Second order dipole absorption in ionic crystals

184

LATTICE

C12.

CONFERENCE

INFRARED ABSORPTION BANDS AT FREQUENCIES IN CUBIC CRYSTAL D.W.

Berreman

Absorption

(Bell

of i n f r a r e d

strong

peaks

at

optic

(L.O.)

modes

as w e l l

when

the

incident

absorption

bands

substrata

and

of a f i l m

of

measured,

but

These

the the

temperatures

of

with

constant, film

disappears

deposition

of

C13.

LATTICE

from

and

when

6i a r e

optic

mode

SrF2,

L.O. the

The

substrata

substrata

with

is

substrata

is u s e d .

macroscopic

frequencies.

deposited

and

L.0.

at h i E h

in reflectance

at

room

temperature,

imaginary

film.

is

between

absorption

real

each

L.0.

transmittance

substrata

relationship

measured

for

with

the

the

polar

obtained

a metal

crystals

on a m e t a l

the

equations

Jersey)

frequencies

surface.

than when

6

longitudinal

(T.O.)

film

New

of c u b i c

on a t r a n s p a r e n t

CaF 2 and were

films

i No.

MODE

Hill,

is d e p o s i t e d

when

approximate

£r a n d

thickness

deposition

the

Glass,

were

the

deposited

and

OPTIC

Murray

optic

film

from Maxwell's

of a n

~i/(62r + £2i) w h e r e

dielectric

to

disappears

Vol.

lon G wavelength

is m e a s u r e d ,

of LiF,

coated

Curves

of

the

long wavelength

of f i l m s

on R h

temperature.

when

conditions

and

bands

band

flat

transverse

normal

thickness

derivable

boundary

absorption

is n o t

reflectance same

are

polarizability

at

TITLES

LONGITUDINAL

by

frequencies as

AND

Laboratories,

radiation

stronger

the T.O.

effects

electrical

the

beam are

POLAR FILMS

Telephone

shows

=

ABSTRACTS

parts

An apparent

temperature

during

sufficiently

hot

of the

variation film

during

films.

VIBRATIONS

OF L a C l 3 A N D

LaBr 3 FROM VIBRONIC

S P E C T R A 28

I. R i e h m a n , R.A. S a t t e n a n d E.Y. W o n g ( D e p a r t m e n t of P h y s i c s , University of C a l i f o r n i a , Los A n g e l e s , C a l i f o r n i a ~ .

C14.

SECOND B.

ORDER

Szigeti

order

dipole

the

infra-red

relation

28.

To be

ABSORPTION

(Department

A relation

second-order

DIPOLE

IN

of P h y s i c s ,

is d e r i v e d

for

the

absorption

in

a considerable

absorption

is b a s e d

published

alkali

in

essentially

in

J°

the on

Chem.

CRYSTALS

University

order

dipole

has

IONIC

halidee.

of m a g n i t u d e The

The

two a s s u m p t i o n s ,

Phys.

of the

relation

importance

side-bands.

of R e a d i n g ,

on

England) second-

shows

tha~

the m a g n i t u d e

derivation both

of

of w h i c h

the are

the of

Vol.

i No.

fairly

6

LATTICE

generally

accepted

~lectron

deformation

internal

electric

to

the

be

obtained

elementary

Our

from

field;

(ii) so

the

or s i l i c o n , than

considerations of very

C15.

the

contradicted

the

which

slde-band

indicate

different

by is

that

magnitude

the

the

fact

to the

absorption

the

the

two-phonon

dipole

only,

absorption

can

infrared

lation

as

sorption

optical

Fourier

function.

dipole cubic

the

In

coefficient

moment

of

discussion

paper

from

the

terms

the

in

plane.

out

through

and

Ward.

the

The

the

the

solution

required

cient

given

of the

in

terms

integral

also

be

the

real

used

in

29.

Westinghouse

30°

U.S.

Naval

calculation

equation

Research Research

terms

the in

potential function

continuation

of

the

of a n

of

becomes

in t h i s

frequency

in

the

function

equation

in

The

in

is

two

coefficients.

axis

carried

complex

the

this

Pittsburgh

Washington

25,

35, D.C.

of

of L u t t i n g e r

means

is

the

complex

absorption

which

developed

of

presence

of a d o u b l e coeffisolution

paper

can

In some

a Boltzmarnl equation.

Laboratories,

Laboratory,

the

propagators

density,

ab-

Fourier

function.

transport

the

The

out b y

methods

corre-

appears

is c a r r i e d

spectral The

vertex

can be

expansion

real

points

dependent

integral

to

ORDER

Institute

moment

energy. which

to the

discrete

the v e r t e x

equation.

the

integral

in

displacements,

crystal

at

dipole

contribution

Green's

continuation of

the

(Carnegie

of a c r y s t a l

crystal

order

temperature

representation

is

study

atomic

only

spectral

of a r e a l

we

determination

of

the

as

defined

The use

It is

variables.

the

two-particle

function

coefficient

of the

second

of the

is e x p r e s s e d

of a v e r t e x frequency

this

in p o w e r s

anharmonic

transform

absorption

transform

be

of s o l i d .

J . S . L a n g e r , A . A . M a r a d u d i n 29 a n d R . F . W a l l i s 30 of T e c h n o l o g y , P i t t s b u r g h 13, P e n n s y l v a n i a ) The

is

Various

ON THE INTERACTION BETWEEN CUBIC ANHARMONICITY AND A SECOND ELECTRIC MOMENT IN THE OPTICAL ABSORPTION OF C R Y S T A L S

expressed

can

absorption

dipole

crystals.

dipole

types

equal

dipole

second-order

second-order ionic

the

the

charge.

of the

second-order

in d i f f e r e n t

(i) and

deformation

effective

in

are:

repulsion

is a p p r o x i m a t e l y

order

that

185

These

charge

magnitude

due

TITLES

overlap

first

of

the

AM)

halides. by

static t~e

value

concerning

is n o t

alkali mainly

that

measured

in diamond

ABSTRACTS

the

charge,

conclusion

weaker

for

is g o v e r n e d

absorption

much

CONFERENCE

Pennsylvania.

cases