Cosmetic Medicine | Dr. Enrique Etxeberria, Plastic Surgery in Bilbao

Laser

Cosmetic Medicine - Laser - Laser

Laser

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WHAT IS LASER

The term laser is used to define the devices that generate a specific type of electromagnetic radiation, laser light.  Also, by extension, electromagnetic radiation itself is also called this.
The term laser is in effect an acronym.  It means Light Amplification by Stimulated Emission of Radiation).
This is a physical phenomenon which can be summarised in the following way:  some particularly sensitive substances, such as CO2 or Holmium (in other words so-called “laser substances”) when stimulated by a source of energy (generally by electrical current) liberate in turn part of the energy acquired in the shape of photons (spontaneous emission). The liberated photons can repeat the process by interacting with other electrons of the same substance which, in turn, are stimulated and liberate more photons (stimulated emission). The intensity of the resulting energy can be amplified by the photons being repeatedly reflected in two parallel mirrors placed in the device.  The ultimate effect is the production of a beam of photons, of the same intensity and physical characteristics, and equivalent to a quantity of energy superior to that used to stimulate the initial emission.

HOW A LASER DEVICE WORKS

Laser equipment consists of a cavity, generally in the shape of a cylinder, which contains the laser substance, a source of energy (generally a flash light), a coolant, a switch to control the intensity of the beam emitted and a series of mirrors which reflect the beam of light and modulate it. One of the mirrors tends to be completely reflective for the length of the laser wave and the other is a partially transmitting mirror. Once the laser light is formed, part of it escapes from the cavity through the partially transmitting mirror in the shape of a beam, or laser ray. Fiberscopes are generally used to conduct the light and aim it at the target tissue. Lasers invisible to the human eye (the majority of surgical lasers) tend to also incorporate a visible light beam by way of guide (generally a diode laser or Helium-Neon laser).

CHARACTERISTICS OF LASER LIGHT

Laser radiation occupies a large part of the electromagnetic spectrum although, generally, close to the visible part.  Its specific position depends on the wavelength, which is the principal parameter delimiting the rate of absorption of light by the tissues (absorption coefficient). Lights with a wavelength of between 400 and 750 nanometres (nm) are located within the visible range of the spectrum; those that are under 400 nm through to 10nm constitute the ultraviolet spectrum, while waves of 750 nm to 106 nm make up the infrared spectrum.  Lasers commonly used in surgery occupy anything from the ultraviolet range (excimer, with 193 nm) to the infrared range (CO2, of 10.640 nm).

Unlike other types of light, laser light from one same active substance transmits one sole frequency or wavelength (it is monochromatic), and in one same direction, in a parallel and narrow beam.  These two characteristics are called coherence (spacial and temporal) and they are what permits laser light to be specifically absorbed by certain tissue components and to be concentrated and focussed by conventional lenses and fibres.  Normal light, on the other hand, is made up of multiple random wavelengths.

The frequency of the wave emissions (their temporal relation) significantly determines the effect of the laser on the tissue.  The frequency of emission is considered to be continuous when the laser light oscillates in pulses of more than 0,25 s, resulting in the liberation of a constant quantity of energy, but which is less than that emitted by so-called pulse lasers. These, on the other hand, emit in intervals in the order of milliseconds (normally between 10 and 100ms) and therefore permit greater coverage of the amplitude of the pulse (or duration) with an increase corresponding to its strength and cutting precision. The term super pulse refers to lasers of great strength with an even shorter pulse length, while those of giant pulse have extremely short pulses and, therefore, very high intensities.

SURGICAL LASERS

Ever since laser energy began to be used in surgery, a great variety of wavelengths have been developed in response, fundamentally, to the different affinities of the tissue, as well as the anatomical characteristics of the target organs and the physiological media in which the laser must operate (gaseous, in open bone surgery, or liquid in urology).  On the other hand, to obtain it in sinuous, narrow or remote tissues, the laser light must be able to be transmitted by small and flexible fiberscopes.

All these requirements have determined the development of a series of electromagnetic waves, used by the most widely used surgical lasers, amongst which of note are the following:
Carbon dioxide-CO2
The CO2 laser is known as the battle horse of laser surgery due to its wide range of applications.  It emits an invisible wavelength of 10.600 nm (10,6 m) and is quickly absorbed in water, permitting precision cutting (vaporisation of cellular water) without causing significant lesions in the adjacent tissue. Precisely because of this, it cannot be used when the environment it must cross is liquid as the energy is absorbed prior to reaching the target tissue.  It must be distributed through an articulated very unpractical arm which limits its use.
Ionized gases
Neutral gas lasers, such as argon, neon, krypton and xenon are used in medicine for various purposes.  The argon laser, which emits in two visible wavelengths, at 488 and 514 nm, is much used in ophthalmology.
Dye lasers
Dye lasers normally emit normally pulse mode and at different wavelengths depending on the dye used.  In liquid media they produce an intense acoustic effect (used in lithotripsy).  Its use is limited because it is absorbed in a very selective manner by different components but not by water.
Neodymium: YAG
This is one of the most common lasers in surgery.  It is a solid laser which emits at an invisible wavelength of 1.064 nm (a modified form is the Q-switched Nd:YAG or KTP/532 which emits at 532 nm). This laser can be transmitted through fibre optics but is not absorbed well in water, and therefore its cutting capacity is imprecise and generates a large quantity of lateral damage.  It is a good haemostatic.