Laser Principles

What is a "Laser"

Laser is defined as a high-energy light source emitted by the natural vibrations of atoms (of a gas or solid material) that is able to cut, burn or dissolve.

What does "Laser" stand for?

Laser stands for Light Amplification by Stimulated Emission of Radiation.

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Laser characteristics

Differences between a laser and ordinary light

Unlike an ordinary light source such as a lamp, lasers provide the following features:

Highly directional:
Laser light beam travels straight with almost no divergence. On the other hand, light from an ordinary lamp diverges in every direction.
Highly monochromatic:
Lasers emit a light beam with a single pure color (wavelength and frequency). An ordinary lamp emits a light beam with many colors mixed.
Highly coherent:
Laser provides excellent coherency (uniform phase of light relative to time) resulting in high amplitudes (higher outputs). Ordinary light produces an inconsistent phase of light with respect to time.
  Directivity (Straight beam) Monochrome light Coherence
Ordinary
light
Laser
beam
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Laser Types

Laser Classifications

A laser can be generally classified into the following three types:

Laser Classifications

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CO2 Laser

A CO2 laser is used mainly for machining and marking applications.
CO2 lasers emit invisible infrared beams with a wavelength of 10.6 μm. N2 gas serves to increase the energy level of CO2, and He gas serves to stabilize the CO2 energy level.

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YAG laser(Nd：YAG)

A YAG laser is used for general-purpose marking applications such as marking on plastic and metal workpieces, as well as for machining applications.
YAG lasers emit invisible near-infrared beams with a wavelength of 1064 nm.

Description of YAG

YAG is a solid that provides a crystalline structure of Y (yttrium) A (aluminum) G (garnet). Through doping of a light-emitting element, in this case Nd (neodymium), the YAG crystal will enter the excitation state via absorption of light from a Laser Diode.

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YVO4 laser (Nd：YVO4)

A YVO4 laser is used for ultra-fine marking and machining applications.
YVO4 lasers emit invisible near-infrared beams with a wavelength of 1064 nm, like the YAG laser.

Description of YVO4

YVO4 is a solid that provides a crystalline structure of Y (yttrium) V (vanadium) O4 (oxide), or Y (yttrium) VO4 (vanadate). Through doping of a light-emitting element, in this case Nd (neodymium), the YAG crystal will enter the excitation state via absorption of light from a Laser Diode.

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Wavelength Comparison

Wavelength Comparison

There are two types of laser markers that are used in industrial laser marking devices: YAG or YVO4 laser markers and CO2 laser markers. The difference between them lies in the wavelength of their laser beams.

Wavelength of SHG (Green Lasers)→ 532 nm
Wavelength of YAG or YVO4 Lasers→ 1064 nm
Wavelength of CO2 Lasers→ 10.6 μm

YAG or YVO4 lasers in comparison to CO2 lasers, have a wavelength that is 1/10 as short, which means that they have low reflectivity on metal surfaces, have reduced energy loss, and are easy to use for processing metals. Additionally, because CO2 lasers in comparison to YAG or YVO4 lasers, have a wavelength that is ten times as long, they are easily absorbed by glass and are suited for marking transparent objects. However, the completion of a marking will differ not just by the differences in wavelength, but will also depend on differences in power. Please keep this in consideration.

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Laser Oscillation Fundamentals

This explains the fundamentals up until a laser is oscillated.

(1) Absorption

As external light is injected, the electrons within the atoms absorb the light and go from the lowest state of energy (ground state) to a state of high energy. As the energy increases, the electrons transfer from normal orbits to exterior orbits. This state of increasing energy is called "Excitation".

Absorption

(2) Natural Emission

Excited electrons, in response to the amount of energy absorbed, rise in energy levels. Electrons that have been heightened with energy try to stabilize as a certain relaxation period passes, emitting energy in an attempt to return to a lower energy state. At this time, the emitted energy is emitted with light of the same energy.
This phenomenon is called "natural emission".

Natural Emission

(3) Stimulated Emission

As seen in the illustration below, electrons exist in a high-energy state and when the energy held by these electrons is injected with light of the same energy, it will emit light of exactly the same energy, phase, and movement direction.
In other words, what was a single photon during injection, produces a phenomenon where it becomes two photons. This is called "Stimulated Emission". Light produced from stimulated emission possess uniform energy, phases, and movement direction. Thus, producing a multitude of light with stimulated emission will allow for the creation of strong light with those three elements set uniformly.
Laser light is created by amplifying injected light using the phenomenon of stimulated emission.
Due to this, it possesses the characteristics of being (1) monochromatic (All light energy is equal), (2) coherent (uniform phases), and
(3) high-directional (uniform movement direction).

Stimulated Emission

(4) Population Inversion State

In order to oscillate a laser beam using natural emission, it is necessary to increase the density of electrons in a high-energy state to a density that is overwhelmingly higher than electrons in a low energy state. This is called a "Population Inversion State".
In other words, by having the amount of naturally emitted light exceed the absorbed light, it became possible to effectively create a laser beam for the first time.

Population Inversion State

(5) Laser Oscillation

In a population inversion state, when a single electron naturally emits light, that light will cause a different electron to naturally emit light. This will produce a chain reaction that increases the amount of light and creates a strong beam. This is how laser oscillation works.

Laser Oscillation

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Laser Oscillation Tube Elements

Three elements of a laser oscillation tube

All laser oscillation tubes are comprised of the following three elements:

(1) Laser medium
(2) Excitation source
(3) Amplifier

Three elements of a laser oscillation tube

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