Glossary of Terms


Common terms used in reference to laser technology and specific conditions and treatments.

Ablation
Learn more
Tissue removed by laser vapourisation (phase transition from liquid to gas by boiling).
Close
Absorption
Learn more
Photoabsorption of energy by tissue. Linear for visible absorption spectrums. Energy is transferred to tissue.
Close
Absorption coefficient
Learn more
Attenuation coefficient. Characterises how easily a material can be penetrated by light.
Close
Absorption peak
Learn more
Maximal absorption of chromosphere on absorption curve.
Close
Active medium
Learn more
Medium by which the laser is known (eg CO2 laser).
Close
ALA
Learn more
Aminolevulinic acid – photoactive porphyrin (5-ALA or methyl-ALA).
Close
Angioma
Learn more
Capillary haemangioma – mass of tiny blood vessels – flat or raised.
Close
Attenuation
Learn more
Light in tissue dissipates progressively. Attenuation coefficient (absorption coefficient).
Close
Beam delivery
Learn more
Laser beam by way of articulated arm by mirrors or via fibreoptic cable.
Close
Beers’ law
Learn more
The Beer-Lambert law states that there is a logarithmic dependence between transmissivity of light through a substance and the product of the absorption coefficient and the path length.
Close
Biologic effects
Learn more
Tissue effects of light which can be photothermal, photomechanical or photochemical.
Close
Biostimulation
Learn more
Low intensity lasers in the red/IR range may produce beneficial microcirculatory effects to stimulate cellular processes.
Close
Caviation
Learn more
Formation of a cavity eg by ‘Q’ switched or other very short pulsed wide lasers.
Close
Chromophore
Learn more
A part of the molecule responsible for its colour. The colour is seen when that molecule absorbs certain wavelengths and transmitted or reflects others.
Close
Class
Learn more
Referring to lasers (medical) – Class I – IV.
Close
CO2 laser
Learn more
Carbon dioxide lasing medium giving a far infrared (10600nm) output.
Close
Coagulative necrosis
Learn more
Cell death with denatured proteins (structural and lysosomal) caused in this context by light induced tissue heating >62°C.
Close
Coherent
Learn more
Waves in phase (laser).
Close
Collimated
Learn more
Waves parallel – no convergence or divergence.
Close
Continuous wave (CW)
Learn more
Laser beam present continuously while in operation. Sometimes pulsed CW.
Close
Corneal shields
Learn more
Eye protection placed directly onto cornea under topical anaesthesia.
Close
DCD
Learn more
Dynamic cooling device (cryogen spray pre-treatment of skin).
Close
Defocussed
Learn more
In clinical laser practice a beam can be ‘defocussed’ by a ‘pullback’ technique.
Close
Delivery System
Learn more
Transmission of EMR to treatment site - optical fibres for shorter wavelengths up to 1500nm, articulated aims generally beyond that.
Close
Density
Learn more
Referring to the density (percentage coverage) of microthermal zones in fractional photothermolysis.
Close
Dermis
Learn more
Deeper layer of skin giving structural strength and containing blood vessels and adnexae.
Close
Divergence
Learn more
Laser beams have low divergence - ideally no divergence. Beams are parallel.
Close
Ectatic
Learn more
Dilatation of hollow structure (vessel) – from the Greek.
Close
Electromagnetic Spectrum
Learn more
Range of wavelengths from ultraviolet to radio waves.
Close
EMR
Learn more
Electromagnetic radiation (includes UV, visible light and IR wavelengths) as well as X-rays and radio waves.
Close
Energy
Learn more
Refers to radiant energy of electromagnetic waves. The unit of energy is the joule (J). The unit of energy per unit time is a watt (W) which is power.
Close
Epidermis
Learn more
The outer layer of skin. The thickness of the epidermis varies depending on anatomical site.
Close
Er: glass
Learn more
Erbium doped glass (silicate/phosphate) laser emitting at 1550nm.
Close
Er:YAG
Learn more
Erbium doped YAG (Yttrium aluminium garnet) laser emitting at 2940nm.
Close
Erythema
Learn more
Redness (of the skin).
Close
Excimer laser
Learn more
‘Excited dimmer’ laser utilising noble gas halides to deliver a number of different UV wavelengths. XeCe @ 308nm.
Close
Excitation
Learn more
Gas lasers are excited electrically and solid-state and liquid lasers are optically pumped.
Close
Flash lamp
Learn more
Flash tube electric are lamp producing intense, incoherent full spectrum white light for very short durations through ionisation of xenon gas.
Close
Fluence
Learn more
Radiant exposure (energy per unit area – normally joules cm2).
Close
Focal length
Learn more
Distance between lens and focal point.
Close
Focussed
Learn more
Collimated laser light can be focussed through optical lenses.
Close
Frequency
Learn more
Temporal frequency is the number of occurrences per unit time and is the reciprocal of the period (as in wavelength and frequency).
Close
Gating
Learn more
Mechanical structure to produce a pulsed beam.
Close
Gaussian
Learn more
Bell curve shape characteristic of most laser beam output profile. Not suitable for ‘Q’ switched energy delivery.
Close
Hazard Classification
Learn more
Direct and indirect viewing hazardous – applies to all class 4 lasers.
Close
Holmium
Learn more
A rare earth element used to ‘dope’ lasing media – often together with other rare earths such as Erbium and Thulium.
Close
Hyperpigmentation
Learn more
Excessive colour often after inflammation (PIH) post inflammatory hyperpigmentation. May be a racial tendency.
Close
Hypopigmentation
Learn more
Loss of skin pigmentation. May be post injury, postinflammatory,immunological, genetic or idiopathic.
Close
Intensity
Learn more
Power density or irradiance.
Close
Irradiance
Learn more
Fluence per unit time. Power delivered per unit area (power density).
Close
Keloid
Learn more
Nodular mass of scar tissue which continues to develop over time and spreads beyond the initial site.
Close
Kirchhoff’s laws
Learn more
A hot object produces a continuous spectrum - a hot rarefied gas produces an emission line spectrum. A cool gas in front of a continuous light source produces an absorption line spectrum.
Close
KTP
Learn more
Potassium titanyl phosphatase (frequency doubling crystal) used to halve Nd:YAG 1064nm wavelength to 532nm.
Close
KTP laser
Learn more
532nm (wavelength halved) Nd:YAG laser at 1064nm.
Close
Laser
Learn more
Light amplification by stimulated emission of radiation (an acronym).
Close
Laser medium
Learn more
Solid state (eg Nd:YAG), gas (eg CO2) or liquid (eg dye). Produces light of a particular wavelength.
Close
Lentigines
Learn more
Pigmented epidermal macules – sun exposed surfaces – benign.
Close
Melanin
Learn more
Pigment from active melanocytes (skin type dependent) eumelanin and pheomelanin.
Close
Melanocytic naevi
Learn more
>0.5mm diameter (usually acquired), otherwise lentigines.
Close
Melanosomes
Learn more
Melanin containing organelles (giant in café au lait macule - CALM).
Close
Microsecond
Learn more
10-6 seconds (0.000001 second).
Close
Microthermal zone
Learn more
MTZ is the submillimetre pathway through tissue in fractional photothemolysis.
Close
Millisecond
Learn more
10-4 seconds (0.0001 second).
Close
Monochromatic
Learn more
The coherent light emitted by lasers (distinct from polychromatic) is of an individual (pure) wavelength.
Close
Nanosecond
Learn more
10-9 second (0.0000000001 seconds).
Close
Nd:YAG
Learn more
Neodymium: yttrium aluminium garnet. Solid state lasing medium which emits radiation at 1064nm.
Close
Optical coupling
Learn more
With a light skin can be enhanced with water, alcohol, gel or oil as well as used with dermoscopy.
Close
Optical density
Learn more
(OD). A measure of the extent to which a substance transmits light.
Close
Optical interface
Learn more
At which light passes from one medium to another.
Close
Photoablation
Learn more
Light induced ablation/vapourisation of tissue which may occur with no thermal effect (Excimer laser).
Close
Photoacoustic
Learn more
Light that generates an acoustic shock wave in tissue (akin to thunder following lightening).
Close
Photochemical
Learn more
Light induced chemical change in tissue following absorption of visible, UV or IR radiation.
Close
Photochemotherapy
Learn more
PUVA. Oxsorolen is ingested and acts as a photosensitiser with UVA.
Close
Photodynamic therapy
Learn more
(PDT). Aminolevaline acid is activated by various visible light sources.
Close
Photomechanical
Learn more
Light induced mechanical (fracture) change in tissue utilising extremely high power densities delivered in extremely short pulses.
Close
Photon
Learn more
An elementary particle, the quantum of light and other forms of electromagnetic radiation. Characterises light – tissue reactions at a molecular level.
Close
Photothermal
Learn more
Light induced heat change (various types) in tissue.
Close
Plank’s Law
Learn more
Energy is proportional to frequency and inversely proportional to wavelength. High temperature objects emit high energy photons (shorter wavelengths) E=hc/λ.
Close
Poikiolderma of Civatte
Learn more
Pigmentation and telangiectasia (sides of neck) sun. Induced/genetic.
Close
Port wine stain
Learn more
Vascular malformation – complex heterogeneous congenital vascular lesion.
Close
Power
Learn more
Rate of energy delivery watts (W) = J/s. Overall ‘strength’ of laser beam.
Close
Power Density
Learn more
This is critical to effect on tissue with increased power through lens focusing.

Power / Beam Area = W/cm2
Close
Pulse repetition
Learn more
Rate of pulse generation (per second – Hertz).
Close
Pulse width
Learn more
Pulse duration measured by photodiodes. Determines the rate of delivery of laser power.
Close
Pulsed dye laser
Learn more
(PDL). A rhodamine dye solution is used as a lasing medium. Various wavelengths can be emitted, depending on additives. The Vbeam Perfecta™ emits at 595nm.
Close
Pulsed mode
Learn more
In contrast to continuous mode. Modern medical lasers are pulsed. Energy is released over very short time spans.
Close
Quality switched
Learn more
‘QS’. Rapid gating of laser output enables high peak power over very short periods leading to photomechanical effects.
Close
Reflection
Learn more
Photons reflected from the skin’s surface.
Close
Refraction
Learn more
Photons knocked ‘sideways’ within the skin.
Close
Remittance
Learn more
Photons sent back out through the skin and ‘lost’.
Close
Repetition rate
Learn more
Hertz rate of laser pulsing.
Close
Resonator
Learn more
Laser cavity/tube. Where the laser energy is produced.
Close
Rhodamine
Learn more
Lasing medium for pulsed dye laser.
Close
Scatter
Learn more
Deflection from a straight path through tissue - changes in direction.
Close
Selective photothemolysis
Learn more
Chromophore absorbs strongly with sparing of adjacent structures.
Close
Spatial coherence
Learn more
Describes the correlation between signals at different points in space.
Close
Spectral Lines
Learn more
Each element produces its own unique set of spectral lines when it emits light. Spectral lines occur when an electron jumps from one energy level to another and is the result of interaction between a quantum system and a photon.
Close
Spectroscopy
Learn more
Analysing components of light received from objects. Can also determine velocity (redshift).
Close
Spot size
Learn more
1mm+ up to 12mm for most current cutaneous lasers.
Close
Stimulated emission
Learn more
Is the process by which an atomic electron interacts with an electromagnetic wave drops to a lower energy level thereby transferring its energy to that field.
Close
Telangiectasia
Learn more
Fixed, dilated vessels (x Greek).
Close
Thermal
Learn more
The thermal mechanism involves conversion of laser energy into heat.
Close
Thermal relaxation time
Learn more
’T’. Time taken for a chromophore to cool to 50% of its base state.
Close
Thermoelectric cooling
Learn more
(TEC) System for contact cooling, which utilises the heat flux between two different metals. Also known as a Peltier device.
Close
Top Hat
Learn more
Flat topped beam profile giving the optimal shape for power output in many laser applications. May be made up of micro-pulses or pulse trains as in the pulsed dye laser.
Close
Transmission
Learn more
Where no energy is lost during passage through tissue.
Close
Transmissivity
Learn more
Measure of the ability of a material to transmit EMR.
Close
Wavelength
Learn more
The special period of a sinusoidal wave.
Close
Wien’s Law
Learn more
The dominant wavelength of radiation emitted by a blackbody is inversely propositional to its temperature. λmax = 2.9 x 103/T.
Close
Xenon arc
Learn more
Bright white light produced by passing electricity through ionised xenon gas. Mimics sunlight and has multiple absorption spectra.
Close

This page is best viewed in an up-to-date web browser with stylesheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so. The latest version of Firefox, Safari, Google Chrome or Internet Explorer will work best if you're after a new browser.