Nature and Properties of Light

Nature and Properties
of Light
Linda J. Vandergriff
Director of Photonics System Engineering
Science Applications International Corporation
McLean, Virginia
Light plays a vital role in our daily lives. It is used in compact disc (CD) players, in which a
laser reflecting off a CD transforms the returning signal into music. It is used in grocery store
checkout lines, where laser beams read bar codes for prices. It is used by laser printers to record
images on paper. It is used in digital cameras that capture our world and allow pictures to be
displayed on the Internet. It is the basis of the technology that allows computers and telephones
to be connected to one another over fiber-optic cables. And light is used in medicine, to produce
images used in hospitals and in lasers that perform eye surgery.
The generation, transport, manipulation, detection, and use of light are at the heart of photonics.
Photonics is a critical part of the future and a growing career field. In 1997 it was a $50 billion
market with a projected growth of 10 to 20 percent over the next decade. Photonics technicians
and engineers must master new concepts, learn new techniques, and develop new skills. To
work in photonics it is necessary to have a basic understanding of the nature of light and its
properties.
Prerequisites
This module requires a basic understanding of high school algebra, trigonometry, general
scientific nomenclature, the scientific process, units conversions, and basic concepts in
elementary physics and chemistry.
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F U N D AM E N T AL S O F P H O T O N I C S
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Objectives
When you finish this module you will be able to:
• Describe the wide variety of opportunities for photonics technicians.
• Define and use basic radiometric units.
• Define the following properties of light:
? Speed
? Frequency
? Wavelength
? Energy
• Describe the dual nature of light, as a continuous wave and a discrete particle (photon),
and give examples of light exhibiting both natures.
• Describe the six properties of electromagnetic waves and give everyday examples.
• Explain the mechanism that causes light to be polarized, explain the use of polarizing
material, and give an example of the use of polarizers.
• Describe Huygens’ principle and the superposition principle.
• Define the terms reflection, refraction, and index of refraction and explain how they are
related.
• Explain diffraction and interference in terms of Huygens’ principle.
• List the three types of emission and identify the material properties that control the
emission type.
• Describe in a short paragraph the electromagnetic spectrum and sketch a diagram of the
key optical regions and uses.
• Give a basic explanation of atoms and molecules and their ability to absorb, store, and
emit quanta of energy.
• Define the primary equations describing the relationships between temperature of,
wavelength of, and energy emitted by a blackbody and a graybody.
• Describe the mechanisms that affect light propagating in a medium and its transmission.
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N AT U R E A N D PROP E R T I E S O F L I G H T
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True Life Scenario
Holly works as a photonics assembly technician. The factory where she is
employed creates laser diode assemblies for a variety of commercial uses. As
an assembly technician, she creates and aligns laser diode components and
ensures that the bonded products meet the tight quality standard she and her
company require of all their products.
At the beginning of the shift, Holly gets her
assignment for the production run. She
prepares for entering the clean room where
the work will take place. Then, after entering,
she logs on at her assembly station. She
selects the correct workspace file for the
devices to be manufactured during that shift.
The workspace file selection is based on
wavelength, other optical properties, and
pass/fail criteria set for this particular device.
With the components provided, Holly first
sets up the lateral shearing interferometer
and the microlens/laser diode product. Then
she collimates and directs the laser diode
beam into the beam analysis tool for testing.
Figure 1-1 Photonics assembly
technician assembling LEDs1
After that she reviews the results on the computer monitor and adjusts the
alignment until the device is acceptable. Finally, she bonds the microlens and
laser diode and stores the final measurements to a log file on the network
server. These measurements, along with those of the other devices created
during this production run, will serve as a statistical base for evaluation of the
production process and the product quality.
Holly will create a batch of microlens/laser diode pairs during her shift. Depending
on the order and application, this run may require days or weeks. Then a
new product will be designed for production, and Holly and her counterparts on
the production floor will create it. This will require an evolving understanding of
light and its uses to allow flexibility in the manufacturing process and keep Holly
and her company competitive in the growing marketplace.
Opening Demonstration
Note: The interactive exercise that follows is to be used as a short introduction to the wide
range of photonics applications. It is intended to stimulate interest in the study of photonics.
Instructions: Create two or three groups. Have each group, with notes and manuals closed and
without repeating, name a use of light technology. When no one in a group can think of a use
that has not already been added to the list, that group drops out. Compare the groups’ lists with
the one following. Did the groups miss any areas? Are there any areas that should be on the
following list but are not?
1 Source: Laser Focus World, May 1999, 291. Reprinted by permission.
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F U N D AM