Construction of a magneto-optic shutter utilizing the Faraday effect

Rochester Institute of Technology

RIT Scholar Works

Theses

Thesis/Dissertation Collections

1971

Construction of a magneto-optic shutter utilizing

the Faraday effect

Christian Bergerson

Richard Leary

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CONSTRUCTION

OP

A

MAGNETO-OPTIC

SHUTTER

UTILIZING

THE

FARADAY

EFFECT

by

Christian

Bergerson

Richard

J.

Leary

An

Abstract

College

of

Graphic

Arts

and

Photography

School

of

Photgraphic

Arts

and

Sciences

Department

of

Photographic

Science

and

Instrumentation

June-

1971

ACKNOWLEDGEMENTS

We

wish

to

thank

the

following

people

for

their

assistance:

C.

W.

Bergerson

Electrical

Instrument

Labs

J.

C.

Carson

Rochester

Institute

of

Technology

J.

B.

Helm

Corning

Glass

Works,

Inc.

Mrs.

Lynch

Ilex

Corporation

R.

N.

Norman

Rochester

Institute

of

Technology

D.

C.

Robinson

Rochester

Institute

of

Technology

E.

W.

Schumann

Rochester

Institute

of

Technology

Also

the

works of

H.

E.

Edgerton,

K.

J.

Germeshausena

and

C.

W,

Wyckoff

were used as

the

basis

for

the

entire project.

TABLE

OF

CONTENTS

Page

List

of

Figures

v

List

of

Symbols

vi

Abstract

Introduction

1

Theory

of

the

Magneto-Optic

Shutter

2

Filter-Glass

Combination

4

Description

of

Triggering

Circuit

5

High

Voltage

Circuit

8

Calculating

the

Angle

the

Plane

of

Light

is

Rotated

10

Operating

Instructions

13

Summation

and

Results

16

Discussion

17

Bibliography

LIST

OF

FIGURES

Figure

1

Graph

of

Transmission

vs

Angle

between

axes of

transmission

for

HN22

Polarizing

Material

2

Optical

Components

of

the

Shutter

3

Photograph

of

Components

of

Shutter

System

4

Graph

of

Wavelength

vs

Transmission

for

HN22

Polarizing

Material

5

Photograph

of

Electronics

Portion

of

Shutter

6

Schematic

of

High

Voltage

Circuit

LIST

OF

SYMBOLS

AND

NOMENCLATURE

0:

The

Angle

of rotation of

the

plane of polarization

(min)

V:

Verdet's

constant (Min-Oer-1

Cm-1)

5:

Length

of coil

surrounding

glass,

approximately

equal

to

length

of path of

light

in

glass

(cm)

H:

Magnetic

field

in

the

center of

the

coil

(oer)

I:

Current

(amps)

W:

Energy

(watt

sec.)

E:

Potential

difference

(volts)

r:

Radius

of coil

(cm)

d:

Diameter

of coil

(cm)

n:

Number

of

turns

per cm

in

the

coil

N:

Total

number of

turns

in

the

coil

L:

Inductance

(henries)

C:

Capacitance

(farades)

u:

Magnetic

permability

(4TT'x

10~"

Webers-Amp--1-Meter--'-)

ABSTRACT

An

attempt was made

to

construct a magneto-optic shutter

utalizing

the

Faraday

effect.

Unfortunately,

the

final

test

ing

did

not show

the

present of

this

effect.

Included

in

the

paper

is

a graph

showing

the

transmission

of.

two

polarizing

filters

vs

the

angle

between

the

transmission

axes of each

INTRODUCTION

The

purpose of

constructing

a

Magneto-Optic

shutter was

to

provide a

teaching

tool

and a short-duration shutter

for

the

Department

of

Photographic

Science,

School

of

Photographic

Arts

and

Sciences,

Rochester

Institute

of

Technology.

Compli-menting

the

construction

is

a

gaining

of skill and

knowledge

THEORY

OF

THE

MAGNETO-OPTIC

SHUTTER

In

1845,

Faraday

discovered

that

when

linear

polarized

light

passes

through

a

homogeneous

medium

in

a

direction

parallel

to

a magnetic

field

which

has

been

established

in

that

medium,

there

will

be

a rotation of

the

plane of polarization of

the

light.

The

angle of such a

rotation,

9,

is

proportional

to

the

strength of

the

magnetic

field,

H,

and

to

the

distance

the

light

passes

through

the

medium,

i

8,

or,

(9

=

V&H)

,

/

6

dEp--(--rrLi^weK^\^'/^-Ay^*A

t

'L.

where

V

is

Verdet's

constant. _cJ-fcx^ -^^a..

}

ret

Qy^6r>6'/C&6

*:

Different

materials exhibit

the

Faraday

effect

to

a greater

or

lesser

degree.

Verdet's

constant

is

used as a measure of

this

property

of a medium and

usually

has

dimensions

of

minutes--cm .

To

utilize

the

effect,

a glass which

has

a

high

Verdet's

constant

is

put

between

two

polarizing

filters

.

The

polari

zing

filters

are oriented such

that

their

axes of

transmis

sion are crossed.

Thus

minimum

light

should

be

transmitted

through

the

glass

filter

combination.

However,

when

the

glass

is

contained within a magnetic

field,

there

is

a rotation of

the

plane of polarization of

longer

effectively

crossed

between

polarizers.

This

allows

the

second polarizer

to

transmit.

Figure

1

shows

the

trans

mission of

two

polarizing

filters

versus

the

angle

between

the

axes of

transmission.

The

magnetic

field

is

induced

by

the

flow

of electrons

through

a coil of wire wrapped around

the

glass .

The

coil

then

functions

as a solenoid.

By

controlling

the

duration

*

of

the

electron

flow,

the

duration

of

the

change

in

transmis

sion of

the

filter-glass

combination can

be

controlled.

The

magneto-optic shutter consists of

two

parts -

the

filter-glass

combination,

and

the

electronic components

necessary

for

the

establishment of

the

magnetic

field.

The

latter

may

be

subdivided

into

the

high

voltage circuit and

the

triggering

circuit.

The

high

voltage circuit provides a po

tential

difference

necessary

for

the

establishment of

the

magnetic

field;

and

the

triggering

circuit provides a means

of

starting

and

stopping

the

flow

of electrons

through

the

coil.

Figure

3

shows components of

the

system.

Figure

2

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FILTER-GLASS

COMBINATION

The

Polaroid

Corporation

supplied us with

two

HN22

po

larizing

filters.

These

filters

have

a

transmission

of

.0005 per cent when

the

axes are

crossed,

and provide

ap

proximately

neutral attenuation of

light.

Sefe

figure

4.

Corning

Glass

Works

supplied a

2.54cm

x

2.54cm

x

7

.62cm

piece of radiation

shielding

material

(Corning 8463)

which

has

a

Verdet's

constant of .

071min-oer~-1--cm~-1-at

700nm,

and

an

index

of refraction of

approximately

1.95>

at

700nm.

Ilex

Corporation

polished

the

ends of

the

piece of glass

to

10

fringes

of

flatness

and parallel

to

within

1.

Mr.

R.

N.

Norman,

of

the

Rochester

Institute

of

Tech

nology,

machined

two

holders

for

the

polarizing

material so

that

the

orientation of each

filter

may

be

adjusted

indepen

dently.

The

filter-glass

combination was enclosed

in

a

large

plexiglass

housing

along

with components of

the

electronic

circuits.

The

housing

for

the

filter-glass

combination

is

isolated

from

the

electronics

by

opaque plexiglass partitions.

Six

coats of

flat

black

paint,

and a

coating

of

black

Suede-Tex

flocking

was

installed

to

make

this

section opaque.

The

purpose of

the

flocking

was

to

minimize

any

internal

reflections

in

this

portion of

the

housing,

and

to

reduce

the

effect of

1

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DESCRIPTION

OF

TRIGGERING

CIRCUIT

The

triggering

circuit

is

essentially

a series of

relay

tubes

set

up

in

a cascade, such

that

it

is

possible

to

apply

a signal at

the

input,

and after an assigned

delay,

achieve a

high

voltage pulse at

the

output,

and after another assigned

delay,

a similar pulse at another output.

Refer

to

figure

6

for

the

following

descussion.

First,

in

the

non-conducting

state of

VI,

there

is

a

negative

bias

on

the

first

grid of

VI,

supplied

through

R3,

R4,

and

R53

and a charge on capacitor

C4.

This

negative

bias

is

sufficient

to

hold

the

tube

in

a

non-conducting

state.

It

should

be

noted

here

that

R3

and

R4

have

been

chosen

solely

on

the

basis

that

maximum current

drawn

from

the

bias

voltage

supply

is

on

the

order of

15ma,

in

order

to

reduce stress on

the

diodes

and/or

transformer.

(Since

the

circuits were ob

tained

from

Dr.

Edgerton's

articles,

and since

he

or

the

editor

omitted certain values of not-too-critical

components,

decisions

similar

to

this

were sometimes

necessary.)

In

the

triggering

of

VI,

the

contacts of

JI

are momen

tarily

shorted

together,

(this

could

be

achieved

through

the

flash

synchronization contacts of a mechanical

shutter)

.

Since

this

is

a

D.C.

circuit,

the

charge stored on

C4

is

removed

for

positive

bias.

The

grid

bias,

then,

will

be

a positive

voltage,

which

is

sufficient

for

the

conduction of

VI.

Normally,

VI

would continue

to

conduct until

the

plate voltage were removed.

This

is

achieved

shortly

after

the

tube

starts

to

conduct,

through

a return

loop

consisting

of

Ll,

C5,

R6,

and

R7

Po

tentiometer

R5

is

used as a

sensitivity

control,

which varies

the

drop

at grid

1

of

VI

as a result of

closing

the

contacts

at

JI.

As

VI

is

conducting,

electrons are

flowing

primarily

from

cathode

to

plate of

VI.

This

causes

the

potential at

grid

1

of

V2

to

drop

to

a

sufficiently

low

value

to

allow

V2

to

conduct.

A

time

delay

is

present

before

V2

conducts,

how

ever,

being

effected

by Ll,

C5,

R7

_,

R8

, and

R9

, with

the

delay

being

adjustable

through

potentiometer

R8

.

Tube

V3

is

biased

through

R17

.

This

bias

is

removed

after a

delay,

(set

by

potentiometer

Rl4).

C9

keeps

this

im

pulse short

to

prevent multiple

firing.

VI,

V2

_, and

V3

are

all

"turned

off"

through

appropriate

capacitor,

and/or re

sistance-inductance

coupling

between

plate and cathode.

The

operation of

V4

is

somewhat

different

in

its

opera

tion

from

VI,

V2,

and

V3

.

It

is

normally

in

a

conducting

state,

since

it

can receive no

D.C.

bias

at

its

grid

because

of

the

fact

that

capacitors

C7

and

CIO

block

any

D.C.

compoment

7

momentarily

by

a negative pulse which

is

initiated

as

V3

con

ducts.

A

delay

is

introduced

at

this

point

also,

through

R11/L2,

C7,

C8,

and

CIO,

with

the

delay

again

being

adjustable

by

means of potentiometer

R15.

J2

represents

the

output

terminals

of

the

triggering

circuit.

As

V3

conducts,

the

potential

difference

between

plate and cathode/screen

drops

rapidly.

Since

the

cathode

is

connected

to

ground,

a pulse will

be

seen

between

terminals

"S",

(start),

and "C"

(common),

since capacitor

C12

will

rapidly

charge

to

this

potential;

the

magnitude of

the

pulse

will

be

very

close

to

the

B+

Voltage

of

the

curcuit .

Simi-larily,

after a pre-set

delay,

a pulse will

be

seen

between

"Q",

(Quench),

and "C" of

the

same magnitude as

the

first

pulse,

but

180 out of

phase,

(i.e.

negative with respect

to

the

start pulse).

These

final

pulses are

then

fed

into

two

separate

step-up

transformers

to

achieve a voltage sufficient

to

initiate

a

spark

to

start and

stop

the

discharging

of

the

capacitors,

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HIGH

VOLTAGE

CIRCUIT

The

high

voltage circuit consists of

a)

the

solenoid sur

rounding

the

glass;

b)

a capacitor

to

store a charge which

is

used as a source of electrons

for

the

establishment of

the

magnetic

field

in

the

solenoid;

c)

and a

transformer-rectifier

combination

providing

a

D.C.

potential

to

charge

the

capacitors.

The

transformer

is

a commercial neon-sign

transformer

having

a

7500rms

A.C.

enter-taped output at

117

volts

A.C.

input.

Only

one-half of

the

secondary

is

used,

since

approximately

4000

volts

peak

D.C.

is

required.

Two

television

focus

rectifiers are

wired

in

series

to

rectify

the

voltage.

Each

of

the

diodes

has

a

240Mn

resistor wired

in

parallel

to

it

in

order

to

pre

vent a

large

current surge

in

the

event of component

failure.

Also,

a current

limiting

resistor

is

wired

in

series with

the

diodes

to

prevent

too

much current

from

being

drawn

from

the

transformer.

(The

transformer

secondary

is

rated at

18

milliamps voltage, and a

4Ma

resistor

limits

the

current

to

1

milliamp

.

)

The

above circuit

is

wired

to

two

0.25uf

capacitors

connected

in

parallel,

providing

a

total

capacitance of

0.5uf.

IT

IS

EXTREMELY

IMPORTANT

NOT

TO

CONNECT

THE

PRIMARY

OP

THE

TRANSFORMER

TO

STANDARD

117

VOLT

A.C.

SOURCE,

SINCE

A

PEAK

9

FOR

THE

CAPACITORS.

THIS

IS

ACHIEVED

BY

USING

A

VARIAC

OR

TRANSFORMER

SUCH

THAT

THE

PRIMARY

VOLTAGE

IS

NO

GREATER

THAN

90

VOLTS.

(PREFERABLY

ABOUT

85

TO

88

VOLTS

A.C.)

See

figure

5

The

capacitors are

discharged

into

the

solenoid across

a spark

gap,

the

spark

being

initiated

by

the

triggering

CALCULATING

THE

ANGLE

THE

PLANE

OF

LIGHT

IS

ROTATED

As

linear

polarized

light

passes

through

the

glass under

the

influence

of a magnetic

field

the

plane of polarization

will

be

rotated.

The

amount of rotation

is

proportioned

to

the

type

of

glass,

the

length

of glass and

the

magnetic

field

The

rotation of

the

plane of polarization

is

I

9

=

VJH

(l)

where:

9

is

the

angle of rotation

in

min.,

1 _i

V

is

Verdet's

constant

in

min. oer cm

-1-5

is

the

length

in

cm.

H

is

the

magnetic

field

strength

in

oersteds.

Since

we are

working

with a certain

type

of glass

both

V

and

0

are constant.

The

magnetic

field

strength

in

the

center of a

long

coil

is

:

H

=

4TTln

.,

"10-(2)

I

is

the

current

in

amp.

n

is

the

the

number of

terms

per cm.

or,

if

N

is

the

total

number of

turns,

11

Substituting

equation

2

into

1

we get:

9

=

V443lfcl

(6)

"TO

^J

The

energy

available

from

a single

layer

selonoid

is

W

=

LI2

W

is

the

energy

available

in

watt seconds.

L

is

self

inductance

in

Webers-amp-.

The

formula

for

self

inductance

of a coil

is:

L

= _un2BA

where u

is

a constant of

permability

equal

to

41Y'

x 10~9

Webers

Amp

Cm

A

is

the

cross sectional area of

the

coil =

Wr

_=Tlcl

~4

L

= TT%2d2

x IO"9

Webers

Turn2 T~

Amp

Therefore,

W

= T^2N2d2I2 _x IO"9

Watt

Seconds

21

The

energy

available

from

a capacitor

is:

W

= CE2

Watt

Seconds

2

Equating

with

the

previous equation we get:

CE2

= TTT2N2d2I2 _x 10~9

2

21

Re-arranging

for

I2

we get: I2 ₌

CE2l

zTT^d2 x IO"9

4

I

=

Ex

10

TTNd

12

Equation

3

was:

9

=

V4Tr^I

10

Substituting

for

I

we get:

9

=

4VE

_x 103

j/lOCj

d

/

Using

values:

E

=

4000

Volts

C

=

.5 x

IO"6

Farads

J

=

7.62cm

d

=

3-59cm

V

=

.071min per oersteds-cm.

OPERATING

INSTRUCTIONS

It

is

extremely

important

to

follow

these

steps

in

order

to

insure

safety.

1.

In

addition

to

the

shutter components

themselves,

(the

trigger

circuit,

high

voltage

circuit,

.nd shutter

hous

ing)

, a

two-channel

oscillescope and a variac will

be

re

quired.

2.

Connect

the

3

wire

lead

between

terminal

strips

in

trigger

circuit chassis and shutter

housing

such

that

the

terminals

"C",

"S",

and

"Q",

are one

terminal.

3.

Next,

connect one channel of

the

oscilloscope

to

the

"S"

terminal

in

either

the

shutter

housing

or

the

trigger

chassis.

Set

channel on

for

a

sensitivity

of

100

volts/

division.

4.

Connect

the

other channel

to

pin

1

of

tube

VI,

(located

next

to

pilot

lamp

on

chassis),

with a

sensitivity

of

approximately

5

volts/division.

5.

Connect

a standard

RCA

phono-tip

plug

to

the

socket

marked "TRIG" _, with

leads

sufficiently

long

to

reach

the

14

6.

Plug

in

the

triggering

circuit and

turn

the

power switch

to

"ON".

All

tubes

and pilot

lamp

should glow.

7.

Allow

one minute

for

it

to

warm up.

Then

touch

the

two

wires

leading

from

the

"TRIG"

socket.

This

should result

in

two

pulses

in

the

oscilloscope

screen,

one

indicating

the

triggering

pulse and

the

other a

delayed

pulse

to

open

the

shutter.

8.

If

no pulses are

observed,

adjust

"Sensitivity",

(see

figure

3)

until pulses are seen when contacts are shorted.

9-

Next,

the

time

between

these

two

pulses

may

be

varied

by

adjusting

"Delay

Adjust" and

"Delay

Calibration".

10.

Turn

the

circuit off and

disconnect

from

socket.

11.

Remove

oscilloscope

leads

from

pin

1, VI,

and connect

to

"Q"

terminal.

Change

the

sensitivity

to

100

volts/division

12.

Plug

the

circuit

back

in

and

turn

it

on.

The

time

delay

between

opening

and

closing

of

the

shutter

may

now

be

ad

justed

by

means of

"Quench

Adjust".

13.

Once

all

times

have

been

set,

connect

the

high

voltage

circuit

to

a variac

previously

set

to

88

VAC

output,

being

sure

to

ground

the

high

voltage

by

means of

the

three-way

15

IT

IS

VERY

IMPORTAND

NOT

TO

HAVE

MORE

THAN

88

VAC

BEING

APPLIED

TO

THE

INPUT

OF

THE

HIGH

VOLTAGE

CIRCUIT,

SINCE

ANY

HIGHER

VOLTAGE

COULD

RESULT

IN

SERIOUS

DANGER

TO

THE

EXPERI

MENTER

.

14.

Make

certain

that

polarizers are "crossed"

(scratch

on

mount aligns with scratch on

housing)

.

15.

Shutter

is

now

ready

for

use-16.

Should

adjusting

of

the

spark gaps

become

necessary,

always make sure

that

everything

is

unplugged and

that

there

is

no residual charge

left

in

the

capacitors within

16

SUMMATION

AND

RESULTS

Unfortunately,

final

testing

of

the

apparatus

failed

to

exhibit

the

desired

effect.

Difficulty

was experienced

in

attempting

to

measure

the

opening

of

the

shutter.

It

is

felt

17

DISCUSSION

It

is

felt

that

the

malfunction

lies

within

the

plexiglass

housing

and

the

poor results are

due

to

the

great magnetic

field

involved.

Perhaps

the

malfunction

may

be

eliminated

by

rewiring

the

components of

the

shutter

housing

such

that

all wires are of

minimum

length.

A

more suitable method of spark gaps should

be

devised

which would provide easier adjustments and mechanical

stability.

The

trigger

circuit seems

to

be

functioning

properly.

The

high

voltage circuit

is

charging up

the

capacitors.

Measurement

of a phototube

by

an oscilloscope was un

satisfactory

as a means of

measuring

the

shutter.

Radio

frequency

noise

from

the

high

voltage circuit was

detected

by

the

phototube and

distorted

the

desired

signal which

may

have

been

present.

The

glass-filter combination

did

not

have

the

desired

density,

when

the

magnetic

field

was off.

The

glass should

be

cut

in

half,

and a

third

polarizing

filter

cemented

between

the

two

halves

of glass.

The

first

and

last

polarized

filter

would

be

oriented such

that

their

axes of

transmission

were

parallel and perpendicular

to

the

axes of

the

center

filter.

BIBLIOGRAPHY

Specific

:

A

Rapid

Action

Shutter

with no

Moving Parts,

H.

E.

Edgerton,

C.

W.

Wyckoff,

Journal

of

Society

of

Motion

Picture

and

Television

Engineers,

Vol.

56, April,

1951

A

Microsecond

Still

Camera,

H.

E.

Edgenton,

K.

J.

Germeshausen,

Journal

of

Society

of

Motion

Picture

and

Television

Engineers,

Vol.

61,

September

1953

"Faraday

Effect",

Vol.

5,

pp.

181,

McGraw-Hill,

Encyclopedia

of

Science

and

Technology

McGraw-Hill

Book

Company,

New

York,

i960

"Magneto-Optic

Effect",

Vol.

4,

pp

476,

Encyclopedic

Dictionary

of

Physics,

Pergamon

Press,

New

York,

19

6

3

General

Handbook

of

Physics

and

Chemistry,

C.

D.

Hodgmaned,

35th

edition.

Chemical

Rubber

Publishing Co., Cleveland,

Ohio,

1953

The

Radio

Ametures'

Handbook,

American

Radio

Relay

League,

West

Hartford,

Conn.,

I96I

Geometrical

and

Physical

Optics,

R.

S.

Longhurst,

J.

Wiley,

and

Sons,

New

York,

19

6 8

University

Physics,

R.

W.

Sears,

M.

W.

Zemansky,