Lasers, Uv, Microwaves

Question 1

Describe the characteristics of laser light

Answer 1

• Monochromatic (one frequency of wavelengths contained)
• Coherent (all light is in phase)
• Directional (Laser light emitted is highly directional and slow to diverge)
• Intense (Laser beams have a high intensity)

Question 2

4 affects that happen due to lasers that may be used for treatment

Answer 2

-Photochemical (UV and blue light. Low irradiances that don’t cause temperature changes. e.g. skin tanning, psoriasis treatment, cataracts)

• Thermal (Above a critical temperature proteins will become denatured and thermally induced damage occurs)
• Photoablation (UV photons, Heated material is rapidly removed. Application is vision correction.
• Thermomechanical (When tissue is heated rapidly. Rapid thermal expansion and vaporisation of liquid leads to mechanical shockwaves. Cells rupture. e.g. kidney stone removal, fibrous tissue after cataract surgery removal.)

Question 3

What is the range of non-ionising wavelengths that are classed as a retinal hazard.

Answer 3

400 - 1400nm. young eyes 380nm due to higher transmittance. Retinal damage is permanent

Question 4

What are the 3 types of laser interactions

Answer 4

Scattering (short wavelength = more scattering = less penetration depth. Occurs due to structures that have a similar size to it’s wavelenght of slightly larger i.e. collagne fibres.)

Transmission - If no chromophore all photons will pass through the tissue without any effect.

Reflection - Occurs at all interfaces. To reduce reflection have a firm contact with skin and a light guid such as a jelly.