[1] Hentschel M, Kienberger R, SpielmannCh, et al. Attosecond metrology[J]. Nature, 2001, 414: 509-513.

[2] Lan P F, Lu P X, Cao W, et al. Attosecond ionization gating for isolated attosecond electron wave packet and broadband attosecondxuv pulses[J]. Phys. Rev. A, 2007, 7(5): 051801.

[3] Popmintchev T, Chen M C, Popmintchev D, et al. Bright coherent ultrahigh harmonics in the keV X-ray regime from mid-infrared femtosecond lasers[J]. Science, 2012, 33(6086): 1287-1291.

[4] Corkum P B. Plasma perspective on strong field multiphoton ionization[J]. Phys. Rev. Lett., 1993, 71(13): 1994-1997.

[5] Lewenstein M, Balcou P, Ivanov M Y, et al. Theory of high-harmonic generation by low-frequency laser fields[J]. Phys. Rev. A, 1994, 49(3): 2117-2132.

[6] Tong X M, Chu S I. Theoretical study of multiple high-order harmonic generation by intense ultrashort pulsed laser fields: A new generalized pseudospectral time-dependent method[J]. Chem. Phys., 1997, 217(2): 119-130.

[7] Miloevi D B, Becker W, Kopold R. Generation of circularly polarized high-order harmonics by two-color coplanar field mixing[J]. Phys. Rev. A, 2000, 61(6): 063403.

[8] Krause J L, Schafer K J, et al. Calculation of photoemission from atoms subject to intense laser fields[J]. Phys. Rev. A, 1992, 45(7): 4998-5010 .

[9] Ivanov I A, Kheifets A S. High harmonics generation from excited states of atomic lithium[J]. J. Phys. B: At. Mol. Opt. Phys., 2008, 41(11): 115603.

[10] Chu X, Chu S I, Laughlin C. Spectral and temporal structures of high-order harmonic generation of Na in intense mid-ir laser fields[J]. Phys. Rev. A, 2001, 64(1): 013406.

[11] Javanainen J, Eberly J H, Su Q C. Numerical simulations of multiphoton ionization and above-threshold electron spectra[J]. Phys. Rev. A, 1988, 38(7): 3430-3446.

[12] Tong X M, Chu S I. Time-dependent density-functional theory for strong-field multiphoton processes: Application to the study of the role of dynamical electron correlation in multiple high-order harmonic generation[J]. Phys. Rev. A, 1998, 57(1): 452-461.

[13] Tong X M, Chu S I. Time-dependent density-functional theory with optimized effective potential and self-interaction correction: Application to the study of coherent control of multiple high-order harmonic generation of He atoms in Mixed Laser fields[J]. Int. J. Quant. Chem., 1998, 69(3): 293-303.

[14] BuendíaE, Gálvez F J, et al. Numerical-parameterized optimized effective potential for atoms[J]. J. Phys. B: At. Mol. Opt. Phys., 2006, 39(17): 3575-3585.

[15] Gálvez F J, Buendía E, Maldonado P, et al. Optimized effective potential energies and ionization potentials for the atoms Li to Ra[J]. Eur. Phys. J. D, 2008, 50(3): 229-235.

[16] Li P C, Sheu Y L, Laughlin C, et al. Dynamical origin of near and below-threshold harmonic generation of Cs in an intense mid-infrared laser field[J]. Nat. Commun., 2015, 6: 7178.

[17] Hu S X, et al. High-order harmonic generation from intense laser-driven inner electrons of Rydberg atoms[J]. Phys. Rev. A, 2004, 69(3): 033405.

[18] Bleda E A, Yavuz I, Altun Z, et al. High-order-harmonic generation from Rydberg states at fixed Keldysh parameter[J]. Phys. Rev. A, 2013, 88(4): 043417.

[19] Du H C, Xue S, Wang H Q, et al. Wavelength scaling of high-order harmonic yield from a Rydberg atom in a few-cycle pulse[J]. J. Opt. Soc. Am. B, 2014, 31(7): 1621-1626.

[20] Mohebbi M. Controlling the ionization and recombination rates of an electron in preexcited ions to generate an intense isolated sub-4-as pulse in a multicycle regime[J]. Phys. Rev. A, 2015, 91(2): 023835.

[21] Zhai Z, Zhu Q R, Chen J, et al. High-order harmonic generation with Rydberg atoms by using an intense few-cycle pulse[J]. Phys. Rev. A, 2011, 83(4): 043409.

[22] Chen J G, Wang R Q, Zhai Z, et al. Frequency-selected enhancement of high-order-harmonic generation by interference of degenerate Rydberg states in a few-cycle laser pulse[J]. Phys. Rev. A, 2012, 8(3): 033417.

[23] Wang Z, He L X, et al. High-order harmonic generation from Rydberg atoms in inhomogeneous fields[J]. Opt. Expr., 2014, 22(21): 25909-25922.

[25] Ralchenko Y. NIST: Atomic spectra database[OL]. http://www.nist.gov/pml/data/asd.cfm.