Exploration of Below-Threshold Harmonic Generation Mechanisms of Cesium Atoms in Intense Mid-Infrared Laser Pulses
We present a non-perturbative quantum study of high-order harmonic generation (HHG) of Cesium atoms in intense mid-infrared laser pulses. An accurate angular-momentum—dependent model potential is constructed for the high-precision description of the Cs atom electronic structure. The three-dimensional time-dependent Schrodinger equation is solved accurately and efficiently by means of the time-dependent generalized pseudospectral methods (TDGPS) [Tong and Chu, Chem Phys 217(2–3), 119–130 (1997)].Besides the expected odd harmonics, the calculated HHG power spectra show additional structures due to the strong 6s–np couplings. The spectral and temporal characteristics of the HHG are further explored through the wavelet transformation [Tong and Chu, Phys Rev A 6102(2), 21802 (2000)]. As a result, we can investigate the prevailing mechanisms in different energy regimes, especially those contributing to the below- and near-threshold harmonics [Power et al., Nat Photon 4(6), 352–356 (2010); Soifer et al., Phys. Rev. Lett. 105(14), 143904 (2010); Yost et al., Nat Phys 5(11), 815–820 (2009)].
KeywordsTime Profile Wavelet Transformation Group Delay Energy Regime Cesium Atom
This work was partially supported by the U.S. Department of Energy and by the U.S. National Science Foundation. We also would like to acknowledge the partial support of National Science Council of Taiwan (Grant No. 100-2119-M-002-013-MY3) and National Taiwan University (Grant No. 10R80700).
- 1.A. Lhuillier, K.J. Schafer, K.C. Kulander, Theoretical aspects of intense field harmonic-generation. J. Phys. B Atom. Mol. Opt. Phys. 24(15), 3315–3341 (1991)Google Scholar
- 2.P.B. Corkum, Plasma perspective on strong field multiphoton ionization. Phys. Rev. Lett. 71(13), 1994 (1993)Google Scholar
- 3.E.P. Power et al., XFROG phase measurement of threshold harmonics in a Keldysh-scaled system. Nat. Photon. 4(6), 352–356 (2010)Google Scholar
- 4.H. Soifer et al., Near-threshold high-order harmonic spectroscopy with aligned molecules. Phys. Rev. Lett. 105(14), 143904 (2010)Google Scholar
- 5.D.C. Yost et al., Vacuum-ultraviolet frequency combs from below-threshold harmonics. Nat. Phys. 5(11), 815–820 (2009)Google Scholar
- 6.Y.J. Chen, S.I. Chu, C. Laughlin, in preparationGoogle Scholar
- 7.J.E. Sansonetti, Wavelengths, transition probabilities, and energy levels for the spectra of cesium (Cs I–Cs LV). J. Phys. Chem. Ref. Data 38(4), 761–923 (2009)Google Scholar
- 8.X.M. Tong, S.I. Chu, Theoretical study of multiple high-order harmonic generation by intense ultrashort pulsed laser fields: a new generalized pseudospectral time-dependent method. Chem. Phys. 217(2–3), 119–130 (1997)Google Scholar
- 9.X.M. Tong, S.I. Chu, Probing the spectral and temporal structures of high-order harmonic generation in intense laser pulses. Phys. Rev. A 6102(2), 21802 (2000)Google Scholar
- 10.L.V. Keldysh, Ionization in field of a strong electromagnetic wave. Sov. Phys. JETP USSR 20(5), 1307 (1965)Google Scholar