Fig. 3.1
Electromagnetic spectrum of light from gamma rays to radio wave wavelengths, UV ultra-violet or ultraviolet, IR infra-red or infrared
3.3 Characteristic of Ordinary Light and Property of Laser Light
Light is an electromagnetic radiation which besides its wave characteristic has a photonic corpuscular characteristic that transports a defined amount of energy (quantum).
The ordinary visible light, both natural (solar) and artificial, has several characteristics that must be defined to understand the laser light properties.
The ordinary light is disorderly emitted, because of the absence of coherence in the time and space of the photons; consequently the light is scattered in all the directions and diffuses homogeneously. The ordinary light is multichromatic, being composed of all the wavelengths and colors within the visible spectrum and also called white or achromatic light.
The basic colors of the visible light are violet, blue, cyan, green, yellow, orange, and red (Table 3.1).
Table 3.1
Basic colors of the visible light
|
Violet 380–450 nm
|
|
Blue 450–475 nm
|
|
Cyan 476–495 nm
|
|
Green 495–570 nm
|
|
Yellow 570–590 nm
|
|
Orange 590–620 nm
|
|
Red 620–750 nm
|
When the sunlight diffuses through the water droplets remained in suspension after a meteorological phenomenon such as a storm or a natural phenomenon such as a waterfall, the light can scatter and refract itself within the water droplets, producing the phenomenon of rainbow, that described the colors of the visible spectrum of the light.
Primary colors (or absolute colors) are the basic colors from which are obtained, combining them, all the others: they are red, blue, and yellow. The additive or subtractive combination of primary colors is used to obtain secondary colors; this concept helps to understand the use of complementary colors in photodynamic therapy and photoactivated dental bleaching (read ahead). The blue (420–470 nm) is the complementary color of yellow. The cyan (480 nm) is the complementary color of red (630–760 nm), and the magenta (that is a secondary color produced by combination of blue and red) is the complementary color of green (490–570 nm).
The laser light is different from the ordinary light, being able to aim a high amount of energy in a limited space in the form of light radiation.
Several characteristics differentiate laser light from ordinary light:
-
Laser light is collimated, that is to say that the waves, thanks to the spatial coherence of emitted photons, have only one very focused direction.
-
Laser light is coherent, that is to say that each wave/photon has the same phase with the other emitted waves/photons that are kept in time and space.
-
It is monochromatic, that is to say that each photon has just one wavelength and just one color (if visible) (Table 3.2).Table 3.2Property of laser and ordinary lightCharacteristicsLaser lightOrdinary lightDirectionCollimatedOne very focused directionNoncollimated or multidirectionalTemporal phaseCoherentEach wave/photon has the same phase with the other emitted waves/photon that are kept in timeNoncoherent or disorganizedColorMonochromaticOne wavelength and just one color (if visible)Multichromatic from 400 to 700 nm
3.4 Basic Component of Lasers
Several components are necessary to constitute a dental laser unit:
1.
The optical cavity (or resonator) that includes the active medium
2.
The active medium which characterizes different wavelengths of specific lasers
3.
The pumping source (or energy source) to supply the energy necessary for the stimulation
4.
A controller that is a software that controls the modality and parameter of laser emission and a cooler, necessary for cooling the laser system
5.
The delivery system that transports the laser energy to a terminal handpiece and tips and finally to the tissue (Table 3.3)
Table. 3.3
Basic components of a laser
|
Optical cavity
|
|
Active medium
|
|
Pumping source
|
|
Controller
|
|
Cooler
|
|
Delivery system
|
|
Handpiece and tips
|
3.4.1 Optical Cavity
It is a hollow cavity that contains the active medium and two mirrors located at its extremities; one is completely reflective, while the other one is partially reflective and permeable.
The excitement of the active medium by an external source of energy produces the stimulated emission of photons that, reflecting on the mirrors of the cavity and passing through the active medium many times, add their energy via an amplification phenomenon before coming out from the partially permeable mirror.
3.4.2 Active Medium
It is the heart of the laser and can be a solid, a liquid, a gas, or a semiconductor in the case of diode laser. The active medium determines the specific wavelength of different lasers and its name identifies different lasers. Table 3.4 reports the active medium of lasers mostly used in dentistry.
Table 3.4
Active media, hosting media, and doping atoms of the most used lasers in dentistry
|
Laser
|
Abbreviation
|
Active medium
|
Hosting medium
|
Doping atom
|
Wavelength (nm)
|
|---|---|---|---|---|---|
|
Argon
|
Ar
|
Gas
|
–
|
–
|
488 and 514
|
|
Carbon dioxide
|
CO2
|
Gas
|
–
|
–
|
9,300, 9,600, and 10,600
|
|
Diode
|
–
|
Semiconductor
|
–
|
–
|
445, 635–810, 940–970, 1,064
|
|
Potassium titanyl phosphate
|
KTP
|
Solid
|
YAG crystal
|
Neodymium frequency doubled
|
532
|
|
Neodymium-doped yttrium-aluminum-garnet
|
Nd:YAG
|
Solid
|
YAG crystal
|
Neodymium
|
1,064
|
|
Neodymium-doped yttrium-aluminum-perovskite
|
Nd:YAP
|
Solid
|
YAP crystal
|
Neodymium
|
1,340
|
|
Erbium-doped yttrium-scandium-gallium-garnet
|
Er,Cr:YSGG
|
Solid
|
YSGG crystal
|
Erbium and chromium
|
2,780
|
|
Erbium-doped yttrium-aluminum-garnet
|
Er:YAG
|
Solid
|
YAG crystal
|
Erbium
|
2,940
|
The active medium supplies the electrons for the production of the laser photons.
3.4.3 Pumping Source (or Energy Source)
The pumping source excites the atoms of the active medium producing the inversion of the population of electrons. This source of energy is usually represented by an electric coil or a diode laser or a flash lamp. The characteristics of pumping source are important for the generation of the laser pulse, especially for short-duration pulses (high peak power).
Stay updated, free dental videos. Join our Telegram channel
VIDEdental - Online dental courses
