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Optofluidic Dye Lasers 243

completeness we begin with a brief and pedestrian introduction to
laser physics and dye lasers.

10-2 Laser Basics
Today, lasers are used in a large variety of daily life applications
including telecommunication, audio and video disk players, machin-
ing, surgery, dentistry, positioning, and sensing. These applications
rely on the key properties of laser light: monochromaticity and coher-
ence, as opposed to other light sources such as Edison’s glow bulb
and light-emitting diodes (LED) which emit noncoherent photons in
a wide band of frequencies. The word “laser” is an acronym for light
amplification by stimulated emission of radiation.
The laser can simply be described as a feedback coupled
amplifier for photons, as illustrated in Fig. 10-2a, which to first order
oscillates at a resonance frequency determined by the spectral prop-
erties of the feedback and gain medium. This is quite analogous to

Feedback
I out
Output, I th
Input, I 0 Output, I out
Gain, A
(a)
Input, I 0
(c)

f
Output, I out 0
Gain medium I out
Output,

Mirror Mirror
R~100% Input, I 0 R < 100% Output frequency, f
(b) T > 0% (d)
FIGURE 10-2 The laser can be described as a feedback coupled amplifier for
photons, see panel (a). The amplification provided by a gain medium inserted in an
optical resonator, for example, formed by two mirrors, see panel (b). Panel (c)
outlines the input-output characteristics of a laser (solid line) with a characteristic
threshold, I for onset of lasing, opposed to the behavior in the absence of lasing,
th
for example, florescence (dotted line). Panel (d) shows the corresponding
characteristic narrow-line emission spectrum from a laser (solid line), compared to
the broad emission spectrum of traditional light source.