Chapter 4
Fundamentals of Light Sources
Abstract A broad selection of light sources is available for the biophotonics UV,
visible, or infrared regions. These sources include arc lamps, light emitting diodes,
laser diodes, superluminescent diodes, and various types of gas, solid-state, and
opticalfiber lasers. This chapterfirst defines terminology used in radiometry, which
deals with the measurement of optical radiation. Understanding this terminology is
important when determining and specifying the degrees of interaction of light with
tissue. Next the characteristics of optical sources for biophotonics are described.
This includes the spectrum over which the source emits, the emitted power levels as
a function of wavelength, the optical power per unit solid angle emitted in a given
direction, the light polarization, and the coherence properties of the emission. In
addition, depending on the operating principles of the light source, it can emit light
in either a continuous mode or a pulsed mode.
Many categories of light sources with diverse sizes, shapes, operational configu-
rations, light output powers, and emitting in either a continuous or a pulsed mode
are used in biophotonics. These sources can be selected for emissions with different
spectral widths in the UV, visible, or infrared regions. Each light source cate-
gory has certain advantages and limitations for specific life sciences and medical
research, diagnostic, imaging, therapeutic, or health-status monitoring applications.
The characteristics of the optical radiation emitted by any particular light source
category can vary widely depending on the physics of the photon emission process
and on the source construction and its material. The decision of which optical
source to use for a given application depends on the characteristics of the optical
radiation that is emitted by the source and the way this radiation interacts with the
specific biological substance or tissue being irradiated. That is, as Chap. 6
describes, the absorption and scattering characteristics of light in biological tissues
andfluids (e.g., skin, brain matter, bone, blood vessels, and eye-related tissue) are
dependent on the wavelength region, and the interactions of light with healthy or
diseased cells can vary significantly.
©Springer Science+Business Media Singapore 2016
G. Keiser,Biophotonics, Graduate Texts in Physics,
DOI 10.1007/978-981-10-0945-7_4
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