1. What is a Laser

Lasers take their name from the acronym Light Amplification by Stimulated Emission of Radiation, and consist of artificial light obtained by amplifying light (electromagnetic waves) using a resonator. Laser beams have such physical characteristics as excellent directivity and convergence, the ability to constantly maintain wavelengths, etc., and are used in leading edge processing applications with high added value.
In 1917 Albert Einstein announced his “Theory of Stimulated Emission” regarding lasers, indicating their possibilities. Thereafter, Theodore Maiman of the US succeeded in producing the world’s first laser oscillation using a ruby crystal in 1960. Subsequently, various laser oscillation phenomena were discovered by researchers around the world. The He-Ne laser and glass laser were discovered in 1961, semiconductor laser in 1962, Ar laser in 1963, CO2 laser in 1964, dye laser and picosecond laser in 1966, excimer laser in 1970, femtosecond laser in 1981, etc.

Next, what of the principles of lasers?
Normally, atoms and molecules move with a given specific energy. If they receive energy from an external source, these atoms and molecules move with a higher energy. This is called an excited state. After a while the atoms and molecules release this extra energy and return to their original energy state. At that time, the released extra energy is emitted externally as light. This is called “spontaneous emission.” When this light collides with other atoms and molecules that have high energy, light with the same properties is emitted. This is called “stimulated emission.” Normally, since the number of atoms and molecules with high energy is low, the emitted light is extremely weak, but if the number of atoms and molecules with high energy is increased by some method or other, stimulated emission occurs in an avalanche effect and strong light is emitted. This is light amplification. In addition, if mirrors are placed facing each other under certain conditions (this is called a resonator) and the emitted light is repeatedly reflected, the light is amplified in a specific direction and strengthened even further. This is the principle of lasers.

Characteristics of lasers
Separating the characteristics of laser beams into four major categories, there are (1) superior monochromatism, (2) superior directivity, (3) superior coherence, and (4) high output, and utilizing these characteristics, lasers are applied in various fields such as optical communications, laser processing, etc. In particular, laser processing is applied in many fields, utilizing the high output characteristic of (4). Here, we will introduce processing by means of an excimer laser.