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4
Description of the Unit
4.1
General Information on Laser Theory
LASER is an acronym meaning "Light Amplification by Stimulated Emission of Radiation". The
laser (light source) consists of an active medium and an excitation source. This excitation
source "pumps" the electrons of the active medium from their normal state into a stimulated
energy state (high energy level). The medium then starts to return to its normal state
(transition to lower energy levels). In this process, photons are emitted. The light is then
reflected multiply in an optical resonator (laser cavity) consisting of a highly reflecting mirror
and a partially transparent one. At the same time, it is amplified by induced emission while
traveling back and forth between the mirrors. Through the semitransparent mirror, part of the
laser light is coupled out and subsequently used for medical purposes.
Main characteristics of laser light:
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Highly parallel beams – very little beam divergence / spread.
Monochromaticity – light of a very narrow wavelength range, equivalent to a single color in
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the spectrum of electromagnetic radiation.
Coherence – all photons emitted are in phase (in terms of both space and time).
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The active medium (lasing material) can either be a gas, a liquid dye or a solid. Most gas
lasers consist of atoms or small molecules or a mixture of both. In the case of the solid-state
laser, the active medium consists of atoms or ions doped (bound) in a solid-state host crystal.
In the case of the dye laser, the active medium consists of molecules of a relatively high
molecular weight, dissolved in a liquid.
For the pumping energy that is needed, either direct current, high-frequency energy or – as in
the case of the solid-state laser – light is used. Under specific pumping energy conditions, the
so-called "population inversion" phenomenon can be observed with all of the above media.
This means that it is possible to induce laser light emission at a specific wavelength that is
characteristic for the active medium used. The high light intensity gain is achieved through
optical feedback by the mirrors of the laser resonator and through amplification by induced
emission each time the beam passes through the resonator.
20
Operating Instructions
Surgical Laser Unit Limax
®
120
V. 2.0
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