Two-center resonant photoionization in slow atomic collisions & strong laser fields

Transcription

1 Two-center resonant photoionization in slow atomic collisions & strong laser fields A.B. Voitkiv,1 J. Fedyk,2 S.F. Zhang,3 X. Ma3 and C. Müller1 Institut für Theoretische Physik I, Uni Düsseldorf 2 Physikalisch-Chemisches Institut, Uni Heidelberg 3 Institute of Modern Physics, Lanzhou, China 1 DPG-Frühjahrstagung der Sektion AMOP, Rostock, 14. März 2019

2 Two-center resonant photoionization: Introduction

3 Scheme of the process

4 Scheme of the process

5 Scheme of the process internuclear separation Dipole-dipole coupling:

6 Probability of the process direct channel two-center channel Li-He system = / a Theory by Najjari et al., PRL (2010)

7 Probability of the process direct channel two-center channel Li-He system Relative enhancement: = / a Theory by Najjari et al., PRL (2010) Experiment on He-Ne dimers by Trinter et al., PRL (2013)

8 Two-center resonant photoionization in slow atomic collisions

9 Scheme of the process At target density nb~ cm-3 : mean interatomic distance ~ Å Does the two-center channel become irrelevant?

10 Theoretical description Adiabatic condition: 0 a0 / v 1 { Classical trajectory: 50 ev / u Ecoll 1 kev / u

11 Theoretical description Adiabatic condition: Transition amplitude: Cross section: 0 a0 / v 1 { Classical trajectory: 50 ev / u Ecoll 1 kev / u

12 Theoretical description Adiabatic condition: 0 a0 / v 1 { Classical trajectory: 50 ev / u Ecoll Transition amplitude: Cross section: Relative enhancement: effective distance : 1 kev / u

13 Numerical examples H and He: 0 = 21.2 ev for 1s2 1s2p transition in helium nb ~ 1013 cm-3, target size and photon mean free path ~ 0.1 mm, 1 ( taking bmin = 5 Å ) Li and Mg: 0 = 6.1 ev for 3s2 3s4p transition in magnesium nb ~ 1010 cm-3, target size and photon mean free path ~ 5 mm, 1 ( taking bmin = 5 Å ) H- and Rb: 0 = 1.59 ev for 5s1/2 5p3/2 transition in rubidium nb ~ 1010 cm-3, target size and photon mean free path ~ 1 mm, ~ 103 ( taking bmin = 5 Å ) corresponding experiment planned at IMP, Lanzhou Voitkiv et al., arxiv:

14 Two-center resonant photoionization in strong laser fields

15 Scheme of the process

16 Theoretical description Bichromatic laser field: low frequency 1 high (resonant) freq. 2 Transition amplitude: Volkov state Ionization rate: dressed states

17 Photoionization in a He-Ne system bichromatic 2CPI 1 = 0.85 ev, 2 = ev, I1 ~ 1013 W/cm2, I2 ~ 106 W/cm2, R = 5 Å Fedyk et al., PRA 98, (2018)

18 Photoionization in a He-Ne system bichromatic 2CPI bichromatic 1CPI monochromatic 2CPI single-center PI in A 2 single-center PI in A 1 1 = 0.85 ev, 2 = ev, I1 ~ 1013 W/cm2, I2 ~ 106 W/cm2, R = 5 Å Fedyk et al., PRA 98, (2018)

19 Conclusion Two-center resonant photoionization was generalized to (slow) atomic collisions and relatively strong laser fields. Despite the R -6 scaling, 2CPI can lead to substantial enhancement of ionization also in collisions; experimental verification planned in H- - Rb collisions. Enhanced ionization occurs in bichromatic fields as well; might be tested with He-Ne dimers in weak soft-xuv beam (resonant) + moderately strong near-optical laser field. Thank you for your attention!

20 Semiclassical approximation Applicability conditions: Large incident momentum Pi 1 a.u. Pi Pf (2 E)1/2 with reduced mass and inelasticity E Small scattering angle s 1 In our case: Pi ~ 100 a.u., E 0 due to resonant character of the process s ~ P / Pi 1 with P ~ 1/(bv) ~ 1 a.u since bmin~ 10 a.u. and v ~ 0.1 a.u. See, e.g., McDowell & Colemann, Introduction to the Theory of Ion-Atom Collisions

21 Photoionization in a He-Ne system bichromatic 2CPI monochromatic 2CPI bichromatic 1CPI single-center PI in A 2 single-center PI in A 1 1 = 1.7 ev, 2 = ev, I1 ~ 1012 W/cm2, I2 ~ 1 W/cm2, R = 5 Å Fedyk et al., PRA 98, (2018)