eLFH - Lasers Flashcards
LASER acronym
Light
Amplification of
Stimulated
Emission of
Radiation
Laser beam definition
Intense, monochromatic, non-divergent, narrow beam of light producing very large amount of energy distributed over a small area
Fluorescence definition
Spontaneous emission of light energy from atoms of the same species in the material when atom goes from excited state to ground state
(electrons move from higher energy orbitals to lower energy orbitals)
Stimulated emission
Energised electrons act as energy sources for neighbouring atoms to achieve the same energised state
When majority of atoms in medium are energised to ecited state then ‘population inversion’ has occurred
If an already excited atom is stimulated by photon, then it releases two identical photons
Features of LASER light created by stimulated emission
Monochromatic - one specific wavelength
Coherent - all waves are in phase
Highly directional - collimated
How does Laser work
Lasing medium - gives LASER its characteristic wavelength or colour
Lasing medium pumped with energy to to get atoms to excited state
Mirror at each end to reflect photons back and forth to continue stimulated emission of lasing medium
One of the mirrors not completely silvered so once light energy becomes adequately intense, light beam can leak through it
Examples of energy that is pumped into lasing medium
High intensity flashes of light or electrical discharges
Examples of lasing mediums
Solid - ruby, Nd:YAG
Gas - CO2, Argon-ion gas
Liquid - dyes
Semiconductors
Nd:YAG
Neodymium:Yttrium-Aluminium Garnet
Solid lasing medium
Wavelength of ruby laser
694.3 nm
Wavelength of CO2 laser
10,600 nm
Physical interactions that can be caused by lasers depending on the lasing medium used
Optical
Thermodynamic
Photochemical
Factors which impact the choice of laser / lasing medium used for each clinical use
Tissue absorption and penetration
Availability of laser device of the correct wavelength
Safety with surrounding equipment / anatomy
Physical interactions induced by infrared lasers
Infrared energy induces molecular vibration causing heating effects of tissue (thermodynamic interactions)
Physical interactions induced by visible light lasers
Photochemical interactions by molecular bond dissociation
Can cause skin burns
Use of CO2 laser
Surgical use e.g. gynae
Argon-ion gas laser use
Ophthalmology
Nd:YAG laser use
Dermatology
Q switching
Pulsed emissions to allow dissipation of heat between short Laser bursts
Aims to reduce damage to neighbouring tissues
Used in Ophthalmology
What determines penetration of laser beam
Wavelength
Longer wavelength absorbed more by tissue so has lower penetration (UV and infrared spectrum)
CO2 Laser wavelength, penetration and main use in surgery
10,600 nm (far IR)
1 mm penetration
Used as bloodless cutter and vaporiser
Argon Laser wavelength, penetration and main use in surgery
488 - 515 nm (blue-green)
2 mm penetration and absorbed by tissues of complementary colour (e.g. Hb)
Used to coagulate blood in vessels and avoids damage to transparent tissues e.g. retina
Nd:YAG Laser wavelength and penetration
1064 nm (IR)
3 - 5 mm penetration
Absorbed by Hb, melanin and water
Risks associated with LASER use
Eye damage - beams are non-divergent so distance does not add safety and reflected beams can still cause damage
Flammability - gases, drapes, ETT / cuff
Safety mechanisms when using LASER in theatre
Safety goggles for all staff + patient specific to type of laser in use
O2 concentration as low as possible in vicinity - max 25%
Matt black instruments to minimise reflection
Non-flammable ETT
Fill cuff with saline not air
Classification of LASERs
4 groups according to energy output
Class 1
Class 2
Class 3
Class 4
Class 1 LASERs
Cannot emit radiation at any known hazard levels for the eye
Very low power output
Class 2 LASERs
Low power visible lasers
Radiant power less than or equal to 1 mW
Class 3 LASERs
Intermediate and moderate power lasers
hazardous only if the beam is directly viewed
Class 3a have power output up to 5 mW
Class 3b have power output up to 500 mW
Class 4 LASERs
High power lasers >500 mW
Continuous beam
Very hazardous to view and hazard to skin too
Most common class of LASER used clinically
Class 4
