eLFH - Lasers

Question 1

LASER acronym

Answer 1

Light
Amplification of
Stimulated
Emission of
Radiation

Question 2

Laser beam definition

Answer 2

Intense, monochromatic, non-divergent, narrow beam of light producing very large amount of energy distributed over a small area

Question 3

Fluorescence definition

Answer 3

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)

Question 4

Stimulated emission

Answer 4

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

Question 5

Features of LASER light created by stimulated emission

Answer 5

Monochromatic - one specific wavelength

Coherent - all waves are in phase

Highly directional - collimated

Question 6

How does Laser work

Answer 6

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

Question 7

Examples of energy that is pumped into lasing medium

Answer 7

High intensity flashes of light or electrical discharges

Question 8

Examples of lasing mediums

Answer 8

Solid - ruby, Nd:YAG

Gas - CO2, Argon-ion gas

Liquid - dyes

Semiconductors

Question 9

Nd:YAG

Answer 9

Neodymium:Yttrium-Aluminium Garnet

Solid lasing medium

Question 10

Wavelength of ruby laser

Answer 10

694.3 nm

Question 11

Wavelength of CO2 laser

Answer 11

10,600 nm

Question 12

Physical interactions that can be caused by lasers depending on the lasing medium used

Answer 12

Optical

Thermodynamic

Photochemical

Question 13

Factors which impact the choice of laser / lasing medium used for each clinical use

Answer 13

Tissue absorption and penetration

Availability of laser device of the correct wavelength

Safety with surrounding equipment / anatomy

Question 14

Physical interactions induced by infrared lasers

Answer 14

Infrared energy induces molecular vibration causing heating effects of tissue (thermodynamic interactions)

Question 15

Physical interactions induced by visible light lasers

Answer 15

Photochemical interactions by molecular bond dissociation

Can cause skin burns

Question 16

Use of CO2 laser

Answer 16

Surgical use e.g. gynae

Question 17

Argon-ion gas laser use

Answer 17

Ophthalmology

Question 18

Nd:YAG laser use

Answer 18

Dermatology

Question 19

Q switching

Answer 19

Pulsed emissions to allow dissipation of heat between short Laser bursts
Aims to reduce damage to neighbouring tissues

Used in Ophthalmology

Question 20

What determines penetration of laser beam

Answer 20

Wavelength

Longer wavelength absorbed more by tissue so has lower penetration (UV and infrared spectrum)

Question 21

CO2 Laser wavelength, penetration and main use in surgery

Answer 21

10,600 nm (far IR)

1 mm penetration

Used as bloodless cutter and vaporiser

Question 22

Argon Laser wavelength, penetration and main use in surgery

Answer 22

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

Question 23

Nd:YAG Laser wavelength and penetration

Answer 23

1064 nm (IR)

3 - 5 mm penetration

Absorbed by Hb, melanin and water

Question 24

Risks associated with LASER use

Answer 24

Eye damage - beams are non-divergent so distance does not add safety and reflected beams can still cause damage

Flammability - gases, drapes, ETT / cuff

Question 25

Safety mechanisms when using LASER in theatre

Answer 25

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

Question 26

Classification of LASERs

Answer 26

4 groups according to energy output

Class 1
Class 2
Class 3
Class 4

Question 27

Class 1 LASERs

Answer 27

Cannot emit radiation at any known hazard levels for the eye

Very low power output

Question 28

Class 2 LASERs

Answer 28

Low power visible lasers

Radiant power less than or equal to 1 mW

Question 29

Class 3 LASERs

Answer 29

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

Question 30

Class 4 LASERs

Answer 30

High power lasers >500 mW

Continuous beam

Very hazardous to view and hazard to skin too

Question 31

Most common class of LASER used clinically

Answer 31

Class 4