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

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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