THERMAL AND STIMULATED MOLECULAR SCATTERING OF LIGHT IN LIQUIDS

HAL Id: jpa-00214927

https://hal.archives-ouvertes.fr/jpa-00214927

Submitted on 1 Jan 1972

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

THERMAL AND STIMULATED MOLECULAR SCATTERING OF LIGHT IN LIQUIDS

I. Fabelinskii, V. Starunov

To cite this version:

I. Fabelinskii, V. Starunov. THERMAL AND STIMULATED MOLECULAR SCATTERING OF LIGHT IN LIQUIDS. Journal de Physique Colloques, 1972, 33 (C1), pp.C1-215-C1-219.

�10.1051/jphyscol:1972137�. �jpa-00214927�

JOURNAL DE PHYSIQUE Colloque C1, supplkment au no 2-3, Tome 33, Fkvrier-Mars 1972, page C1-215

THERMAL AND STIMULATED MOLECULAR SCATTERING OF LIGHT IN LIQUIDS

I. L.

FABELINSKII and V.

S.

STARUNOV P. N. Lebedev Physical Institute, Moscow,

U.

S. S. R.

Rdsum6. - On ktudie la dkpendance en fonction de la tempkrature du spectre de la lumiere diffu- s6e par les fluctuations d'anisotropie dans des liquides (salol et benzophknone). On observe deux branches pour l'kcartement entre les composantes du doublet dii aux ondes transverses. I1 y a branche a basse temperature, pour laquelle l'ecartement entre composantes decroit quand la temp&

rature croit, et il y a une branche

a

haute temperature, pour laquelle l'ecartement dkcroit quand la tempkrature decroit. Dans les ailes de la raie Rayleigh des liquides que nous avons ktudiks, on peut distinguer deux lorentziennes dont les largeurs different de deux ordres de grandeur. On definit deux temps de relaxation a partir de ces donnks. En se servant de ces mesures et des donn6es de la dependance en fonction de la tempkrature d'un autre parametre, on montre que la thBorie de Rytov avec deux temps de relaxation pour I'anisotropie dkcrit trks bien la dependance en fonction de la temperature de l'kcartement entre les composantes de la structure fine des ailes de la raie Rayleigh.

On a aussi mesure le gain di3 la diffusion Rayleigh stimulke depolaris6e. On a observe le ph6nomhne de la diffusion thermique stimulee due a I'effet Blectrocalorique dans les liquides qu'on a etudi6s.

Abstract.

-

The temperature dependence of the spectrum of the light scattered by anisotropy fluctuations is studied in liquids (salol and benzophenone). Two branches are observed in the temperature dependence of the splitting between the components of the doublet induced by shear waves. There is a low temperature branch, in which the splitting between thecompoments decreases when temperature increases, and there is a high temperature branch, in which this splitting decreases when temperature decreases. In the Rayleigh line wing of the liquids that were studied one can distinguish two lorentzians the width of which differed by two orders. Two relaxation times and their temperature dependence are defined from these data. With the use of these measurements and data of the temperature dependence of an other parameter it is shown that Rytov's theory with two times of anisotropy relaxation describes very well the temperature behaviour of the splitting between components of Rayleigh wing fine structure.

The gain of stimulated Rayleigh line wing light scattering is measured as well. The phenomenon of stimulated temperature light scattering due to an electrocalorical effect is observed in the liquids that were studied.

Laser application in the investigations of physical optics led to the discovery of several new phenomena.

Particularly, many good results have been obtained these recent years

in

the study of thermal and stimu- lated molecular scattering of light [I], [4]. The number of works in this field is ever growing.

Some recent results of the authors and their collea- gues will be under discussion in this paper concerning the studies of spectra of thermal depolarized light scattering, stimulated light scattering in Rayleigh line wing, and stimulated entropy or temperature scatter- ing of light.

Fine structure of Rayleigh line wing. - The fine structure in the spectrum of thermal depolarized scattering of light (fine structure of Rayleigh line wing (FSW)) was first observed and interpreted by Tiganov and the authors [5]. The new phenomenon implies that a doublet can be observed for certain polarizations of exciting and scattered light in the

spectrum of the Rayleigh line wing. This phenomenon occurs due t o scattering of light by anisotropy fluctua- tions produced by the fluctuations of deformations (shear waves) [5]. This interpretation was proved by the studies of polarization, angular and light frequency dependence of FSW component shift

[ 5 ] ,

[6], [7], [S],

~91.

In the first temperature investigations it was found unexpectedly that when the temperature decreases the interval between the FSW components does not increase and even decreases [5], [6].

The further experiments made by Sabirov and the authors [8],

[9]

revealed the whole picture of some- what extraordinary temperature dependence of the component shift produced by transverse hypersound.

The diagram of the dependence of intervals between the components of the transverse doublet 2 Av, vs temperature in salol is given in figure

1

for the case when its viscosity changed from

-

^{10' to poise.}

In the temperature range of

-

500C t o

3

OC the

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972137

CI-216 1. L. FABELINSIUI AND V. S. STARUNOV

interval between the transverse components is decreas-

ing when the temperature increases, as it was expected from the Maxwell scheme of viscosity and the Leon- tovich theory with one relaxation time [I].

FIG. 1.

-

Temperature dependence of splittings between the FSW components in liquid salol.

-

theory, 0 experiment.

In the temperature range of 3 OC to 45 OC the doublet was not observed. In the temperature range of 45 OC to 120 OC FSW was observed, the distance between the FSW components was increasing when the tempe- rature increases. The same dependence of Av, upon t was observed by Sabirov and the authors for the case of benzophenone.

We showed in [8] that the described character of

Av, dependence vs t

could be qualitatively explained if one supposed the existence of two processes of fluctuation dissipation with different relaxation times

7,

and z2

(2,

> 2,).

The 'theoretical calculation of light scattering anisotropy fluctuations with the account of two relaxa- tion times has been recently performed by Volterra [lo], Rytov [Ill and Romanov and Solovyev [12].

If in the general Rytov's theory one assumes the same dispersion law for optoelastic coefficient X(o) as for shear modulus i ( o ) the following equation for the intensity distribution can be obtained [13]

:

Here

X,, p, are the optoelastic coefficient and the

shear modulus for o

-+ co. 490, p

are the shear viscosity and the density, z,

=

yo/p,, (2,

2

z,

2 z2), 0 is

the angle of scattering. q

=

2 K sin

912

where K is wave-number of the exciting light. T and R are repre- sented as following

:

The first term in eq. (1) is responsible for arising of the shear components in the light scattering. Let us introduce the symbol y

=

(52; T:)-~, where

/.. 1 %

In the case of

y

4 z1/(zM - 7,) (large viscosity) and z2 4 z, the first term in eq. (1) have the maximum at frequency

:

In the case of

y $- ---

" (small viscosity) and (ZM - ^{~ 2 )}

z,

4

2,

one can get

:

Thus the shear components shift at large viscosity is determined by the limit sheam modulus value p,. At low viscosity it is determined by the cr partial

))

modulus p1

=

qo/z,.

The transition from the first case to the second one takes place in the temperature region in which

In this temperature region the relaxation background of the scattering light essentially influence on the shear components position. This influence must be taken into account if one compares the experimental results with the theory. In the transition temperature region (y -- y,,) the FSW components cannot be observed at all because of the relaxation background influence.

For comparing the experimental results with the

theory we studied the tempe:rature dependence of the

relaxation times

z,

and

^2,

in salol and benzophenone

and obtained the temperature dependence of another

parameter as well. The result of the calculation of the

components shift temperature dependence fulfilled

by us with the use these data according to eq. (I), is

given in figure 1 by the solid curve. The quite satisfac-

tory qualitative and quantitative agreement of the

THERMAL AND STIMULATED MOLECULAR SCATTERING OF LIGHT IN LIQUIDS C1-217

nitrobenzene

(' =

i800)' In this work the exciting

_{FIG. 3. -} Observation of pimseCond pulses of radiation at

light laser - 150 MWt was focused

SWS in nitrobenzene. 1. Observation scheme. Terms : F : inter-

into the vessel with nitrobenzene by using lenses with

ferential filter, FP : Fabry-Perot interferometer, Rd : the vessel

focus off

=

1.5 cm and

f = 3

cm. The spectrum of

with rodamin 6 G, M : is the mirror ( R 100 %). 2. Spectrum

the sws light scattered backwards was a wide band of

of stimulated light scattering in nitrobenzen. Scattering angle 0 = 180°. Dispersion region of the Fabry-Perot interferometer

cm-l to from the Stokes side

_{is 5 cm-l. 3,} Pictures of tracks of two-photon luminescence.

having a spreading-out maximum of intensity in the

_a) exciting radiation, b) radiation of SWS. W : is the maximum

range of - ^{0.4 + 0.5 cm-I.}

of two-photon luminescence.

results calculation with the experimental data takes place in the high temperature range. The discrepancy

_fh

in the low temperature range may be explained by the fact that at large viscosity the relaxation theory formulae must be replaced by nonlocal theory for- mulae. Thus as it seems to us, the nature and the main

-

911

3L1.

feature of the FSW are qualitatively understood.

Stimulated scattering

of light in the Rayleigh line

wing. -In the first paper [14] and our later papers [15], [16] we mentioned that in the spectrum of stimulated light scattering in the Rayleigh line wing (SWS) a wide Stokes wing often occurs instead of the line shifted along the frequency to the Stokes direc- tion by the value o

=

l/z (z is the relaxation time of

anisotropy). The later investigations displayed the

^{~4 q+t} wf ga$ t 2

a9 EN-'

following possible causes of appearance of the wide

spectrum in sws 1) saturation in orientation of

^{FIG. 2.}

-

Dependence of relative coefficient of SWS amplifica- tion upon the frequency o = wo - wl. 0 : the circular polari-

axis of anisotropic molecules at high intensities of

_{,ation of laser} radiation ; ⁺ : the linear polarization of laser

light wave fields 1171, [I81

;

2) the process of four-

radiation. The measured maximum of the SWS coefficient

photon interaction [19], [20]

;

the multi-mode struc-

amplification gk,, ^{= 5}

x

10-3 cm/MWt, calculated value is

ture of exciting radiation [21]

;

the self-modulation of

gk,, = 5.7 x 10-3 c m / ~ W t .

laser radiation [22] ; the formation of short picosecond

pulses in the process of SWS

[23].

All above causes In figure is the scheme of of two- may lead to broadening and spreading out of the photon luminescence in rodamine-solution

- 6 G

maximum in the SWS spectrum at high intensities and pictures of two-photon luminescence tracks with of the exciting radiation. small intensities of the the use of illumination by exciting radiation and exciting radiation according to the theory [Id], [24] SWS one. The maximum of two-~hoton luminescence the coefficient of SWS amplification has its maximum

at the frequency w,

=

o0

-

l/z where o0 and o , , are the frequencies of exciting and scattered light, respectively.

In our laboratory Vlasov made measurements of the SWS amplification coefficient as a function of o

⁼

o0 - w, in o-xylene with the pumping being

-

^10'

MWt/cm2. The technique .of measurements was similar to that used for this by Denariez and Bret [25]. The measurements were made for both circular and linear polarizations of pumping light.

The results are in figure 2. The dependence of ampli- fication coefficients upon Av, their value and maximum position well agree with the theory.

As it was mentioned before at high amplification coefficient ultra-short picosecond pulses of radiation (PP) may appear. The most effective is the process when the scattering is backwards (0

=

1800). In the case of stimulated combinations scattering PP was observed by Maier and Kaiser 1261.

Kyzylasov and one of the authors [23] used the technique of two-photon luminescence and detected

ultra-short pulses during the SWS scattered backwards

^{FIG. 3.}

Cl-218 I. L. FABELINSKII AND V. S. STARUNOV

(contrast - 2) in the picture makes us suppose that

in the scattered light there were more than two PP with life-times - ^{10- s.}

Earlier we observed

[15]

that in case when a Stokes widening of SWS occurs, the SMBS phenomenon is suppressed. This competition can be explained by the fact that the energy density in the range of non-linear interaction is periodically changing with a period that is less than the life-time of acoustic phonons. So, the SMBS phenomenon has too little time to develop.

Stimulated entropy (temperature) scattering

of

light.

-

In the first report about the phenomenon of sti- mulated enthropy (temperature) light scattering [27]

(STS) we did not speak of any detailed spectral investigations of STS line shift though the whole phenomenon was proved definitely STS was observed in pure benzene. So it was accounted for by the electrocalorical effect.

The further theoretical [28], [29] and experimental investigations showed that beside STS (STS-I) caused by electrocalorical effect there becomes possible a scattering caused by light absorption (STS-11). The line STS-I is expected to shift to the Stokes direction while the STS-I1 toward the anti-Stokes side respective to the frequency a,.

The spectral studies allowed to observe STS-I in gases [30] and STS-I1 in liquids and gases [31], [32].

Recently Kyzylasov and the authors managed to observe STS-I in pure liquids [33].

It follows from the stationary theory for the STS amplification coefficient that [29].

should appear, and at high 2 K, STS-I1 ought to occur. Thus, to observe STS-I in liquids the light absorption coefficient must be minimized.

STS-I was observed in a 1.horoughly cleaned ben- zene and absolute ethyl alcohol.

The exciting radiation of - ^{50 +} 80 MWt was focused on the medium by means of a cylindrical lens. The studies of Iight distribution within the lens focus showed that there are regions

(--

20 p thick) of high concentrations of light energy.

The scattered radiation was observed at the angle

~9 =

900 respective to the direction of radiation dis- tribution. The spectral composition of scattered radiation was analyzed with the help of a Fabry- Perot interferometer. Along with the scattered radia- tion the spectrum of exciting radiation (etalon beam) was photographed through the same optical system and photoplate. The polarization of the beam of comparison was turned to the angle 900 respective to the polarization of the scattered radiation so that the system of analyzers made it possible to obtain a spectrum of exciting radiation on one side of inter- ferogram and a STS-spectrum on the other.

In figure 4b is given a spectrum of STS obtained in pure absolute alcohol. The comparison of these spectra (Fig. 4a, b) shows that the STS line is shifted to the Stokes direction (STS-1). Addition of the light absorber (J2) into the liquid causes a STS line shift toward to the anti-Stokes direction (STS-11) (Fig. 4c).

The following terms are included here

:

w = a o

-

a l , q = K O - K , ,

o1

and Kl are 'the frequency and wave vector of the scattered light, C and 2 K, are the velocity and coefficient of light absorption, x and

C p

are the tem- perature conductivity and thermocapacity of the medium, T is the absolute temperature. For the

spectrum

of

exciting radiation we took a L~~~~~~

^{FIG. 4. -} STS spectrum in ethyl alcohol : a) the spectrum of

distribution

: exciting radiation ; b) the STS-I spectrum ; c) the STS-I1 spec- trum ; TI and T I 1 are the lines of S,TS-I and STS-XI, respectively.

As it follows from (3) at When the power is increased in pure benzene a STS-I1 line appears instead of the STS-I line. In this 2 K , < - 1

T~~~

1 $ 1 ^STS-I case the non-linear light absorption starts, perhaps,

2 nc to influence the STS phenomenon.

THERMAL AND STIMULATED MOLECULAR SCATTERING OF LIGHT IN LIQUIDS C1-219

References [I] FABELINSKII (I. L.), Molecular scattering of light,

Plenum Press, N. Y., 1968.

[21 FABELINSKII (I. I.), STARUNOV (V. S.), Appl. Opt.,

- . - -

1967,6,1793.

[3] STARUNOV (V. S.), FABELINSKII (I. L.), UFN, 1969, 98, 441.

[4] Light scattering spectra of solids, Proceedings, Conference on Light Scattering Spectra of Solids, Springer-Verlag, New York, Inc., 1969.

[5] STARUNOV (V. S.), TIGANOV (E. V.), FABELINSKII (I. L.), Pis'ma JETP, 1967,5,317.

[6] STEGEMAN (G. I. A.), STOICHEFF (B. P.), Phys. Rev.

Letters, 1968, 21, 102.

[7] SABIROV (L. M.), STARUNOV (V. S.), FABELIN-

SKII (I. L.), Pis'ma JETP, 1968, 8, 399.

[8] FABELINSK~I (I. L.), SABIROV (L. M.), STARUNOV (V. S.), Phys. Letters, 1969, 29A, 414.

[9] SABIROV (L. M.), STARUNOV (V. S.), FABELIN- sKrr (I. L.), JETP, 1971,60,146.

1101 VOLTERRA (V.), Phys. Rev., 1969,180, 156.

[ l l ] RYTOV (S. M.), JETP, 1970, 58, 2154 ; 1970, 59, 12.

[12] ROMANOV (V. P.), SOLOVYEV (V. A.), Optica i Spec- troscopy, 1970,29,884.

[13] STARUNOV (V. S.), JETP, 1971 61, 1583.

1141 MASH (D. I.), MOROZOV (V. V.), STARUNOV (V. S.), FABELINSKII (I. L.), Pis'ma JETP, 1965, 1, 41.

[15] ZAITZEV (G. I.), KYZYLASOV (Yu. I.), STARU-

NOV (V. S.), FABELINSKII (I. L.), Pis'rna JETP, 1967,6,505.

[16] KYZYLASOV (Yu. I.), STARUNOV (V. S.), FABELIN-

SKII (I. L.), Pis'ma JETP, 1969,9, 383.

[17] FOLTZ (N. D.), CHO (C. W.), RANK @. H.), WIG-

GINS (T. A.), Phys. Rev., 1968,165,396.

[18] HERMAN (R. M.), Phys. Rev., 1967, 164, 200.

[19] ZAITZEV (F. I.), K Y Z ~ A S O V (Yu. I.), STARUNOV (V. S.), FABELINSKU (I. L.), Pis'ma JETP, 1967, 6, 695.

[20] CHIAO (R. Y.), and GODINE (J.), Phys. Rev., 1969, 185,430.

[21] BLOEMBERGEN

(N.),

LALLEMAND (P.), Phys. Rev.

Letters, 1966,16,81.

(221 OSTROVSKII (L. A.), JETP, Pis'ma, 1967, 6, 807.

[23] KYZYLASOV (Yu. I.), STARUNOV (V. S.), Pis'ma JETP, 1969, 9, 648.

[24] STARUNOV (V. S.), DAN USSR, 1968,179, 65.

[25] DENARIEZ (M.), BRET (G.), Phys. Rev., 1968,171, 160.

[26] MAIER (M.), KAISER (W.), Phys. Rev. Letters, 1966, 17,1275.

[27] ZAITZE" (G. I.), KYZYLASOV (Yu. I.), STARUNOV

(V.

S.), FABELINSKII (I. L.), Pis'ma JETP, 1967,6,82.

[28] HERMAN (R. M.), GRAY (M. A.), Phys. Rev. Letters, 1967,19,324.

[29] STARUNOV (V. S.), JETP, 1969,57,1012.

[30] FABELINSKII (I. L.), MASH (D. I.), MOROZOV (V. V.), STARUNOV (V. S.), Phys. Letters, 1968, 27A, 253.

[31] RANK (D. H.), CHO (C. W.), FOLTZ (N. D.), WIG-

GINS (T. A.), Phys. Rev. Letters, 1967, 19, 828.

[32] WIGGINS (T. A.), CHO (C. W.), DIETZ (D. R.), FOLTZ (N. D.), Phys. Rev. Letters, 1968, 20, 821.

[33] KYZYLASOV (Yu. I.), STARUNOV (V. S.), FABELIN-

SKII (I. L.), Pis'ma JETP, 1970,11,110.