Medical lasers are tools that deliver concentrated light energy to a very small area of the body. Doctors use them to cut, seal, reshape, or remove tissue with high precision. The effect depends on the laser wavelength, the beam power, the exposure time, and the type of tissue being treated.
Understanding how these factors work helps explain why one laser can seal blood vessels while another can reshape the cornea.
Key Facts
- Photon energy is E = hf = hc/λ, so shorter wavelengths have higher photon energy.
- Laser power is P = E/t, where power is energy delivered per second.
- Irradiance is intensity over area: I = P/A, so focusing a beam into a smaller spot increases its effect.
- Fluence is energy per area: F = E/A, which helps predict heating or tissue change.
- Different tissues absorb different wavelengths because water, hemoglobin, and melanin absorb light differently.
- Main laser tissue effects include photothermal heating, photoablation, photochemical reactions, and photomechanical disruption.
Vocabulary
- Laser
- A laser is a device that produces a narrow, organized beam of light with one main wavelength.
- Wavelength
- Wavelength is the distance between repeating peaks of a light wave and helps determine how strongly tissue absorbs the light.
- Irradiance
- Irradiance is the laser power delivered per unit area, usually measured in watts per square centimeter.
- Chromophore
- A chromophore is a molecule or material in tissue, such as water, hemoglobin, or melanin, that absorbs specific wavelengths of light.
- Photoablation
- Photoablation is the removal of tissue by laser energy that breaks molecular bonds or rapidly vaporizes material at the surface.
Common Mistakes to Avoid
- Treating all lasers as the same is wrong because wavelength controls which tissue components absorb the energy.
- Thinking higher power is always better is wrong because excess power can spread heat and damage nearby healthy tissue.
- Ignoring spot size is wrong because the same power focused into a smaller area produces much higher irradiance.
- Confusing reflection with absorption is wrong because only absorbed laser energy can heat, cut, or chemically change tissue.
Practice Questions
- 1 A medical laser delivers 6 J of energy in 2 s. What is its power in watts?
- 2 A 4 W laser is focused onto a spot with an area of 0.02 cm². What is the irradiance in W/cm²?
- 3 A surgeon wants to seal tiny blood vessels without cutting deeply into nearby tissue. Explain why choosing a wavelength strongly absorbed by hemoglobin and using controlled power would help.