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DESY, FLASH and XFEL


XFEL


XFEL versus FLASH


XFEL versus LCLS and SPring8


Two-colour short-pulse photoionization of atoms
Infrared (IR) laser pulse: = 1.66 eV (800 nm), TL = 2.5 fs I = 10
12

­ 10

14

W/cm

2

XUV pulse

= 70 ­ 130 eV

The main parameters: L - duration of the IR pulse XUV - duration of the XUV pulse TL - period of the IR pulse Two limiting cases: A: B: Streaking Sidebands


Case A: , streaking experiment
(Qualitative explanation)
0.04 0.04
Electric field (arb. units) Electric field (arb. units) Electric field (arb. units) Electric field (arb. units)
0.02 0.02 0.02 0.01 00 00

z

Laser field: strong, 1013 -1014 W/cm2,
few-cycle, L~ 5 fs, EL = 1.6 eV (800 nm)

-0.01 -0.01 -0.02 -0.02 -0.02 -0.02 -0.03 -0.04 -0.04 -0.0300 00 100 100 100 200 300 200 300 300 200 300 Time delay (a.u.) Timedelay (a.u.) delay (a.u.) delay (a.u.) Time 400 400 400 500 500 500

XUV pulse: weak, X~300 as, EX=90eV Modification of electron spectra in a strong IR field:

20

10

A(t) (arb. units)

0

-10

a) Energy shift
100 200 300 Time delay (a.u.) 400 500

-20 0

b) Energy spread


Theoretical results: Ar (3s) photoionization
Example:
A.Kazansky and N. Kabachnik J. Phys. B 40, 2163 (2007)

Ar (3s); I= 28.6 eV

IR: L= 5 fs, = 800 nm, W = 1013 W/cm

2

XUV: EX= 90 eV , X = 330 as


Experimental results: Ne(2p) photoionization
Example:
M. Gouliemakis et al. Science 305, 1267, 2004 Pump: XUV, E=93 eV, T=250 as Probe: IR 750 nm, T=5 fs

Photoelectrons are detected along the laser polarization


Case B: , sideband formation
Emitted electron interacts with the laser field: it can absorb or emit IR - photons

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


Theory: strong field approximation
L. Keldysh 1965 Amplitude of photoionization

Electron wave function in the laser field (Volkov wave-function):

where Approximately

Volkov phase


Results of calculations. Case A ­streaking regime
IR: I= 3.5 1012 W/cm
2

TL = 2.5 fs (800 nm) XUV: X = 0.5 fs Ee = 220 eV (8.1 a.u.)


Results of calculations for different X
A.K. Kazansky, I.P. Sazhina, N.M. Kabachnik, Phys.Rev. A 82, 033420, 2010 2 fs 1 fs

3 fs

4 fs


Description of the gross structure

where Suppose for simplicity that

Stationary phase approximation
Result:


Sideband formation in laser-assisted Auger decay
First experiment: J.M. Schins et al. PRL 73, 2180, 1994 LMM transitions in Ar IR laser 800 nm

e

a

e

p

TOF electron spectrometer of the magnetic bottle type 2p 2s

1s

Ne


Sideband structure for Ne KLL Auger transition
A. Kazansky and N. Kabachnik J. Phys. B 43, 035601 (2010) Ne (1s), KLL EA = 804.3 eV (30 a.u.) A = 2.4 fs (100 a.u.)

X-ray: X = 1 fs IR: L = 20 fs


Sidebands at different emission angles

0

o

45

o

60

o

75

o

90

o


Angular dependence of the gross structure

Angle-integrated spectrum


Recent experiment at LCLS
M. Meyer et al 2010 unpublished


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