- The invention of the LASER is one
of the most significant developments in science and engineering
- To enable us to understand and
appreciate the operation of this unique device requires
- an understanding of the behaviour
and the properties of light itself
- Light is the medium by which we carry
information through an optical system
- our immediate task is to ask
ourselves
- what is light?
- what are its origins?
- Light is not the easiest of natural
phenomena to describe
- for many centuries, scientists have
debated, and argued over, the nature of light
- we will not take part in this debate
but will try to present a description of light which will satisfy
our working needs
- To understand the operation of the LASER
and other light sources, we need to appreciate the unique character of
the light emitted from gases and solids
- all radiating bodies when viewed by
the naked eye appear to possess a characteristic colour:
- sunlight is white
- a piece of hot iron may be
orange-red
- a sodium street lamp is yellow
- If the light from any of these
sources is passed through a prism it spreads out in a series of
component colours known as a SPECTRUM
- sunlight appears as a continuous
band of colours ranging from red through to violet
- a piece of iron also shows a
continuum from dull red to orange
- a sodium lamp displays a series
of bright, narrow lines
- whether the spectral distribution is
a CONTINUOUS SPECTRUM or in DISCRETE SPECTRAL LINES depends
on
- the nature of the source
- the temperature of the source
- To completely describe the properties of
light requires us to adopt two different models of behaviour:
- the ELECTROMAGNETIC WAVE
model
- the PHOTON model
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