Spatiotemporal Evolution of Single- cycle Electromagnetic Pulses WA N G Zhao-ying, LIN Qiang ( Institute of Optics, Department of Physics, Zhejiang U niversity , Hangzhou 31002 8, China Abstract:W e repor t an exact analytic solution of the M ax w ell. s equations that is capable of descr ibing single- cy cle electromagnetic pulses beyond the slo wly vary ing envelope approx imation . T he solution is based on the radiatio n f ield emitted by the oscillating electric dipoles. T he spationtemporal evolution o f single- cycle electromag netic pulses in free space is illustrated and discu ssed detailedly by using t he obtained analyt ic solution . At f irst , the instantaneous energy density of the electromagnetic pulse keeps in Gaussian shape during the propag ation in space, but the amplitude oscil- lates w it h the propagation distance. Secondly, the single- cycle electro magnetic pulse propagates mainly along z- axis at the speed of c. During the propagation , the pulse w idt h and pulse shape keep invar iant . T he instantaneous ener gy density does not oscillate w ith time at the harmonic fo