Wavelengths and Absorption
Laser light’s monchromaticity is responsible for its selective effect on biologic tissue. Whenever light hits tissue, it can be transmitted, scattered, reflected, or absorbed, depending on the type of tissue and the wavelength (color) of the light.
However, light absorption must take place for there to be any biologic effect, and a given wavelength of light may be strongly absorbed by one type of tissue, and be transmitted or scattered by another.
Infrared light is absorbed primarily by water, while visible and ultraviolet light are absorbed mainly by hemoglobin and melanin, respectively.
As the wavelength decreases toward the blue-violet, and ultraviolet, scatter, which limits the depth that light may penetrate into tissue, becomes more significant.
As the wavelength decreases toward the blue-violet, and ultraviolet, scatter, which limits the depth that light may penetrate into tissue, becomes more significant.
When light is absorbed, it delivers energy to tissue, and the tissue’s reaction depends on the intensity and exposure time of the light.
Each type of tissue has its specific absorption characteristics depending on its specific components (i.e., skin is composed of cells, hair follicles, pigment, blood vessels, sweat glands, etc.)
The main absorbing components, or chromophores, of tissue are:
- Hemoglobin in blood
- Melanin in skin, hair, moles, etc.
- Water (present in all biologic tissue)
- Protein or “Scatter” (covalent bonds present in tissue)
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