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2.1.2 Scattering, Done by: Allen Paul David & Siti Syafirah - Coggle…
2.1.2 Scattering
2.1.1 Absorption
Absorption of a photon takes place only when its energy, E=hv, corresponds to the energy difference between such quantized states.
Absorption of a photon by a chromophore causes:
- quantized change in the distance between charges (electron transition, ultraviolet or visible spectrum
- quantized change of vibrational modes of the molecule (vibration transition, near infrared [NIR]
In the NIR and mid-infrared (MIR) region, tissue absorption is dominated by water absorption, with the maximum at 3 µm.
Vibration transitions of a water molecule with its absorption bands 
Scheme of electronic excitation after photon absorption
Introduction
- Determines the volume distribution of light intensity in the tissue.
- The primary step of tissue interaction, which is followed by absorption and heat generation.
- Scattering structure of the tissue can be macroscopic like muscle fibres, skin layers or dentin tubules (microscopic structure)
- Scattering in tissue an come in the form or Rayleigh or Mie scattering.
Application
- Possibility to measure the light distribution inside the tissue by introducing a miniaturized probe of 100-um diameter. Via a hollow needle of the syringe.
- Increased fluency rate in the outcome since scattering photons will overlap with the incident photons.
- Penetrating depth will also be doubled with increased diameter from 1mm to 5mm. Useful in dermatological application.
- The depth of penetration of laser light into tissue is greatest in the wavelength range of 700 - 900nm. Blood, water and melanin are the main absorbing components in the tissue.
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