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Recent Physics and Future Developments. P.A. Hatherly J.J. Thomson Physical Laboratory University of Reading Whiteknights Reading RG6 6AF. Sources used by the Reading Group. I Like SR. Major International Facilities SRS, Daresbury, UK Beamline MPW6.1 PHOENIX MAX II, Lund, Sweden - PowerPoint PPT Presentation
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Recent Physics and Future Developments
P.A. Hatherly
J.J. Thomson Physical Laboratory
University of Reading
Whiteknights
Reading RG6 6AF
Sources used by the Reading Group
• Major International Facilities– SRS, Daresbury, UK
• Beamline MPW6.1 PHOENIX
– MAX II, Lund, Sweden• Beamline I411
• In-house helium lamp– 20 and 40 eV photons– Other energies available using Ne, Ar, Kr, Xe
I Like SR
Physics Programmes
• Inner shell ionisation and excitation of molecules– Carried out at DL and MAX– High Resolution Studies of OCS at S 2p and C 1s
• Absolute Cross Section Measurements– Recent Final Year Undergraduate Project
• Measurement of the absolute absorption cross-section of SF5CF3
• Resolving a conflict in values in the literature
– Future plans to measure cross sections to allow SR data to be placed on an absolute scale
OCS Threshold Electron Studies
• At the SRS, Daresbury– S 2p and C 1s excitation of OCS– Threshold electron and ion yield spectra– Fragmentation studies
• Coincidence studies between threshold electrons and ions
OCS – S 2p Excitations
168 170 172 174
50
100
150
200
250
300
350
S 2p1/2
S 2p3/2
Figure 1. OCS S 2p Ionisation Threshold Photoelectron and Total Ion Yield Spectra
TP
E C
ou
nts
Photon Energy (eV)
168 170 172 1740
20000
40000
60000
80000
100000
TPE
TIY
TIY
Co
un
ts
5000 6000 7000 8000 9000 10000 11000 12000
0.00
0.01
0.02
0.03
0.04
0.05
0.09
0.10
0.11
0.12
0.13
0.14
0.15
I (ar
b.u)
no
rmal
ised
to to
tal r
eal c
oinc
iden
ces
TOF (ns)
1DL6139OCS01 - S 2p1/2 edge 2 DL6139OCS02 - S 2p1/2 -> 4s 3 DL6139OCS03 - S 2p3/2 -> 4s 4 DL6139OCS04 - S 2p3/2 -> 3d 5 DL6139OCS05 - S 2p3/2 -> 5s
C+
CO+f CO+
bS+f
S+b
OCS2+
O+
OCS – S 2p Fragments
OCS – C 1s Excitation
286 288 290 292 294 296 2980
100
200
300
400
500
600
26002800300032003400
OCS C 1s Region Threshold Photoelectron and Total Ion Yield Spectra
TP
ES
Co
un
ts
Photon Energy (eV)
TPES
286 288 290 292 294 296 298
200000
300000
400000
1600000
1800000
2000000
2200000
TIY
TIY
Co
un
ts
OCS – Post C 1s Excitation4p
5p
C 1
s(-1
)
shake
-up
shake
-up
sigm
a(*
)
shake
-up
sigm
a(*
)
shake
-up
294 296 298 300 302 304 306 308 310 312 314 316 318 3201000
2000
3000
4000
5000
TP
ES
Co
un
ts
Photon Energy (eV)
294 296 298 300 302 304 306 308 310 312 314 316 318 3201000000
1200000
1400000
1600000
1800000
2000000
2200000
2400000Assignments from Sham et al (PRA 40 (1989) 652)
TIY
Co
un
ts
OCS – C 1s Fragments
4000 6000 8000 10000 12000
0
200
400
600
800
C 1s->5p (294.2eV) C 1s->thr (295.4eV) C 1s->Pi* (288.36eV) C 1s->1st shakeup (298.2eV)
OCS TPEPICOs
Coin
cidence
Counts
TOF (ns)
C+
CO+f
CO+b
S+f
S+b
OCS2+
O+
OCS Auger Studies
• At MAX II, Sweden– S 2p excitation and Auger spectra– Fragmentation associated with given Auger
channels• Coincidence studies between Auger electrons
and ions
OCS – S 2p Auger Spectrum
120 125 130 135 140 145
0
100
200
300
400
500
600
700
800
S IV S III S II S I
PES - Normal Auger Decay.(Exc. energy 200eV)
Co
un
ts
Kinetic Energy (eV)
OCS – S 2p Fragments
0 1000 2000 3000 4000 5000 60000
50
100
150
Exc. Energy 200eV
Co
un
ts
TOF (ns)
CEI20
0
50
100
150
200
250
300
350
400
CEI19
OCS2+
OCS2+S+
S I
S II
Absorption Cross Sections
• Absorption Cross Section of SF5CF3 measured– Disagreement of a factor of 2 between recently
reported values at 10.2 eV (H Lyman )– Final Year Undergraduate Project
• Andrew Flaxman
– Measured at He I (21.2 eV) and Ne I (16.7 eV, doublet)
Cross Section of SF5CF3
He INe I
5 10 15 20 25 30
0.0
2.0x10-17
4.0x10-17
6.0x10-17
8.0x10-17
1.0x10-16
1.2x10-16
1.4x10-16
H Ly
Ab
sorp
tion
Cro
ss S
ect
ion
(cm2 )
Photon Energy (eV)
From Chim et al (Chem Phys Letts 367 (2003) 697 Present Data
Future Developments
• Recent EPSRC grants to develop attosecond laser technology– Consortium including Reading (Leszek
Frasinski), Oxford, Imperial College and Rutherford
– Why talk about this at a SR meeting?
Attosecond Pulses
• Aim of project to generate pulses of the order of 100 as long– Cannot be “optical” wavelengths
(period ~ 2 fs)– Need VUV/SXR (eg, ~20 eV, period ~ 200 as)– Hence, need SR optics technology to handle
the pulses
Attosecond Pulses
• How to measure the pulse length?– With fs pulses, can use frequency doubling
and autocorrelation techniques– With as pulses, need new techniques
An Application of PES!
Electron Energy
Two delayed as x-ray pulse replicas incident on a gas target…
…each generate an identical photoelectron spectrum
An Application of PES!
Electron Energy
Now add slower, fs, pulse…
…result – interference fringes in the PE spectrum…
…photoelectrons due to each as pulse shifted in energy…
…Details of fringes gives as pulse spectrum and phase information – hence can reconstruct the pulse!
(Quéré et al, PRL 90, 7 (21st Feb 2003))
…energy levels shifted with time…
Attosecond Lasers
• Excellent examples of spin-off technology– VUV and SXR optics well understood in SR
• Now being applied in a new area
– PES developed as a tool for probing fundamental atomic and molecular properties
• Now applied as a tool in it’s own right for a specific technological application
– Note this under “Beneficiaries” etc. on your next EPSRC application!
Other Developments
• Strong possibility of developing a fs laser laboratory at Reading– SRIF funding– High-harmonic generation systems for fs
scale time resolved VUV work
• Ongoing progress of 4GLS– Exciting possibilities of non-linear VUV
phenomena
With Thanks:
• Dr Marek Stankiewicz and Dr Jaume Rius i Riu– SR experiments at Daresbury and MAXlab
• Mr Andy Flaxman– Undergraduate Project Student – Cross
section data
• Dr Leszek Frasinski– Atto- and femtosecond laser development