Fundamentals of Light Sources
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 optical fiber
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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 optical fiber lasers. This chapter first 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 configurations, 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 category 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 and fluids (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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4 Fundamentals of Light Sources
An important factor to keep in mind is that biological tissue has a multilayered characteristic from both compositional and functional viewpoints. Specific biological processes and diseases occur at different levels within this multilayered structure. Thus when selecting an optical source, it is necessary to ensure that the specific wavelength of the light that is aimed at the targeted biological process or disease can penetrate the tissue down to the desired layer. The medical field also uses many types of surgical lights and a variety of lamps for illumination and visual diagnostic purposes in operating ro
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