**2. Principle of laser**

The principle of Light amplification by stimulated emission of radiation (LASER) was first hypothesized by Albert Einstein in the year of 1917 but it took almost half a century to construct a working laser. Around 1960, a first experimental setup of working industrial laser is developed. In many cases, the laser is different from the normal light in a way that it carries photons of higher frequencies. However, in some cases, the infrared laser has photons with low frequency than normal light. The frequencies of all the photons contained in a laser light are all same hence laser is characterized by coherence. The photons carried by a light can stimulate the electrons in an atom therefore it emits same frequency photons [3]. Based on this principle, laser produces high energy coherent light. Since laser is the fundamental part of any laser-based system, it is essential to understand the principle of laser light production.

Stimulation and amplification is the process (called as lasing) by which laser system converts electrical energy into a light of high intensity energy. The medium by which the lasing process carried out is called lasing medium. In any model of an atom, positively charged nucleus is surrounded by negatively charged electrons rotating at some specified path called orbits. The diameter and geometry of the orbit vary based on many parameters including number of electrons, surrounded magnetic field, structure of electrons and the existence of neighbor atoms. Every electron presents in the orbital connected with a distinctive energy level. An atom is said to be at ground level when it is at absolute zero temperature in which all the electrons reside in their lowest potential energy. Energy from any exciting sources such as electronic pulsation at higher temperature, chemical reaction or photon can be absorbed by an electron at ground level. After absorbing the energy, it excites to a higher energy level as schematically shown in **Figure 1**. Thus the movement of electron from lower to higher energy level is accomplished. Upon reaching higher energy levels, electron attains an unstable energy band. Immediately within very short time (tens of nanosecond) it starts moving back to ground state by releasing

**89**

**Figure 3.**

**Figure 2.**

*Excitation between energy levels.*

*Excitation between energy levels.*

*Laser Machining*

*DOI: http://dx.doi.org/10.5772/intechopen.93779*

electrons in various energy levels are shown.

a photon and this process is termed as "spontaneous emission." The frequency of

Sometime, when the electrons put into a meta-stable band due to energy change, the electron stays in the higher energy level itself for a short time (micro to milliseconds). The state by which more number of electrons stays in meta-stable energy level compared to the atoms in the ground level of a material is called "population inversion." These electrons are stimulated by suitable energy or frequency photons to come back to ground state. Photons emission due to this stimulated return of electrons is termed as "stimulated emission." In this way, the emitted photons along with one original photon temporarily having some spatial phase would create coherent laser beam. From the schematic representation of stimulated absorption, spontaneous emission, and stimulated emission as shown in **Figure 2**, position of

emitted photon would be equal to the frequency of exciting photon.

**Figure 1.** *Excitation between energy levels.*

## *Laser Machining DOI: http://dx.doi.org/10.5772/intechopen.93779*

*Practical Applications of Laser Ablation*

applications and limitations of using LBM.

principle of laser light production.

**2. Principle of laser**

by independency to hardness property of work material. LBM is gaining attention among the researchers and industry people because of its advantages such as higher light intensity with low power requirement, good focusing property within short duration of pulse, uniform heat distribution, eco-friendly nature which results in accuracy in machining, narrow heat affected zone, increased productivity and reduced manufacturing cost [2]. The upcoming sections describes in detail about the principle of laser and its types, mechanism of laser machining, advantages,

The principle of Light amplification by stimulated emission of radiation (LASER) was first hypothesized by Albert Einstein in the year of 1917 but it took almost half a century to construct a working laser. Around 1960, a first experimental setup of working industrial laser is developed. In many cases, the laser is different from the normal light in a way that it carries photons of higher frequencies. However, in some cases, the infrared laser has photons with low frequency than normal light. The frequencies of all the photons contained in a laser light are all same hence laser is characterized by coherence. The photons carried by a light can stimulate the electrons in an atom therefore it emits same frequency photons [3]. Based on this principle, laser produces high energy coherent light. Since laser is the fundamental part of any laser-based system, it is essential to understand the

Stimulation and amplification is the process (called as lasing) by which laser system converts electrical energy into a light of high intensity energy. The medium by which the lasing process carried out is called lasing medium. In any model of an atom, positively charged nucleus is surrounded by negatively charged electrons rotating at some specified path called orbits. The diameter and geometry of the orbit vary based on many parameters including number of electrons, surrounded magnetic field, structure of electrons and the existence of neighbor atoms. Every electron presents in the orbital connected with a distinctive energy level. An atom is said to be at ground level when it is at absolute zero temperature in which all the electrons reside in their lowest potential energy. Energy from any exciting sources such as electronic pulsation at higher temperature, chemical reaction or photon can be absorbed by an electron at ground level. After absorbing the energy, it excites to a higher energy level as schematically shown in **Figure 1**. Thus the movement of electron from lower to higher energy level is accomplished. Upon reaching higher energy levels, electron attains an unstable energy band. Immediately within very short time (tens of nanosecond) it starts moving back to ground state by releasing

**88**

**Figure 1.**

*Excitation between energy levels.*

a photon and this process is termed as "spontaneous emission." The frequency of emitted photon would be equal to the frequency of exciting photon.

Sometime, when the electrons put into a meta-stable band due to energy change, the electron stays in the higher energy level itself for a short time (micro to milliseconds). The state by which more number of electrons stays in meta-stable energy level compared to the atoms in the ground level of a material is called "population inversion." These electrons are stimulated by suitable energy or frequency photons to come back to ground state. Photons emission due to this stimulated return of electrons is termed as "stimulated emission." In this way, the emitted photons along with one original photon temporarily having some spatial phase would create coherent laser beam. From the schematic representation of stimulated absorption, spontaneous emission, and stimulated emission as shown in **Figure 2**, position of electrons in various energy levels are shown.

**Figure 2.** *Excitation between energy levels.*

**Figure 3.** *Excitation between energy levels.*

The working of laser is schematically represented in **Figure 3**. A lasing medium contained by a cylindrical glass container is closed using completely (100%) reflecting mirror on one end and partially reflecting mirror on the other end. When the glass vessel is exposed to a light using flash lamps, the photons of light excites the atoms of lasing medium thus population inversion is obtained. Further due to stimulated emission, photons are emitted. These stimulated photons in the longitudinal direction form a high intense, coherent and highly directional laser beam. Most of the stimulated photons would not be in the longitudinal direction and these photons usually generate waste heat and finally lost.
