Week 9 Flashcards
LASER acronym
Light Amplification by Stimulated Emission of Radiation
Quantum Physics
In 1917, Einstein proposed the possibility of stimulated emission, the physical process that makes the maser and the laser
Review components of the first ruby laser
Pg. 6
Low intensity laser therapy (LILT)
synonyms -therapeutic laser -low level laser therapy -low power laser therapy low level laser low power laser low energy laser soft laser low reactive level laser low intensity-level laser photobiostimulation laser photobiomodulation laser mid laser medical laser biostimulating laser bioregulating laser
Class of lasers
Class I : low power lasers Class II: power out put up to 1mW (400-700nm wavelength) Class IIIa: power out put up to 5mW Class IIIb: power output up to 5-500mW Class IV: Power output up to 500-700mW
Lasing medium
a substance of being ‘pumped’ with energy
gaseous mixture
-helium neon (He-Ne) red light 632nm
Gallium - arsenide (Ga-As) red light 632nm
*Gallium - aluminium-arsebude (GAAIAs) semiconductors visible red to near infra red 630-950nm
*cheaper, higher power, less dangerous to eyes
Resonating cavity
chamber to contain lasing medium
contains a pair of parallel reflecting surfaces / mirrors
Photons are reflected back and forth to produce an intense photon resonance
one reflecting surface (output coupler) is not a perfect ‘mirror’ and allows output of the light
Power source
a power source is required to ‘pump’ the lasing medium to produce stimulated emission
Usually mains supplied power but can be battery operated e.g. rechargeable NiMH x20AA
Characteristics of laser radiation
monochromaticity
collimation
coherence
Monochromaticity characteristics
single coloured
clustered around a single wavelength
wavelength is a critical factor for determining biological effect
Collimation characteristics
rays of light / photons are all parallel
almost no divergence over distance
optical power is ‘bundled ‘ on to a small area
but increases danger to the eye
Coherence characteristics
light emitted is in phase
troughs and peaks perfectly matched
-in time (temperal coherence)
-in space (spatial coherence(
And crawling on the planet’s face some insects called the human race lost in time, and lost in space and meaning
Laser tissue interaction LILT
Scattering of incident light
- change in direction of light as it passes through tissue with varying refractive indices relative to water content = loss of coherence
absorption of incident lightr
- chromophores are biomolecules that absorb photons and include melanin and haemoglobin
- therefore penetration is limited to several millimetres but is wavelength dependant
Laser tissue interaction LILT
of these two modes, absorption is the most important in terms of the photobiological basis of laser therapy
photobiological effects of laser
Multiple possible effects
complex interactions
irradiation parameters based
poorly understood