Programme

P.5 -- Poster, VCTP-49

Date: Wednesday, 31 July 2024

Time: 08:30 - 10:00

Multielectron and multiorbital effects in in odd-even harmonic generation from CO molecules

T. Tran (1), K.-N. H. Nguyen (2), Đ.-A. Trieu (1), Duong D. Hoang-Trong (1), N.-L. Phan (1)

(1) Ho Chi Minh City University of Education, 280 An Duong Vuong Street, Ward 4, District 5, Ho Chi Minh City 72711, Vietnam (2) Institute of Fundamental and Applied Sciences, Duy Tan University, Ho Chi Minh City 71008, Vietnam

Implementing intense laser with an ultra-short pulse duration deepens our understanding of laser-molecule interactions and nonlinear effects. Among the non-linear effects, high-order harmonic generation (HHG) has become a powerful tool in extracting molecules' structures [1], probing molecular dynamics [2,3], and producing attosecond pulse trains or isolated attosecond pulse [4,5]. For a long time, it is popularly acceptable that the highest occupied molecular orbital (HOMO) dominantly contributes to HHG compared to lower-lying orbitals [6,7]. As a result, the single-active electron (SAE) model is usually applied to simulate the HHG emitted from atoms molecules [7,8]. However, recently, it is shown that multielectron effect impacts the HHG spectra of specific atoms and molecules [9,10]. We also demonstrated that multielectron effect described via dynamic core-electron polarization (DCeP) strongly affect the odd-even HHG from CO molecule [11,12]. Moreover, only even-to-odd ratio is reduced by one order of magnitude, making it agrees with experimental data [13,14]. However, since DCeP is the coupling of the laser-induced polarization of the core electron with the active electron, it is the average effect of the core electron. It is still desirable to identify which lower-lying orbitals contribute to odd-even HHG spectra from CO molecule? In this work, we study the multielectron and multiorbital effects on the HHG of CO. The HHG spectrum is calculated using time-dependent density functional theory (TDDFT) embedded in OCTOPUS source code. The obtained spectra are validated by those solving the time dependent Schrödinger equation considering DCeP effect. The results show that the lower-lying orbitals strongly contribute into HHG spectra. More specifically, when the angles between the laser electric polarization and molecular axis (called orientation angle) are larger than 600, both HOMO and HOMO-1 contribute in HHG. In particular, HOMO dominates in low-order HHG while HOMO-1 governs HHG orders after cutoff. More interesting, we find out that for harmonics just before and at cutoff, HOMO contribute to odd harmonic while HOMO-1 to even ones. The time-frequency analysis is proceeded to explain the observed results. [1] M. Lein, N. Hay, R. Velotta, J. P. Marangos, and P. L. Knight, “Interference effects in high-order harmonic generation with molecules,” Phys. Rev A. 66, 1 (2002). [2] J. Itatani, J. Levesque, D. Zeidler, H. Niikura, H. Pépin, J. C. Kieffer, P. B. Corkum, and D. N. Villeneuve, “Tomographic imaging of molecular orbitals,” Nature 432, 867 (2004). [3] M. Lein, “Molecular imaging using recolliding electrons,” J. Phys. B 40, R135 (2007). [4] F. Krausz and M. Ivanov, “Attosecond physics,” Rev. Mod. Phys. 81, 163 (2009). [5] F. Calegari, G. Sansone, S. Stagira, C. Vozzi and M. Nisoli, “Advances in attosecond science,” J. Phys. B: At. Mol. Opt. 49, 062001 (2016). [6] J. Itatani, J. Levesque, D. Zeidler, H. Niikura, H. Pépin, J.-C. Kieffer, P. B. Corkum and D. M. Villeneuve, “Tomographic imaging of molecular orbitals,” Nature 432, 867 (2004). [7] M. Peters, T. T. Nguyen-Dang, E. Charron, A. Keller and O. Atabek, “Laser-induced electron diffraction: a tool for molecular orbital imaging,” Phys. Rev. A 85, 053417 (2012). [8] X. Zhu, X. Liu, Y. Li, M. Qin, Q. Zhang, P. Lan and P. Lu, “Molecular high-order-harmonic generation due to the recollision mechanism by a circularly polarized laser pulse,” Phys. Rev. A 91, 043418 (2015). [9] B. K. McFarland, J. P. Farrell, P. H. Bucksbaum and M. Guhr, “High Harmonic Generation from Multiple Orbitals in N2,” Science 322, 1232 (2008). [10] W. Li, X. Zhou, R. Lock, S. Patchkovskii, A. Stolow, H. C. Kapteyn and M. M. Murnane, “Time-Resolved Dynamics in N2O4 Probed Using High Harmonic Generation,” Science 322, 1207 (2008). [11] T. H. Nguyen, K.-N. H. Nguyen, N.-L. Phan, C.-T. Le, D. Vu, L.-P. Tran, and V.-H. Le, “Imprints of multielectron polarization effects in odd-even harmonic generation from CO molecules,” Phys. Rev. A 105, 023106 (2022). [12] K.-N. H. Nguyen, , N.-L. Phan, C.-T. Le, D. Vu, and V.-H. Le, “Parameter-free retrieval of subcycle asymmetry of polar molecules by high-order harmonic spectroscopy,” Phys. Rev. A 106, 063108 (2022). [13] E. Frumker, N. Kajumba, J. B. Bertrand, H. J. Wörner, C. T. Hebeisen, P. Hockett, M. Spanner, S. Patchkovskii, G. G. Paulus, D. M. Villeneuve, A. Naumov, and P. B. Corkum, “Probing Polar Molecules with High Harmonic Spectroscopy,” Phys. Rev. Lett. 109, 233904 (2012). [14] P. M. Kraus, D. Baykusheva, and H. J. Wörner, “Two-Pulse Field-Free Orientation Reveals Anisotropy of Molecular Shape Resonance,” Phys. Rev. Lett. 113, 023001 (2014).

Presenter: Trần Thành