[1] Spielmann C,Burnett N H,Sartania S,et al.Generation of coherent x-rays in the water window using 5-femtosecond laser pulses[J].Science,1997,278:661

[2] Takahashi E,Nabekawa Y,Otsuka T,et al.Generation of highly coherent submicrojoule soft x rays by high-order harmonies[J].Phys.Rev.A,2002,66:021802

[3] Shon N H,Suda A,Midorilawa K.Generation and propagation of attosecond pulses in He gas with sub-10fs driver pulses[J].Phys.Rev.A,1999,60:2578

[4] Hentschel M,Kienberger R,et al.Attosecond metrology[J].Nature,2001,414:509

[5] Hermann M R,Fleck J A.Split-operator spectral method for solving the time-dependent Schrodinger equation in spherical coordinates[J].Phys.Rev.A,1988.38:6000