Technical outlines

The last few points of this overview are meant to give you an idea of the technicity of such a treatment and of the importance for it to be carried out by a physician (often called a laserist).

The laser beam is transmitted by an optical fibre extended by a handpiece that allows the operator to see the skin when he shoots. The skin target area of the laser shot is called “spot”. It is a very intense light mark with a diameter of 7 to 18 mm (or sides measuring 9 to 12 mm). The surface of the skin must be entirely covered as homogeneously as possible by a succession of spots before the treatment.

The main parameters to be observed by the practitioner in order to reach optimum results are:

-The spot diameter: a large spot diameter (12 mm or more) provides a good skin penetration and is more efficient on deep hair. You will also be treated faster. Manufacturers are very good at creating devices able to deliver enough energy to obtain large spots. Only very performing devices can shoot 2 shots per second with a 15 mm spot or 3 shots per second with a 12.5 mm spot!

-The fluence (expressed in Joules/cm2): the cornerstone of the treatment. It defines the energy of the shot per unit of area. The practitioner is confronted to two contradictory objectives while choosing the fluence: being efficient by using high fluences, but remaining prudent so as not to burn the skin. An experienced practitioner will be able to use the highest fluence in order to obtain the most efficient results and durable satisfaction. He will thus analyse your skin type (phototype) and will observe the different skin reactions (hair crepitation, retraction, root expulsion, erythematous papular reaction, etc.) in order to be as close as possible to the maximum tolerated dose. Tests progressively increasing the fluence session after session are undergone for this purpose.

- The pulse time (or shot time): it is the laser emission time, which greatly conditions the efficiency of the treatment. The laser pulse time can be compared to a car transmission: it transmits energy according to a reduction ratio adapted to the different hair and skin types. A car with several gears is much more efficient ; similarly it is preferable for a laser to have several pulse times.

- The skin cooling: if the pulse time can be compared to the transmission, the cooling system can be compared to the tires. The choice of the tires gets harder when cars get powerful and when the transmission is sophisticated. Thus, a sophisticated cooling system is necessary for a good laser to deliver its power and to benefit from all the advantages of an adjustable pulse time. A performing skin cooling system allows an increase in both the efficiency and safety of the treatment, and maintains the patient’s comfort.

SOME MORE INFORMATION: the fluence is derived from power, and is also expressed in Watts/second/cm2. A laser must be powerful enough to deliver the fluence necessary to destroy the deepest hair. The necessary fluence depends strongly on the wavelength. It is relatively low with Ruby lasers, as its light is absorbed a lot by melanin (<20 J/cm2). It must be higher with Alexandrite lasers, even higher with diodes, and very high with an Nd : YAG. In practice, a practitioner often needs more power, may it be to increase the efficiency of a shot, to extend its duration, to increase the spot diameter, or to increase the fluence.