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Lasers in Medicine: Healing with Light
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
The penetration depth is determined by the extinction coefficient, which characterizes the degree of absorption by individual molecules and concentration of the absorbing molecules by the equation: L=1/(εc) where ε is the extinction coefficient and c is concentration. The value of the extinction coefficient depends on the wavelength of light being absorbed. This means that the more absorbers present along a given pathway, the shorter the distance light travels before being absorbed – higher concentrations lead to shorter penetration depths. Similarly, the penetration depth is shorter if the extinction coefficient of the material is greater; both depend on wavelength. For example, for green light, blood-filled tissue absorbs light in a shorter distance than tissue containing little blood. Similarly, the lens of the eye has a long penetration depth for visible light. By contrast, visible wavelengths have short penetration depths in the retina, which has a high concentration of strongly absorbing visual pigments.
Biomedical Applications in Probing Deep Tissue Using Mid-Infrared Supercontinuum Optical Biopsy
Published in Lingyan Shi, Robert R. Alfano, Deep Imaging in Tissue and Biomedical Materials, 2017
In the MIR range, molecular species exhibit fundamental absorption bands with large extinction coefficients thus MIR spectroscopy potentially provides extremely sensitive chemical analysis. A molar extinction coefficient (or molar absorptivity coefficient) is defined by the Beer-Lambert law and is a measure of the relative light absorption of a particular vibrational mode of a molecular species normalized to the molar concentration of the absorbing species. Knowledge of the molar extinction coefficient allows quantification of the amount of the molecular species present. The response to MIR spectroscopy is collected as a spectrum, of the material concerned, which is a plot of intensity of MIR radiation versus wavelength and shows the uptake of radiation intensity at particular wavelengths due to vibrational absorption of the material which is characteristic of the molecular structure of the material.
Materials for Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
In contrast to the fluorophores, the size of the QD determines its peak PL wavelength. With decreasing size of the QD, the peak PL wavelength changes from red to blue. The absorbance onset and emission maximum shift to higher energy. A QD absorbs light at any wavelength smaller than its peak PL wavelength. The excitation tracks the absorbance, resulting in a tunable fluorophore that can be excited efficiently at any wavelength shorter than the emission peak, yet will emit with the same characteristic narrow, symmetric spectrum regardless of the excitation wavelength. This enables the simultaneous excitation of many QDs having different emission wavelengths by a single wavelength source in the blue or ultraviolet region, creating a Stokes shift, ~100−300 nm, much larger than for fluorophores. Variation of the material used for the nanocrystal and also of the size of the nanocrystal affords a spectral range of 400 nm−2 μm in the peak emission, with typical emission widths of 20−30 nm (full width at half-maximum [FWHM]) in the visible region of the spectrum and large extinction coefficients in the visible and ultraviolet range (~105 M−1 cm−1). The full width at half maximum) is a parameter commonly used to describe the width of a “bump” on a curve or function; it is given by the distance between points on the curve at which the function reaches half its maximum value. The extinction coefficient is a parameter that defines how strongly a substance absorbs light at a given wavelength per mass unit. Many sizes of nanocrystals may therefore be excited with a single wavelength of light, resulting in many emission colors that may be detected simultaneously. QDs combine a broad excitation spectrum with a narrow emission spectrum.
Synthesis and crystal growth of cadmium naphthoate crystal for second order non-linear optics and cytotoxic activity
Published in Journal of Dispersion Science and Technology, 2022
Natarajan Arunadevi, Ponnusamy Kanchana, Venkatesan Hemapriya, Shanmuga Sundari Sankaran, Mehala Mayilsamy, Prabha Devi Balakrishnan, Ill-Min Chung, Prabakaran Mayakrishnan
Extinction coefficient is the measurement of the fraction of light lost because of scattering and absorption per unit distance of the material and it probably depends on the chemical composition and structure of the material. Extinction coefficient (k) is measured using the following relation, where, α - absorption coefficient and λ - wavelength. From Figure 10e, it is clear that the extinction coefficient increases as photon energy increases.[60]
Physical properties of molybdenum monoboride: Ab-initio study
Published in Philosophical Magazine, 2018
Priyanka Rajpoot, Anugya Rastogi, U. P. Verma
The extinction coefficient is the imaginary part of the index of refraction, which relates to light absorption. Figure 6(d) shows the spectra of extinction coefficient k(ω), which possess many peaks in the energy range 1.18–10 eV and highest peak for kxx(ω), kyy(ω)and kzz(ω) appear at 1.59, 1.18 and 1.26 eV, respectively. Beyond 13 eV, k(ω) decreases with increase in energy and attains zero value near 28 eV.
Study of C.I. Reactive Yellow 145, C.I. Reactive Red 238, and C.I. Reactive Blue 235 dyestuffs in order to use them in color formulation. Part 1: characterization and compatibility
Published in The Journal of The Textile Institute, 2019
Sabrine Chaouch, Ali Moussa, Imed Ben Marzoug, Neji Ladhari
The molar absorptivity, also called molar extinction coefficient, characterizes the capability of a solution to absorb light. It is a measure of how strongly a chemical species or substance absorbs light at a particular wavelength; so it is an intrinsic property of chemical species that is dependent upon their chemical composition and structure (McNaught & Wilkinson, 1997).