Lasers
Light Amplification by Stimulated Emission of Radiation
High voltage directed into a lasing medium.
Current flow excites atoms in the medium (electrons at a higher energy level).
When return to ground state emit a photon.
If this encounters another excited atom then this will release a photon parallel and in phase with the first.
So reflecting photons back and forth between mirrors generates a chain reaction which produces an intense beam of light which is:
- Uniform wavelength
- In phase
- Non-divergent
Liquid
Solid – Nd:YAG
Each has a characteristic wavelength which will determine its absorption by various substances.
CO2 produces IR light which is absorbed by water which is vapourised. Therefore good for cutting and coagulation with minimal penetration.
Argon absorbed by red tissues so good for retinal surgery.
Nd:YAG has deep penetration.
Safety
Theatre
Sign on door
Non reflective materials
Staff - eyes
Protective goggles
Warn when laser to be fired
Patient (burns) – most risk in ENT surgery
Laser resistant ETT (metal coated) – PVC ETT will ignite in seconds
Saline in cuff
Wet swabs around lesion being treated
Avoid N2O (supports combustion)
Minimise O2 (25%)