**4. Types of laser**

Lasers are classified based on the state of lasing medium used and the temporal mode. Based on the physical nature lasers are classified into solid-state lasers, gas lasers, semiconductor, and liquid dye lasers [4]. Based on temporal mode, further laser is categorized into two modes namely continuous wave (CW) and pulsed mode. Continuous mode emits the laser beam continuously without interruption whereas pulsed mode emits the laser beam periodically. **Tables 1** and **2** shows the important laser types along with their wavelengths.

In solid-state layers, the lasing medium is doped with very small number of impurity ions. Maimam has developed the first solid-state laser during 1960 which was a ruby laser. There are a number of laser types developed in the solid-state category in which Nd:YAG is majorly used for LBM applications. Solid-state lasers such as Nd:YAG, ruby and Nd-glass are highly used for machining metallic materials. Nd:YAG lasers can also be used to ceramic materials. Gas lasers are grouped


**93**

*Laser Machining*

**Table 2.**

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

*Semiconductor and liquid dye lasers with their wavelengths.*

sometimes organic materials also.

**5. Material removal using laser**

setup is schematically shown in **Figure 8**.

**5.2 Mechanism of material removal in LBM**

effects of laser beam-work material interaction [5].

**5.1 Construction of LBM**

into three categories based on the composition such as neutral atom, ion, and molecular. Gas lasers generally can be of CW or pulsed mode lasers and available with axial flow, transverse flow and folded axial flow in construction. CO2 laser is the most commonly used gas laser for machining plastics, ceramics, nonmetals and

**Semiconductor lasers Liquid dye lasers Lasing medium Wavelength (nm) Lasing medium Wavelength (nm)** AlGaInP 630–680 Stilbene 403–428 AlGaAs 780–880 Coumarin 102 460–515 InGaAs 980 Rhodamine 6G 570–640 InGaAsP 1150–1650 — —

Semiconductor lasers, though made of solid materials the working principle are different from solid-state lasers. It is based on radiative recombination of charge carriers. Unique characteristic of a semiconductor laser is that they are capable of producing wide beam divergence angles around 40°. Comparing to other types of lasers, liquid-state lasers are easier to fabricate. Main advantages of liquid-state lasers are ease cooling and replenishment in laser cavities. Spectral properties of liquid organic molecules enable liquid dye lasers to get tuned within wide range of wavelengths from 200 nm to 1000 nm. The detailed working principles of these lasers are beyond the scope of this chapter and can be found in any standards texts.

Laser beam machining is a nonconventional, advanced machining process wherein there are essential parts required to construct a complete LBM setup. A pumping medium or lasing medium that contains large quantity of atoms is a primary component to produce laser light. For exciting the atoms in lasing medium, a flash lamp or flash tube is needed and it should be connected to the controlled high voltage power supply. Based on the type of operating mode (either pulsed mode or CW) a capacitor can be integrated to the power circuit. A typical solid-state LBM

Laser based machining processes is identified as a material removal technique in industrial application. Materials removal is accomplished by the interaction between the laser beam and work material. It is severely a localized thermal process. Higher amount of light energy is received by base material and then higher heat is created between the locality of interaction while hitting the laser source on the base material. Due to highly elevated temperature at the beam spot, the material becomes soft, melt, burn and vaporized. Additionally, the interaction of laser beams and work material is associated with the material removal by photochemical process which is often called photo ablation. **Figure 9** schematically represents the

#### **Table 1.**

*Solid-sate and gas lasers with their wavelengths.*


## **Table 2.**

*Practical Applications of Laser Ablation*

transmitted by normal light source and a laser [3].

important laser types along with their wavelengths.

machining applications.

**3.4 Intensive radiance**

**4. Types of laser**

from light source therefore certain amount of energy is lost. But laser beams possess very low-diffraction property hence higher energy transfer can be effectively achieved. This directional characteristic is useful when directing the laser beam for

The intensive radiance of a light is defined as the amount of power emitted per unit area for a given solid angle. The unit for radiance is watts per square meter per steradian. The angle by which a light beam is focused as a cone is called a solid angle. Since the intensity of photons is high in laser beam, it can have high output powers. Laser light source possess extreme amount of intensive radiance and transmitted through a small solid edge angle. This property makes it very convenient to be used for machining operations. **Figure 7** gives the comparison of power density

Lasers are classified based on the state of lasing medium used and the temporal mode. Based on the physical nature lasers are classified into solid-state lasers, gas lasers, semiconductor, and liquid dye lasers [4]. Based on temporal mode, further laser is categorized into two modes namely continuous wave (CW) and pulsed mode. Continuous mode emits the laser beam continuously without interruption whereas pulsed mode emits the laser beam periodically. **Tables 1** and **2** shows the

In solid-state layers, the lasing medium is doped with very small number of impurity ions. Maimam has developed the first solid-state laser during 1960 which was a ruby laser. There are a number of laser types developed in the solid-state category in which Nd:YAG is majorly used for LBM applications. Solid-state lasers such as Nd:YAG, ruby and Nd-glass are highly used for machining metallic materials. Nd:YAG lasers can also be used to ceramic materials. Gas lasers are grouped

**Solid-sate lasers. Gas lasers Lasing medium Wavelength (nm) Lasing medium Wavelength (nm)** Ruby 694 ArF 191 Alexandrite 700–820 KrF 249 Ti-sapphire 700–1100 XeCl 308 Nd-YLF 1047 XeF 351 Nd:YAG 1064 Argon 488, 514.5 Nd:glass 1062 Krypton 520–676 Er-YAG 2940 HeCd 441.5, 325 — — Copper vapor 510.6, 578.2

> Gold vapor 628 HeNe 632.8 CO2 10,600

**92**

**Table 1.**

*Solid-sate and gas lasers with their wavelengths.*

*Semiconductor and liquid dye lasers with their wavelengths.*

into three categories based on the composition such as neutral atom, ion, and molecular. Gas lasers generally can be of CW or pulsed mode lasers and available with axial flow, transverse flow and folded axial flow in construction. CO2 laser is the most commonly used gas laser for machining plastics, ceramics, nonmetals and sometimes organic materials also.

Semiconductor lasers, though made of solid materials the working principle are different from solid-state lasers. It is based on radiative recombination of charge carriers. Unique characteristic of a semiconductor laser is that they are capable of producing wide beam divergence angles around 40°. Comparing to other types of lasers, liquid-state lasers are easier to fabricate. Main advantages of liquid-state lasers are ease cooling and replenishment in laser cavities. Spectral properties of liquid organic molecules enable liquid dye lasers to get tuned within wide range of wavelengths from 200 nm to 1000 nm. The detailed working principles of these lasers are beyond the scope of this chapter and can be found in any standards texts.
