Light induced atomic desorption [LIAD ] and related phenomenacewqo08.phy.bg.ac.rs/UserFiles/File/prezentations/Moi.pdf · Light induced atomic desorption [LIAD ] and related phenomena

Light induced atomicdesorption [LIAD] and

related phenomena

atomsphotons

L. Moi

Physics Dept Siena University - CNISM

CEWQO 2008

We are interested to processes involving

atoms+surface+light

Alkali atomsCoated glassPorous silica

Weak Coherent-incoherent

cell

Laser beam

We study this effect, welook at the modificationsintroduced by LIAD on thewhole system and at possibleapplications

LIAD

New momentum grew up because of new experiments made with ultra-thincells and nano structured materials, because of miniaturization of manyapparatus (traps, atom chips etc.) and the discovery of new phenomena.

It is well known that Light hitting a surface triggers many differentprocesses depending on its intensity, frequency, pulsed or c.w. regime. Highintensity produces ionization, plasma formation, ablation etc.

In the past atom-surface interaction [no light!] was a crucial problem

In optical pumping atom-wall collisions destroy spin orientation

In light induced drift atoms adsorbed at the surface make drift velocity very slow

surface density in fact grows up with the adsorption energySolution --> walls coating with organic film

+ light !

+Low intensity

Weak light triggers other interesting effects with alkali atoms in coatedcell and nanoporous silica.

LIAD

light atoms

PDMS

OCT

Paraffin GlassSapphire

Stainless steel

Porous glass

+dry film

PDMS OCT

!

E " 0.1eV

PDMS

Few isolated atoms at the surface

Desorbing light is the resonant laser itself et al., Nuovo Cimento D15, 709, 1993 A.Gozzini

Room temperature!!

LIAD Effect

l. Moi :”Gas manipulation by

light”; Frontiers in laser

spectroscopy (1994) North

Holland - T.Hansch and M.

Inguscio Eds. Pg. 167

IL < 1 mW/cm2

Pocket lamp

!

"max

=nmax

# n0

n0

$ IL

R =1

n0

dn

dt

%

& '

(

) * t= t

0

= kIL

Taking into account both desorption fromsurface and diffusion inside the film, twoparameters characterize the LIAD effect:

filmsurface

vapor

C. Marinelli et al. Eur. Phys. J. D13 (2001) 231

C. Marinelli et al. Eur/ Phys. J. D 37 (2006) 319

S.N.Atutov et al. PRA 60 (1999) 4693

Similar one dimension model has been proposed by Budker et al. for paraffin. PRA 66

(2002) 042903 with essentially the same results.

0 200 400 600 800

0

1

2

3

4

t2

t1

t0

!LIAD

t(s)

0

2

4

6

8

10

0 5 10 15 20

Ab

sorp

tio

n s

ign

al(n

orm

aliz

ed t

o e

qu

ilib

riu

m v

alu

e)

t(s)

(a)

!

!

t0

t1

"t

Surface + bulk effectLight modifies the atom diffusioninside the coating.The coating becomes an atomicreservoir.

Budker et al. PRA 66 (2002) 042903

“ there are several proposals to explain the dependence of LIAD on the

frequency of the desorbing light. Bonch-Bruevich et al. suggest that the

frequency dependence is related to the absorption spectrum of adsorbed

atoms. Another idea is that the alkali-metal atoms form quasimolecular

bonds with the coating and the photon energy must exceed some threshold.

It is still difficult to distinguish between these various possibilities with our

present data”.

pulsed excitation --> high T -

“cw” weak illumination --> diffusion - no dependence on atom

Different regimes different mechanisms -

PDMS film quite complex system and diffusion goes on in the dark!

At different temperature

C. Marinelli et al., Eur.Phys.J. D 37 (2006)

is the same for Rb and Cs

C. Marinelli et al., Eur.Phys.J. D 37 (2006)

Optical absorption spectrum of aPDMS sample with a thickness of1cm.

Light off

Light on

107 atoms in 2sRb source at room temperature

8 106 atoms in 40msRb source @T<0°C

!

E "1eV

Pore size 5-20 nm

Porous silica

We use as host matrix for atoms and nanoparticles porous silicawith a mean pore diameter of 17 nm and a free volume of about50% of the whole silica mass.

~17nm

Pore volume: 500mm3/gPore surface: 100m2/gMean pore diameter: 17nmSi02>96%

REM picture - VitraBio

The porous glass sample is a rectangular plate 30x15x1mm3 in size.It is placed inside a Pyrex resonance cell, kept at roomtemperature, and filled with rubidium or cesium.

The sample is fixedclose to one of thecell windows by aPyrex Ring sealed tothe cell body

0.4g=40m2

Rb/Csmetal

Phys. Rev.Lett. 97 157404 (2006)

Optics Express 16, 1377 (2008)

The desorbing rate R and the maximum increase of thevapour density !max are measured as function of the

desorbing light intensity and frequency.

0

0max

0

maxmax

n

nn

n

n !=

"=#

00

1

=

=t

dt

dn

nR

Argon+@514nm

Argon+@514nm

Photodesorption Photodesorption dependence on light intensitydependence on light intensity

A. Burchianti et al. Physical Review Letters 97 (2006)

NIR illumination

Green illumination

15mW/cm2@514nm

27mW/cm2@810nm

Photodesorption dynamics

NIR-BLUE-NIR sequence of colours

Double NIRillumination

488nm 5.6mW/cm2

illuminated area 0.3 cm2

808nm 2W/cm2

illuminated area 0.1 cm2

Six shots

By alternately illuminating the sample with blue-green and NIR light we find

that the PG sample remembers the illumination sequence!

Sequence light pulses: red+green+red+2green+red

Burchianti Burchianti et et al., al., PRL PRL 97 97 157404 (2006)157404 (2006)20mW@532nm/ 50mm2

260mW@810nm/16mm2

In the dark the system relaxes to the equilibrium conditionIn the dark the system relaxes to the equilibrium condition

Storing and erasing images in Storing and erasing images in Rb Rb loaded PGloaded PG

2.5W/cm2 at 1.5eV; 30s

Optics Express 16, 1377 (2008)

20mW/cm2 at 2.3eV; 2min

Cluster growth induced by UV-visible light

is correlated to LIAD

NIR light induce both cluster evaporation via SPID andcluster growth via LIAD

The photon energy dependence of Surface Plasmon InducedDesorption is dominated by dipolar surface plasmon frequency. For aspherical metal particle we get

Change of PG Absorbance Cluster Formation

PG 17nm with Rb PG 17nm with Cs

band (1) band (2)

we apply Gans theory that describes the opticalproperties of randomly oriented spheroids withsize R << "

( )( )( )

( ) ( )

( )

1

)1(2

1

tan1

1

/1

3

2

2

1

3

2

2

1

2

2

2

22/3

!=

!"==

!"+

=

#$%

&'( !

++

"""=

!

)

c

ae

PPP

eee

eP

P

P

PV

c

cba

c

i

i

i

m

i

mext

*+*+*

+**

++,

for oblateparticles (c<a=b)

Rb/PG

(1,1)(1,0)

R=3nm; c/a=0.8R=3nm; c/a=0.8

Light controlled atomic dispensers - fast and clean

Atom delivery in nanostructures -control of optical thicknes with light

Control of cluster formation in nanostructured materials

High vapor densities at room or lower temperatures

References:

[1] A. Burchianti et al., Eur. Phys. Letters 67 (2004) 983

[2] T. Kawalec et al., Chem. Phys. Lett. 420, (2006) 291

[3] A. Burchianti et al., Phys. Rev.Lett. 97 (2006) 157404

[4] L. Moi et al., Proceedings of SPIE, Volume 6604 (2007)

[5] A. Burchianti et al., Optics Express 16, 1377 (2008)

[6] A.Burchianti et al., submitted to EPJ D (2008)

A. Burchianti, A. Bogi, C. Marinelli, E. MariottiCNISM and Physics Department, University of Siena, I-53100 Siena, Italy

C. MaibohmMads Clausen Institute, University of Southern Denmark, DK-6400 Sonderborg, Denmark

S.SanguinettiPhysics Department, University of Pisa, I-56127 Pisa, Italy

S.N. Atutov, K. NasyrovNovosibirsk

A. Bogi, C. Marinelli, A. Burchianti, F. Della Valle,

E.Mariotti, S. Veronesi, G. Bevilacqua,

J. Brewer