Doppler - free spectroscopy and isotopic shift of the Mg I resonance line at 285 nm

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Doppler - free spectroscopy and isotopic shift of the Mg I resonance line at 285 nm

S. Le Boiteux, A. Klein, J.R. Rios Leite, M. Ducloy

To cite this version:

S. Le Boiteux, A. Klein, J.R. Rios Leite, M. Ducloy. Doppler - free spectroscopy and isotopic shift of the Mg I resonance line at 285 nm. Journal de Physique, 1988, 49 (6), pp.885-887.

�10.1051/jphys:01988004906088500�. �jpa-00210775�

885

LE JOURNAL ^DE PHYSIQUE

Short communication

Doppler - ^free spectroscopy ^and isotopic shift of the Mg ^I

^reso-

nance

line

at

285

nm

S. Le Boiteux, ^A. Klein, ^{J.R. Rios}

Leite(*)

^{and M. Ducloy}

Laboratoire de Physique ^des Lasers, ^{U.A. au CNRS} N°282, Université Paris-Nord, Avenue J.B.

Clément, ⁹³⁴³⁰ Villetaneuse, ^France

(Re§u

^{le 11} février 19881 accept£ ^sous forme définitive ^{le 17}

mars 1988)

Résumé.2014 La spectroscopie d’absorption ^{saturée sans} élargissement Doppler de la raie de résonance du Mg ^{I à 285 nm}

(transition 1S0

²⁰¹⁴¹

P1)

^a été réalisée avec une source UV continue monomode, ^{et a} permis ^une nouvelle détermination de la structure isotopique ^{de cette raie.}

Abstract.2014 Doppler-free ^saturated absorption spectroscopy ^{of the} Mg ^{I resonance line at 285 nm}

(1S0 20141

^P1

transition)

^{has been} performed ^{with a c.w.} single-mode ^UV source, and has led to a new

determination of the isotopic ^structure of this line.

Tome 49 N°6 JUIN 1988

J.

Phys.

^{France 49}

(1988)

^{885-887 JUIN}

^1988,

Classification

Physics ^Abstracts

42.50 - 32.80

This letter presents ^the first observa- tion of c.w.

Doppler-free

^saturated

absorption

at 285.2 _nm, on the

Mg

^{I resonance line}

[3S2 ’So - 3s3p’PO]

^{as well as a new measure-}

ment of the

isotopic

^{structure of} this line. Such measurements have been made in the past

by

means of either atomic beam studies

(in absorp-

tion

[1]

^{or emission}

[2] )

^or hollow cathode dis-

charge

^with

Mg

^{as an}

impurity.

^Natural magne-

sium presents ^three

isotopic species 24Mg, 25mg, 26Mg,

^with

respective proportions 78.6 % ,

^10.1

% ^{and 11.2} % . The nuclear

spins

^{of the even}

isotopes

^{is zero but}

25Mg

^{has a nuclear}

spin

I

= 5/2 .

^{The 1}

^Po hyperfines

^{structure of this iso-}

tope has been measured

[3]

^{and the total}

^split-

ting

between the three components is less than 50 MHz. The lifetime of

the 1 Po

^level

^being

^of

2 ns

[4] (which corresponds

^{to a} width of the ^or-

(*)

^{Pecmanent address :} D6partamento ^de Fisica, Universidade federal de Pernambuco, 50000, Recife,

Brazil.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:01988004906088500

886

der of 80

MHz) ,

^the

^hyperfine

^{structure is not}

resolved.

The measurement of these

isotopic

^shifts

presented

^{in this} paper is made

by

^{use of a}

saturated

absorption technique.

These kinds of non-linear

optical techniques require sufficiently powerful beams,

^{and were}

quite

^{difficult to} per- form with c.w. UV beams until the recent devel-

opments ^{of c.w.}

frequency doubling

^and

mixing

[5] . By intracavity

second-harmonic

generation

of a c.w.

ring dye

^laser

radiation,

^{we have been}

able to obtain powers up to ^a few milliwatts at 285 nm. For

this,

^{we use a} stabilized

single-

mode

ring dye

^laser

[6] , ^{pumped by}

^{an argon}

ion laser at 514.5 nm

(pump

^{power -- 8}

Watts).

The fundamental beam at 570 nm is obtained with Rhodamine 6G. We put ^{a KDP}

crystal

^cut

at Brewster

angles

^{inside the} collimated arm of the

ring cavity.

The second harmonic _genera- tion is obtained

by angle-matching (type

^{I dou-}

bling).

^{The UV output} beam is extracted

by

transmission

through

^{one of the}

cavity

^mirrors.

It is

horizontally polarized,

and tunable over 60 GHz and like the fundamental

beam,

^{it is}

single- mode, frequency-stabilized (frequency ^jitter

²

MHz).

^The

^typical

^{UV output is 5 mW.}

We use the

ordinary

^saturated

absorption ring configuration

^{with two beams counter-}

propagating

^{in the}

Mg

^oven cell. The

saturating

beam is modulated at 1 kHz and we detect the modulation induced on the

counter-propagating probe

beam. The

Mg

^oven is heaten at 550 K

typically,

^which

corresponds

^{to 5.5 X}

^101°

^atoms

per cm3. The beam

absorption

^{is about 80}

% ,

on line center.

Figure

¹ presents the saturated

absorp-

tion spectrum recorded in these conditions. ^As

shown,

^{the three}

isotopic

^{resonance lines are well}

separated,

^{but the}

hyperfine

^{structure of the}

25Mg

^line

(central resonance)

^{is not resolved.}

Table I presents the different

isotopic

^shifts

given by

^several

authors,

ⁱⁿ

comparison

^with

our measurements

(1 ).

^{There is a bad agreement}

(1)

^{As we do not know the} intensities of the dif- ferment hyperfine ^component intensities, ^{we have}

determined the

25Mg

^{resonance center} by ^con- sidering ^the lineshape ^{as a} Lorentzian one. This

approximation ^may bring ^a slight ^{error on the}

exact determination of the center of gravity ^of

this line.

between the different results but -we stay ^inside the variation of the

previous

^{ones. The last line}

gives

the theoretical

prediction

^{of Vinti}

[7] .

^Let

us remind that there are two main contributions

to the

isotopic

^{shifts : a mass effect and a vol-}

ume effect. Mass effects come from the fact that the center of mass does not coincide with the nucleus and moves with the electrons : Bohr effect

(or

^normal

shift)

^and

^specific

^{shift are}

the two mass effects. The normal shift is well- known but the

specific

^shift

requires

^{the knowl-}

edge

of atomic radial functions. The volume ef- fect comes from the difference between the _po- tentials inside the

nucleus,

^{from one}

isotope

^to

the other. In his

theory,

^Vinti

neglects

^{the vol-}

ume effect on one

hand,

^{and on} the other hand makes an

explicit

calculation of the radial func-

tions,

for different resonances lines with some

approximations (in particular,

^he supposes that the radial function for the orbital 3s of the

3s3p configuration

^is

equal

^{to the orbital}

(3s’)

^{of 3s}

2S(Mg II)).

^The

discrepancy

^{between our} exper- imental result and Vinti’s result could

originate

in the

approximations

made for the calculation of the mass shift. That the volume effect is _neg-

ligible,

is indeed confirmed

by

^the

experimental

value that we have obtained for the

isotopic

^shift

ratio :

8v26,24 /825,24 ==

^1.93

[4] . By comparison

the

prediction

^{for a} pure ^mass shift is

straight- (M26-M24)M25

forwardly

given

by (M25-M24)M26 =

^1.923.

Fig. ^{1.- Saturated}

absorption

spectrum ^{of the} Mg ^{I resonance line}

iso

^-1

po (285.2 nm). (a), (b)

^and

(c)

^{are the} respective isotopic ^lines

24 Mg, 25Mg, 26 Mg.

^{The lower trace} gives ^the

transmission fringes ^{of a confocal} Fabry-Perot resonator, ^{at the} fundamental wavelenght, ⁵⁷⁰

nm

(free

^spectral range -- 83

MHz).

Note that we have measured saturated ab-

sorption

linewidths

(FWHM)

^for the three iso-

topes, of the order of 100

MHz,

^{close to the the-}

oretically predicted

fluorescence linewidths.

887

Table 1.-

Isotopic shifts of

^the

Mg

^{I resonance dine}

(IS,

^-1

^PO;

^{A = 285.2}

nm).

The

respective

^resonance

heights

^{are for}

24Mg

^to

26Mg,

⁷⁰

%, 12

% ^{and 18} % .

They

^are

slightly

^{different from the}

isotopic

^abundance

of natural

Mg.

^The

discrepancy

^is

probably

due to the

overlapping

^{of the}

Doppler-broadened absorption

lines of the three

isotopic species

(FWHM Doppler

^{width -- 2.5}

GHz).

^{Due to}

this

frequency-dependent absorption,

^{the laser}

beam

intensity

differs from one resonance cen-

ter to another.

In

conclusion,

^{we have}

presented

^a new,

Doppler-free,

measurement of the

isotopic

^shifts

of the 285.2 nm

Mg

^{resonance line. In}

spite

^of

the low available UV _power, we have been able to monitor

Mg

^saturated

absorption

resonances.

By combining

^{this source with}

high-frequency heterodyne

spectroscopy

techniques [10] ,

^one

should be able to

seriously improve

^the

signal sensitivity

and monitor weaker UV lines. We

plan

^{to use this UV source to}

perform

^three-

level

[11] , cascade-up,

saturation spectroscopy and

high-order

^wave

mixing [12] ,

ⁱⁿ

Mg

vapor.

Aknowledgement.

The authors wish to thank Cid B. de

Araujo

for his

help

^{in the}

preliminary

steps ^{of this ex-}

periment.

References

[1] ^JACKSON, D.A., KUHN, H.,

Proc. R. Soc.

A 154

(1936)

^679.

[2] ^{FISHER, R.A.,}

^{Rev. Mod.}

^Phys.

¹⁴

(1942)

79.

[3] JURGEN-KLUGE,

^HATTO

SAUTER,

^Z.

Phys.

270

(1974)

^295.

[4]

^{ZHUVIKIN, G.V., PENKIN,}

^N.P.,

SHABANOVA,

L.N., Opt. Spect.

⁴¹

(1976)

5.

[5]

COUILLAUD,

B.,

DUCASSE, ^{A. Rev. du}

Cethedec,

^{ondes et}

signal,

^NS 82, p. 33, ^and references therein.

[6]

Commercial type ^{CR 699.21}

(Coherent).

[7] VINTI, J.P., Phys.

^{Rev. 56}

(1939).

[8] KELLY, F.M.,

^{Can. J.}

Phys.

³⁵

(1957)

1222.

[9] MURAKAWA,

^J.

Phys.

^Soc.

Jpn

⁸

(1953)

213.

[10] RAJ, R.K., BLOCH, D., SNYDER, J.J., CAMY,

^{G. and}

DUCLOY, M., Phys.

^Rev.

Lett. 44

(1980)

^1251.

[11]

^LE

BOITEUX, S., BLOCH, D., DUCLOY, M., PESNELLE, A., RUNGE, S.,

^and

PERDRIX, M., Opt.

^{Commun. 52}

(1984)

^274.

[12] TABOSA, J.W.R.,

^LE

BOITEUX, S.,

SIMONEAU, P., BLOCH,

^{D. and}

DUCLOY,

M., Europhys.

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