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POLARIZATION FILTERING IN HOLOGRAPHY

C. L. Rudder

Citation: Applied Physics Letters 10, 270 (1967); doi: 10.1063/1.1754806

View online: http://dx.doi.org/10.1063/1.1754806

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2/4

Volume

10,

Number

10 APPLIED

PHYSICS LETTERS

15 May 1967

Table I.

Spectrometer Performance at 77K

y-ray

Detector

Ser.

Area

Depth

Resolution(

Energy

Bias

Designation

No.

(em

2

) mm) Trapping (4E)\t (keV) (keV) (V) Rating

UA

G3Pl 4.2 6

electron

1.4

662

1200 good

(little)

2.6 600

B

7012 8.5 7

electron 3.35

1333 1250 fair

(moderate) 4.95

700

e

GLN4L

5.8 8

electron 5.5 1333 1250

very

(considerable) 7.0 800

poor

(')From measurements of a very good detector, the values

of

(4E)0 were, respectively, 1.2

and

1.7 keY

for

662

and

1333 keY y-ray

energies

for

all electric fields ;;.100 V

mm

(b 4E)0 see text).

ating voltage (2700 V) in order to eliminate the

slow rising

components,

the lowest temperature

for

high-resolution performance was

lOoK.

Figure

2 also shows

that

there is a slight

decrease

in pulse

height

as temperature is reduced,

corre

sponding to

an

apparent increase in e, the ionization

energy per

electron-hole pair.

For detector

A,

the

increase was 1.9%

in going

from

170

to lOoK.6 This

change in e with temperature is much less than that

reported by

Emery and

Rabson.

7

Capacitance-voltage characteristics were meas

ured over the entire temperature range and in

dicated no significant

change in

detector-sensitive

volume

with

temperature.

In

summary,

we

conclude

that

one can expect

less

low

energy

tailing and therefore better ')I-ray resolu

tion from

many

Ge(Li)

detectors

by operating them

at

temperatures lower

than

-77K (that of liquid

nitrogen, and

now

commonly

used); the optimum

temperature

of

three

detectors of

varying quality

showing

mainly

electron

trapping was in the range

20 to 30

o

K. Electron

trapping effects are

reduced at

lower temperatures and

can be

further reduced by

applying

higher voltages

than

are possible at -77K.

The cause

of a slow-rising component of

the

pulse

which appears below

200K

is still under study.

No

advantage is gained by operation above 77K (e.g.,

dry

ice

at 195K)

because the reverse

current

in

creases with temperature

resulting

in deterioration

of the observed ')I-ray resolution.

Measurements

are

continuous

on

other

detectors showing

predomi

nantly hole trapping and on very

good

detectors

exhibiting very little trapping of either electrons

or

holes at 77K.

We express our thanks

to 1. L. Fowler

for

his

help

and encouragement with these

experiments.

I A.

J.

Tavendale,

IEEE

Trans. NS-ll,

3,

191 (1964).

2 M. M. El-shishini

and

W

.

Zobel,

IEEEE

Trans. NS-13,

3,

359

(1966).

3

A.

J.

Tavendale

and I.

L. Fowler, unpublished Chalk River

data (1964).

4 F.

S.

Goulding, Nucl. Instr. and Methods 43, 1 (1966).

5J.

A.

Coleman, Lithium-Drifted Germanium Detectors, IAEA,

Vienna (1966), p. 37.

6E. Sakai, unpublished.

1 F.

E

Emery

and T.

A. Rabson,

Phys.

Rev. 140, A2089 (1965).

POLARIZATION FILTERING

IN

HOLOGRAPHY

C. L. Rudder

Reconnaissance Laboratory

McDonnell Aircraft Corp.

St. Louis, Missouri

(Received 20 March 1967)

The

effect of specular reflections

on

the construction of a hologram is examined by polarization filtering. Filtering

is accomplished by orienting the plane of polarization of the reference wave perpendicular to that of the incident

object beam.

t is found that the

resolution

and

tonal

range

of

the

reconstructed image

are

enhanced.

Light scattered

from a rough

surface

is

described component. Specular

reflections are directional

as

the sum

of

a

specular

component

and

a diffuse .

and

retain, at

least in

part, the

polarization

of

the

270


129.81.226.78 On: Tue, 26 Aug 2014 15:06:33


3/4

Volume

10,

Number 10

APPLIED PHYSICS LETTERS

15 May 1967

incident light.

When

the incident wave is linearly

polarized with the electric vector either parallel

or perpendicular

to

the scattering surface, the

specular

reRection will preserve the

incident

polari

zation. However, the diffuse contribution has little

directivity and gives rise to depolarization.

In

constructing holograms,

these

considerations are

important

since

merely producing

a reconstructed

image of the object as

seen

visually

can

destroy

desira9le

information.

This Letter reports the

effect of selective

polari

zation filtering

during

construction of a hologram.

In particular, it has

been

found

that

the resolu

tion

and

tonal

range

of

the reconstructed image are

enhanced

by eliminating

the recording

of specular

reflections.

Filtering was accomplished by rotating

the

polarization )f

the reference beam

with

re

spect

to

the

polarization

of

the incident

object

beam. The

experimental setup

for this study is

depicted in Fig. I. The polarization of

the

incident

object beam

was

selected for

maximum

transmit

tancethrough the

light

polarizing

film

Rausch

and

Lomb

type H:\,-:18). The

angle

of polarization of the

reference wave was established by a second polarizer

as indicated. The

neutral

density filter was

selected

to

maintain

a constant intensity ratio

between

the

two beams.

This

was necessary since

the

initial

elliptical polarization caused variations in light

intensity

when

the polarizer in the reference beam

was

rotated

to

different

positions.

The object was composed

of

five scattering areas

designed

to

determine image

quality.

An eleven

step Kodak gray scale

on

single-weight

semi-matte

paper was chosen for tonal range; a National Bureau

of

Standards

resolution

chart

on single-weight

matte

paper

and the letter on single-weight

semi

matte paper were used for

resolution;

and

a

strip

Elliptically

polarized

Laser

light

dens ity

i

Iter

Fig.

1.

Diagram of

the

laboratory

setup for

polarization

filtering.

of

aluminized mylar

was

used

to provide

an

area

of particularly high reflectivity. The latter was

placed to give

specular reflections from irregular

bumps rather than

a smooth

mirror-like

reflection.

Finally, a piece of black

photographic

tape at the

right of the

furnished

a

very rough,

low-reflection

area.

Thus, the

object

encompassed the pertinent

parameters

for image evaluation.

Holograms discussed

herein

were made

with

the

object

illuminated with

laser light

at 6328

A po

larized with the electric vector parallel to the object

plane. Reconstruction of the virtual image for

the

case

of

a

hologram made

with

the

polarization

of

the reference beam

and incident

object beam parallel

is

shown

in Fig. 2. A severe

degradation

of

image

quality is evident except on the

edge

of the specular

area. Here the image appears

to

be clouded but

prominent.

I n fact,

the

image

is

similar

to

viewing

the object by eye

under

the

same

conditions.

Figure 3 shows the virtual

image

from a holo-

Fig. 2.

Image from the

hologram

constructed

with

specular

and diffuse

scattering recorded.

Fig. 3.

Image from

the hologram

constructed with the

specular component

filtered out.

271


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4/4

Volume

10,

Number 10

APPLIED PHYSICS LETTERS

15

May

1967

gram constructed with

the

reference beam and in

cident object beam linearly

polarized

orthogonally

to

each

other.

The specular

return has been filtered

out, thereby significantly improving the image

quality.

The

holograms

were

made on Kodak

649F

plates. Prior to exposure, the light intensity from

each beam was

measured independently and com

bined

at the plate holder to maintain a

constant

intensity ratio for successive plates. Also, this

procedure

permitted

the

exposure time for

con

secutive holograms to

remain

fixed. Exposure

and

development processes were the

same

for the

photo-

graphs displayed in Figs. 1

and

2

Therefore, dif

ferences

seen in the

hologram images can be

attributed only

to

polarization filtering. The results

clearly

demonstrate that the method

can be

useful

in preventing loss of information recorded by ho

lography.

The author

acknowledges

the

valuable assistance

of W. A.

J

Dalton and R L Carpenter.

I

Petr Beckmann

and Andre

Spizzichino, The Scattering of

Electromagnetic Waves from Rough Surfaces (The

Macmillan Com

pany, New York, 1963), 1st ed., pp. 152,241.

NONLINEAR COUPLING

BETWEEN ANTIFERROMAGNETIC

RESONANCE MODES IN RhMnFa*

P H

Cole

Department

of Electrical

Engineering and

Center for

Materials Science

and

Engineering

Massachusetts Institute of Technology

Cambridge, Massachusetts

Nonlinear coupling between antiferromagnetic resonance modes spaced in frequency an octave apart has been

shown to occur under suitable conditions in RbMnF

a

. Calculations of the power-dependent conversion relation

for up conversion,

and

the critical power for

subharmonic

oscillation,

are

given. Preliminary

measurements

of the

strength

of

the second-harmonic power

produced are

in

general

agreement with the theory, but the shape

of

the

output

pulses suggests some spin-wave excitation

is

taking place.

The magnetic resonance spectrum of the cubic

antiferromagnet

RbMnF

has been

shown

in

the

low-

and

high-field regionsl,2 to

have

modes which

may

bear an octave relation

to

one another. The

mode spectrum when

the

applied field

Ho

is along

a (001) axis, calculated for

an

exchange field

e

0.89 MOe, an

anisotropy

field Ha = 4.56 Oe and a

nuclear hyperfine field

Hn

= 1.0 Oe, is shown in

Fig. 1

Second-order spin-wave instability effects, as

sociated with

the

excitation

of

spin waves of the

same frequency as

the

power source

have been

shown

to occur in this and similar materials.

3

4

These

instabilities can be considered as analogous to the

second-order instabilities

in

ferromagnets explained

by SuhJ.5 Calculations by

Freiser

et

aU

have

sug

gested

that

first-order nonlinear w - w energy

conversion

processes should also occur. The latter

processes might

be

considered as

analogous

to

the

*This work was

supported

in part by

the

Air Force Cambridge

Research Laboratories

under Contract

AF 19(628)-5876

and

by

the

Advanced Research Projects Agency

under

Contra ct SD-90.

272

25

Ho=4 56 Oe

N

Hn= 1.0 Oe

J

He=0 89

MOe

)

20

u

z

w

>

15

w

0::

LL

10

z

0

CJ

W

0::

5

o

8

Ho

KOe

Fig.

1.

Resonance

spectmm

of

a

sample

of

RbMnF

a

at

10 K.


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