Diffraction Mosaic
Experiment Guide
Experiments include:
Knife Edge
Single-Slit
Double-Slit
Multiple-Slit or Array
Model Number:
IF 508
I
ndustrIal
F
Iber
O
ptIcs
*
Copyright © 2008
Previous printings 2006. 2000
by Industrial Fiber Optics, Inc.
Revision - C
Printed in the United States of America
* * *
All rights reserved. No part of this publication may be reproduced,
stored in a retrieval system, or transmitted in any form or by any means
(electronic, mechanical, photocopying, recording, or otherwise)
without prior written permission from Industrial Fiber Optics.
* * * * *
IntroductIon
To a casual observer, light in the world around us seems to travel in a
straight line. The appearance of shadows and reflections in mirrors seems to
support this conclusion. The behavior of light in these instances can be explained
with ordinary geometry. Light is either reflected, absorbed, scattered, or some
combination of the three, but the path it takes can be traced using straight lines
and angles.
In reality, light also has properties normally associated with the motion of
waves observed in nature, such as ripples on a lake or pond. Occasionally we
see evidence of light’s wave properties, such as the colors on a soap bubble or
a thin layer of oil floating on water. The effect of polarized sunglasses to reduce
the glare from water, or the colors we see in a rainbow are further evidence of the
wave characteristics of light.
In this experiment guide we will demonstrate the wave properties of light
using a laser, some ordinary household items and a diffraction mosaic. We will
start with a basic demonstration of diffraction (light bending around a corner)
using a laser and knife (razor) blade edge. Our experiments will then progress to
more dramatic visual effects that result from wave interference (light waves being
added and subtracted) with single-slit, double-slit and multiple-slit apertures.
The wave properties of light, including the phenomenon of interference,
were proven experimentally in 1801 by an English physicist and physician named
Thomas Young (1773-1829). Young assumed that light traveled in a way similar
to sound waves and that different colors were caused by changes in wavelength.
In Young’s experiment, light was passed through a series of narrow slits and
projected onto a screen. The result was a pattern of light and dark regions known
as diffraction fringes. These fringes were caused by the additive and subtractive
effects of interference that could only occur if light was traveling as a wave. His
findings eventually were confirmed by French engineer Augustin Fresnel — but
initially were challenged by contemporary scientists who preferred [the more pop-
ular] Isaac Newton’s theory that light was “corpuscular” or particle-like in nature.
The diffraction mosaic pictured on the front cover of this manual is a mount-
ed photographic film containing precisely etched lines or slots. These are ar-
ranged as a set of four double-slit lines and three multiple-slit arrays. The mosaic
will greatly aid in demonstrating the wave properties of light by reducing the effort
and errors for experimental setup. The visual results will be more impressive, too.
Using Industrial Fiber Optics’ Diffraction Mosaic and experiment guide you will
learn about the hidden effects in the light around us.
–1–
KNIFE EDGE DIFFractIoN
When a beam of light is partially blocked by some object,
a shadow is created. Under special circumstances it can be
shown that an obstruction actually causes diffractive effects
related to the wave properties of light. Figure 1 shows what
occurs when an obstruction with an opening in it is placed
in the path of a wave front. When the wave passes through
the opening it diffracts or behaves as if a new source of
waves (a secondary wavefront) was created at the obstruc-
Figure 1.
tion. Notice how the waves spread out beyond the actual size
Waves diffracting as they
pass through an aperture.
of the opening.
The following experiment will demonstrate diffraction of a
light beam by showing how light can bend around a corner. Subsequent procedures will
produce increasingly dramatic effects from light’s wave properties.
Equipment Needed:
•
•
Helium neon laser with 632.8 nm emission wavelength*
Single-edge razor blade
* Other helium neon lasing wavelengths and other visible gas lasers will work also, but the
examples used in this manual assume the use of the 632.8 nm helium neon laser. (Diode
lasers will also work for this experiment, but the interference fringes will not be as sharp.)
The procedures in this manual are written for use with Industrial Fiber Optics helium
neon lasers. You may need to adjust the steps slightly to accommodate other manufactur-
ers’ lasers.
Procedure:
1.
2.
Review the laser safety rules on the back cover of this manual.
Find a table approximately 600 × 900 cm (2 × 3 feet) or larger in size
from which the laser can be pointed toward a wall or other dull reflecting
surface. The distance from the laser to the surface should be approximately
three meters (10 feet).
Push the laser beam stop handle downward to its closed position and make
sure its ON/OFF switch (SW) is in its OFF position. (The push button
should be in its extended position.)
Plug the 110 VAC-to-DC power adapter (provided with the laser) into an
AC wall outlet.
Insert the cord from the power adapter into the power jack (PWR) located
on the rear of the laser.
–2–
3.
4.
5.
6.
7.
8.
9.
Depress the ON/OFF switch (SW) on the control panel of the laser until it
clicks into the ON position. (The switch should be slightly depressed.)
The pilot light (green LED) just to the right of the ON/OFF switch should
now be lit, showing that the laser is on.
Push the laser’s beam stop handle upward, to its open position.
Observe the red beam striking
the wall, or other surface, in
the direction which the laser is
pointed.
Tape the single-edge razor to a
book or wood block so the sharp
edge is perpendicular to the
tabletop. Make certain the razor
is high enough to block the laser
beam if you slide the razor’s edge
into the path of the beam. The
sharp edge of the blade must
extend past the edge of the book
or block.
Dim the room lights and slide the razor
blade until its edge almost completely
blocks the beam.
10.
11.
Figure 2.
Single-edge razor blade and its
relationship to the laser.
12.
At this point (you must look very carefully) you should see a streak of light
on the wall that is perpendicular to the vertical edge of the razor blade. If
you position the razor blade carefully you will see a pattern of bright and
dark areas in the light streak as shown in Figure 3.
Turn on the room lights, then push the beam stop handle on the laser
down to its closed position. Turn off the laser and put away all the materi-
als used in this experiment.
13.
results:
When you obstructed the laser beam with the
sharp edge of the razor, you created a second-
ary wavefront at the edge of the razor. The
light streak you observed was the result of light
waves spreading from the second wavefront
created at the razor’s edge. The light and dark
areas in the streak occur where waves from the
unobstructed portion of the original beam inter-
fere with those from the secondary wavefront.
Figure 3.
Laser beam pattern from
single-edge razor edge.
– 3 –
工作这点儿事
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
