Laser Hair Removal - Terms

Laser
Laser stands for "light amplification by stimulated emission of radiation." Lasers rely on electrons for this emission of radiation. Electrons spin round a nucleus at specific energy levels or states that are characteristic of a particular atom or molecule. On a simplistic level they are like satellites orbiting the Earth. The electrons that orbit furthest away from the nucleus are at higher energy levels than those nearer to the nucleus.

These electrons can be pushed into higher energy levels by giving them energy, simply by flashing a light at them. This excites the electron and it moves to a higher energy state, however once the external energy source is removed the electron drops from an outer level to an inner level and the "excess" energy is given off as light. Each wavelength of light is a different colour and is related to the amount of energy released.

Depending on the particular material that is used for the laser, specific wavelengths of light will be absorbed and emitted. If the whole process takes place in a mirrored chamber the reflected light will cause the same reaction in other atoms. As the light is reflected around the mirrored walls it is amplified and if the chamber has an aperture (hole) the escaping laser beam is almost entirely a single wavelength ( monochromatic).

Wavelength
For the purposes of this website light behaves as a wave (in some circumstances it behaves as a particle but that is a different story). The wavelength is defined as the distance between two corresponding points of two consecutive waves (eg, crest to crest or trough to trough).

Pulse duration
The length of time the laser is in touch with the skin. This can be controlled by using a Q-switch (similar to a camera shutter). The usual pulse duration is 1 -3 ms.

Energy density
The amount of energy (usually measured in Joules) per surface area of skin exposed (usually measured in square cms)

Selective photothermolysis
Photothermolysis comes from the Greek for "destruction from heat caused by light". Photo meaning light, thermo meaning heat and lysis meaning destruction. The term photothermolysis was originally proposed by Anderson et. al. in 1983 ( Anderson RR, Parrish JA. Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation. Science 220:524-527, 1983).

Melanin
A dark pigment produced by cells called melanocytes in the skin. Melanin absorbs ultraviolet, UV radiation and is therefore a natural sunscreen. Exposure to UV radiation stimulates more melanin production, resulting in a tan. Dark-skinned people naturally produce much more melanin than fair-skinned types and so are less liable to experience sunburn or skin cancer.

Epidermal cooling
Epidermal cooling simply means to cool the skin during treatment that allows higher pulse widths and energy densities to be used.

Four types of cooling are generally used:

> Clear (usually chilled) gel
> Contact cooling through a window cooled by circulating water
> Cryogen spray before and after the laser pulse
> Air cooling