Part 1- Lasers
Among other treatments and modalities, Dermal Clinicians study lasers and IPL technology quite extensively. So, what are lasers?
The word LASER is an acronym meaning Light Amplification by Stimulated Emission of
Radiation. Particles of laser light (photons) are coherent or “in phase”, collimated low-
divergence beams consisting of one specific wavelength (a single colour) of light. Lasers have an extensive range of applications in the field of health and medicine; including treatment of skin disorders such as acne, vitiligo and melasma to name a few, treatment of nail disorders such as onychomycosis, tattoo removal, hair reduction, treatment for alopecia, skin resurfacing and tightening, treatment of vascular lesions, scar revision as well as the promising fields of laser assisted transdermal drug delivery.
How do they work?
Laser devices are made up of three components; an active/gain medium which determines the lasers wavelength and is in the form of either a solid (e.g.; crystals) liquid (e.g. organic dyes or solvents) or gas (e.g. argon or carbon dioxide), an energy input or pumping source which provides the necessary energy such as electricity, and optical resonators (mirrors). Theactive/gain medium is contained within the cavity of the laser device between two parallel
mirrors, one fully reflective at one end, and one partially reflective (known as the output coupler) at the other, allowing the energised photons to escape the laser as a beam. The laser device is often named after the type of lasing medium used. For example, the 755 nanometre Alexandrite laser used for hair removal among other functions, takes its name from the alexandrite crystal as its solid-state gain medium.
The physics of lasers starts with the atom containing a central nucleus with protons and
neutrons, and circling electrons within distinct orbital shells. Danish physicist Dr Niels Bohr’s
theory of spontaneous emission then described that once electrons move from their ground
state to the higher energy orbitals, they spontaneously return to their ground state, releasing the difference in energy between the two states as a photon, or quantum of light.
The collision of this photon with another atom in the excited state will stimulate the first atom to return to its ground state, releasing a second photon identical to the first in direction, phase, polarisation and energy. This process, called stimulated emission, describes the basic principle of laser energy creation. The parallel mirrors allow the rapid amplification of the stimulated emission process, ensuring enough photons are emitted to produce a continuous beam of laser light.
Diode lasers are also used in dermal settings and differ from other lasers in that they do not
require a laser cavity to produce photons, but instead produce photons within the machine’s
handpiece itself, making them smaller and easier to handle.
Lasers can operate in continuous mode, pulsed mode or Q-switched modes, depending on its intended use. For example, Q-switched lasers deliver very high energy nanosecond pulses intended to shatter tattoo pigment within the dermis for removal via the lymphatic system, without injuring surrounding tissue.
Laser radiation can be either ionising or non-ionising, the first is high energy characterised by short wavelengths and high frequencies and has the capacity to alter or damage DNA, such as; X-rays. Non-ionising radiation, the form used in dermal therapy laser treatments, has less energy, longer wavelengths, and lower frequencies than ionising radiation, and does not ionise matter.
Laser parameters include wavelength, energy and energy density, pulse durations, repetition
rate, duty cycle, power and power density and spot diameter. The most important parameter to consider when deciding on a laser for treatment is the laser radiation depth of penetration into tissue. The extent of tissue damage during laser interaction is determined by the lasers power density and wavelength, and the exposure time to the tissue.
When laser energy contacts matter it will either be reflected, refracted, scattered, absorbed or transmitted. Absorption is the desired process for laser skin treatments, the energy is then
responsible for biological responses within tissue. Energy is absorbed into primary target
chromophores; haemoglobin, melanin or water. The mechanisms by which lasers exert damage to target tissue are either photothermal, photoacoustic, photodissociation, photomechanical or photobiomodulation.
Light-Tissue Effects Explained
Photothermal reactions see the energy converted to heat within tissue, denaturing target cells such as keratinocytes or melanocytes when treating pigmentation, as one example. The principles of selective photothermolysis and extended theory of photothermolysis are used when the intention is to selectively damage only target tissues using heat, while preserving the surrounding tissue, for example when performing laser hair reduction treatments.
Photodissociation involves breaking intramolecular bonds resulting in cell death, a desired
response during skin resurfacing procedures. Photoacoustic or photomechanical reactions
result from high energy short pulses which generate shock waves within tissue causing
damage, and is then technique used during tattoo removal procedures.
Photochemical reactions involve the uptake of a photosensitising chemical by target tissue
resulting in cell death, and is the light-tissue interaction means used within photodynamic
therapy for the removal of lesions resulting from sun damage.
Photobiomodulation reactions either stimulate or inhibit cellular processes without tissue heating or destruction during low level laser therapy (LLLT) using light emitting diodes (LED’s). Biostimulatory effects include increased cellular energy and enhanced wound healing, while bio-inhibitory effects may be a reduction in pain and inflammation.
What are the general indications for laser use?
The uses for lasers in the field of dermatology are vast and constantly evolving. In terms of laser hair reduction, the ideal candidate has light skin and dark hair, allowing the technician to target melanin in the follicular stem cells in the bulge and bulb as the chromophore.
Vascular lasers such as the pulsed dye laser has a wavelength of 585-595nm which coincides with the absorption peak of oxyhaemoglobin, and is used to treat superficial blood vessels improving many congenital or acquired vascular conditions such as telangiectasias. Longer wavelengths from the Nd: YAG device can target deeper vasculature and improve venous lakes and port wine stains, for example.
Dermal Clinicians also use a multitude of laser wavelengths to treat pigmentary conditions, perform skin resurfacing to improve photoaging signs such as solar lentigines and rhytids, and improve the pliability and appearance of scars such as hypertrophic or keloid scars.
Lasers are also used to assist with treatment of atrophic acne scarring, the treatment of alopecia, rhinophyma which can occur as part of phymatous rosacea, and striae among many other conditions.
Laser safety and regulations
The application of lasers brings potential hazards which must be carefully managed to avoid
risks and injury. Laser hazards can be broadly classified as eye hazards, skin hazards,