Electromagnetic Spectrum and Wavelengths
The word laser will be limited to electromagnetic radiation-emitting devices using light amplification by stimulated emission of radiation at wavelengths from 180 nanometers to 1 millimeter. The electromagnetic spectrum includes energy ranging from gamma rays to electricity. Figure 1 illustrates the total electromagnetic spectrum and wavelengths of the various regions.
Measuring Wavelengths: Nanometers (nm)
The biological effect of laser therapy is related to the wavelength of light emitted by the laser.
- Different wavelengths target different tissues e.g. blood, melanin, water, etc.
- These targets are known as Chromophores
- Ultraviolet radiation consists of wavelengths between 180 and 400 nanometers
- The visible light region is radiation with wavelengths between 400 and 700 nm
- The infrared light region (not visible) of the spectrum consists of radiation with wavelengths between 700 nm and 1 mm.
Light – Tissue Interactions
3 Types of Light – Tissue Interactions:
1. Photo – Thermal Lasers
Photothermal converts light energy into heat energy. This causes the tissue to heat up and vaporize. These lasers are “long pulsed”.
- Most surgical lasers
- Hair removal lasers
2. Photo –Mechanical (or Photo-Acoustic) Lasers
Photoablative causes photodissociation or breaking of the molecular bonds in tissue. These lasers are “short pulsed”.
- Q-switched lasers
- Tattoo removal lasers
3. Photo-Chemical Lasers
Photochemical causes target cells to start light-induced chemical reactions.
- Therapy lasers – treating pain in a joint or the deep tissues
- Photo-dynamic lasers (PDT) – cancer treatment, ophthalmic treatments
Wavelengths and Absorption
Laser light’s monchromaticity is responsible for its selective effect on biologic tissue. Whenever light hits tissue, it can be transmitted, scattered, reflected, or absorbed, depending on the type of tissue and the wavelength (color) of the light. However, light absorption must take place for there to be any biologic effect, and a given wavelength of light may be strongly absorbed by one type of tissue, and be transmitted or scattered by another. Infrared light is absorbed primarily by water, while visible and ultraviolet light are absorbed mainly by hemoglobin and melanin, respectively. As the wavelength decreases toward the blue-violet, and ultraviolet, scatter, which limits the depth that light may penetrate into tissue, becomes more significant. When light is absorbed, it delivers energy to tissue, and the tissue’s reaction depends on the intensity and exposure time of the light. Each type of tissue has its specific absorption characteristics depending on its specific components (i.e., skin is composed of cells, hair follicles, pigment, blood vessels, sweat glands, etc.). The main absorbing components, or chromophores, of tissue are:
- Hemoglobin in blood
- Melanin in skin, hair, moles, etc.
- Water (present in all biologic tissue)
- Protein or “Scatter” (covalent bonds present in tissue)
The Effectiveness of the 980nm Wavelength
Among diode laser wavelengths, 980nm lies at a peak in the light-water absorption curve, as neither water not hemoglobin is a strong absorber. This explains the deep penetration at this wavelength.
Common Lasers and their Wavelengths
The color or wavelength of light being emitted depends on the type of lasing material being used. For example, if a Neodymium:Yttrium Aluminum Garnet (Nd:YAG) crystal is used as the lasing material, light with a wavelength of 1064 nm will be emitted.
Table 1 illustrates various types of material currently used for lasing and the wavelengths that are emitted by that type of laser.
*Note that certain materials and gases are capable of emitting more than one wavelength. The wavelength of the light emitted in this case is dependent on the optical configuration of the laser.
Commentary on Wavelengths
By Jan Tunér, DDS
Lars Hode, DrSci (Swedish Laser Medical Society)
One laser manufacturer in the USA claims that their lasers produce “soliton waves” by “piggybacking one wavelength upon another”, and that these “penetrate deeper into the body than is possible with any other type of laser”. This sounds impressive and unique, but it is a sales trick, no more, no less. No therapeutic laser on the market produces solitons. And, even if it were possible and financially viable to do so, what evidence is there to support this manufacturer’s claims of therapeutic benefit?
The husband-and-wife “inventors” of the Scalar Wave Laser claim to have developed the “most advanced low level laser technology with state of the art quantum scalar waves” that supposedly employs a “unique approach to accessing the quantum neutral unified field state” to “dissolve cellular memory, normalize body systems, optimize anti-aging capabilities, and activate the glands and higher dimensional subtle body that yogis and mystics have tapped into throughout the ages”. This is, of course, a complete fabrication, a crackpot theory. No laser equipment designed for laser phototherapy is producing scalar waves and again, even if such waves existed, there is no evidence whatsoever that they should have a positive or negative effect of cell functions.
False Claims of Penetration
For many indications, some degree of light penetration through tissue is an advantage. The penetration of laser light into different types of tissue is surprisingly poorly investigated, but enough is certainly known to refute the claims of some manufacturers. There are two extremes oft found in the marketing claims, one that photons can penetrate clothes and even the entire body at very low powers, the other that very high power output is needed to reach very deep-lying targets. Both claims are characterized by gross exaggeration, demonstrating either complete ignorance or deliberate misapplication of the science of optics.
Treating through Clothes?
One particular manufacturer claims that their device, emitting a very low intensity thin line of red laser light, can be used to treat patients effectively through their clothing. Yet it is obvious to anyone who wears a shirt in the sun that clothes are a very effective blocker of light. And the skin barrier in itself reduces the amount of light going below the dermis.
A simple experiment on the penetration of 650 nm 20 mW red laser light through different types of textiles can be watched on the following YouTube presentation: http://www.youtube.com/watch?v=MkGJvvWD1vw.
Representatives of this company also claim that these photons go right through our bodies. Whilst it is possible for very high-energy particles such as neutrinos and for x-rays, being very different waves, to penetrate through our bodies, the low energy photons produced by therapeutic lasers are physically incapable of penetrating through that much tissue. Recent research is hinting that low power and long exposure is better than high power and short time for tissue regeneration, and, seemingly underlining this statement, this same company has presented research papers showing success using their lasers in the clinical setting (without clothes). Serious users of this approach report treatment times in excess of 15-20 minutes, which may produce a systemic effect by irradiating blood through superficial blood vessels. Well enough, but this does not involve photons penetrating the body, and certainly will not work through clothes. Mixing science with pseudoscience is pseudoscience.