Lasers Flashcards
What does LASER stand for?
Light Amplification of Stimulated Emission of Radiation
Whats is spontaneous emission?
When a photon is applied to an atom the electrons in the orbital will gain energy and move to a high energy orbital, it is in its excited state.
As the electron moves back to its original orbital (moves back to the ground state) it will emit a photon. This is spontaneous emission.
If the photon is in the visible light spectrum then this is known as fluorescence.
What is stimulated emission?
Energised electrons act as energy sources for neighbouring atoms to achieve the same energised state.
When a photon of energy from a stimulated atom interacts with an identically stimulated atom, it will move to an even higher energy state, known as stimulated emission.
When it relaxes, it will release 2 identical photons of light that are in phase with each other.
Population inversion describes when a sufficient number of atoms are energised and there is a majority of atoms with electrons in the higher energy state.
LASER light is created from stimulated emission.
What are the 3 properties of LASER light?
- Monochromatic: One specific wavelength
- Coherent: All waves are in phase with each other*
- Collimated: Highly directional
- If two waves coincide with peaks and troughs matching they are said to be in phase
Describe how a LASER works?
There is a lasing medium (all of the same atom) it can be a gas, liquid or solid.
The lasing medium is pumped with energy usually in the form of light or electricity. This allows stimulated emission.
The lasing medium housing has mirrors at each end so that photons that are released reflect back and further excite the lasing medium until population inversion occurs.
There is a small opening at one end which will allow light energy once intense enough to leak through (giving you your laser beam).
Currently lasers emit infra-red, visible light and UV light.
There are hypothetical gamma ray lasers but they have not been developed.
What are the clinical applications of infrared lasers?
Infrared (IR): induces molecular vibration leading to heating effects of the tissue.
-CO2 LASER: 10,600nm: absorbed by tissue water within 1mm of the tissue surface allowing bloodless cutting and vaporisation.
Nd:YAG LASER: 1064nm: increased penetration to 3-5mm depth absorbed by Hb, melanin and water. Used in dermatology.
Generally speaking light from the far end of the infrared spectrum and ultraviolet spectrum has poor penetration. And light from the lower end of the IR spectrum has greater penetration.
What are visible light lasers used for?
Argon LASER: 488-515nm blue-green: Penetrates to 2mm and absorbed by tissues of complimentary colour i.e. Hb. Therefore, can be used for blood coagulation whilst avoiding transparent tissues i.e. retinal photocoagulation.
What are the different classes of energy in Lasers?
Class 1
Cannot emit radiation at any known hazard levels (for the eye); this means very low power output.
Class 2
Low-power visible lasers, at a radiant power <1 mW
Class 3
Intermediate and moderate power lasers, and are hazardous only if the beam itself is directly viewed;
-Class 3a devices can have a power output up to 5 mW through a sufficiently divergent beam and the eye may be protected by the blink reflex.
-Class 3b devices have power output up to 500 mW, when direct viewing may be hazardous to the eye
Class 4
High power lasers (>500 mW, continuous beam), which are very hazardous to view and are a hazard to skin as well.
Most medical lasers are class 4
What is Q switching?
Higher output lasers result in cellular fluid vaporisation and destruction. Therefore, LASERS are pulsed to allow heat dissipation and reduce destruction to neighbouring tissues – this is known as a Q-switching technique.
What safety mechanisms are needed when using class 4 lasers?
Appropriate training
Safety goggles that are specific to the wavelength of light being used
Environmental factors i.e. locked and screened doors and windows with signs.
Note lasers are non-divergent in nature (unlike XR beams) – distance does not add any measure of safety.
When is there a particular risk with flammability and the use of Lasers, how is this risk mitigated?
During airway surgery when lasers are used.
Flammability is an issue with airway surgery with high FiO2 or use of N2O. This can also be an issue if lasers are directed to the drapes.
Modern volatile agents are non-flammable. Reduced O2 concentration in the vicinity of the beam will reduce this risk – maximum suggested at FiO2 0.25.
For airway surgery specific LASER tracheal tubes should be used and plastic tubes avoided.
The cuffs of ETT are usually doubled and both ETT and LMA cuffs are filled with saline rather than air.
What is the significance of reflected Lasers?
They are almost as powerful as the incident beam so non-reflective i.e. matt black instruments should be used. Neighbouring tissues should be protected with wet swabs.
