1. Circular dichroism in laser-assisted short-pulse photoionization of atoms
N. Kabachnik
Institute of Nuclear Physics, Moscow State University
A. Kazansky
Donostia International Physics Center (DIPC)

2. Outline
1. Chirality and circular dichroism in photoabsorption and photoemission.
2. Two-colour XUV+IR experiments. Sidebands in angle
resolved photoelectron spectra.
3. Circular IR dichroism in two-colour multiphoton ionization
with circularly polarized XUV radiation.
4. Circular IR dichroism in two-colour multiphoton ionization
with linearly polarized XUV radiation.

3. photoabsorption and photoemission.
Chirality and circular dichroism in
photoabsorption and photoemission.
(One-photon absorption)

4. Circular dichroism in photoabsorption
Chiral molecule
Circular dichroism
Oriented atoms

5. Circular dichroism in photoemission
(a) Natural chirality e
(b) Chirality, induced by experimental conditions
Circular Dichroism in Angular Distribution

6. Two-colour multiphoton ionization of atoms

7. Two-colour short-pulse photoionization of atoms
Electron spectra in two-colour photoionization
Infrared (IR) laser pulse:
ω= 1.55 eV (800 nm), TL = 2.5 fs
I = 1012 – W/cm2
XUV pulse
ω= 70 – 130 eV
Sideband formation:
Emitted electron interacts with the laser field:
it can absorb or emit IR - photons

8. Experimental results: He photoionization
Example: Glover et al. PRL 76, 2468 (1996)

9. Experimental results from FLASH
M. Meyer et al. JPB 43, 1 (2010)
XUV: 91.8 eV;
XUV: 48.5 eV;
IR: 800 nm; I= 2x1011 W/cm2
IR: 800 nm; I= 4x1013 W/cm2

10. Strong field approximation
L. Keldysh 1965
Amplitude of photoionization
Electron wave function in the laser field (Volkov wave-function):
Volkov phase
where
Approximately

11. Sidebands at different emission angles
A.K. Kazansky et al. PRA 82, (2010) z ϴ e E
IR: 3.5 x 1012 W/cm2
Ee = 220 eV Ne (2p)

12. Recent experiment at LCLS
M. Meyer et al submitted to PRL
Ne KLL Auger transition Ea = 803 eV
IR: ~ 1012 W/cm2

13. with circularly polarized XUV pulse
Circular IR dichroism in two-colour ionization
with circularly polarized XUV pulse

14. Circular dichroism in multiphoton ionization
One-colour ionization
In one-colour multiphoton ionization CD is zero
P. Lambropoulos PRL 29, 453, (1972)
Two-colour ionization
In two-colour multiphoton ionization CD can be non-zero!
N.L. Manakov et al. J. Phys. B 32, 3747 (1999)

15. One-colour multiphoton transition: no CD !
(l=0; m=0)
(p;1)
(d;2)
(f;3)
(g;4)
(p;-1)
(d;-2)
(f;-3)
(g;-4)
Two-colour multiphoton transition: CD can exist!
(p;1)
(d;2)
(f;3)
(g;4)
(s,d;0)
(l=0; m=0)
(p,f;-1)
(d,g;-2)
XUV

16. Results of calculations for He
XUV: E = 90 eV
IR: W = W/cm2
(800 nm, 20 fs)
Both beams are along z-axis
DDCS
Dichroism ϴ e z

17. Spectrum and dichroism at 90 deg.
Angular distributions for the central line

18. Integral spectrum and dichroism

19. Circular IR dichroism in two-colour ionization
with linearly polarized XUV pulse

20. Results of calculations for He
XUV: E = 90 eV
IR: W = W/cm2
(800 nm, 20 fs)
Both beams are along z-axis
Dichroism
DDCS z x y E e φ

21. Spectrum and dichroism at 45 deg.
Angular distributions for the first sideband

22. Conclusions
1. Circular dichroism in two-colour IR+XUV multiphoton ionization of atoms is a notable effect and can be studied experimentally at modern experimental facilities.
2. If both beams are circularly polarized the dichroism can be studied both in angle-resolved and in angle-integrated experiments. If the XUV-beam is linearly polarized the dichroism can be observed in angle-resolved experiments only.
3. A study of circular dichroism provides information on phases of matrix elements involved
4. Measurements of circular dichroism can be used to measure, control and monitor of the circular polarization of XUV and X-rays

23. Acknowledgments
I. Sazhina Institute of Nuclear Physics, Moscow State University
A. Grigorieva Fock Institute of Physics, State University of Saint Petersburg
Michael Meyer European XFEL GmbH, Hamburg
Kiyoshi Ueda Institute of Multidisciplinary Research for Advanced Materials,
Tohoku University, Sendai

24. END