CNC Laser Engraving Machine by MNS Uet Multan

 

Table of Contents  Table of Contents .................................................................................................................................. .................................................................................................................................. 1 List of Figures: .............................................................. .................................................................................................................................... ........................................................................ .. 3 List of Tables: ...................................................................................................................................... ........................................................................................................................................ .. 5 Chapter Number 01 .............................................................................................................................. .............................................................................................................................. 6 .......................................................................................................................................... ........................... 6 Introduction ................................................................................................................

1.2 Aim: ............................................................... ..................................................................................................................................... ................................................................................... ............. 6 1.3 Objectives: ..................................................................................................................................... ....................................................................................................................................... .. 6 1.4 Problem Statement: ........................................................................................................................ ........................................................................................................................ 7 1.5 Scope: ............................................................................................................................... ............................................................................................................................................... ................ 7 1.6 Utilization of Project: ..................................................................................................................... ..................................................................................................................... 7 Chapter Number 02 .............................................................................................................................. .............................................................................................................................. 8 Literature Review ..................................................................... ................................................................................................................................. ............................................................ 8 2.1 History of LASER: ............................................................................................................. ......................................................................................................................... ............. 8 2.2 Working Principle: ............................................................ ......................................................................................................................... ............................................................. 9 2.2.1 Absorption of Radiation: ............................................................................................................. ............................................................................................................ 9 2.2.2 Spontaneous Emission: ................................................................................................................ ................................................................................................................ 9 2.2.3 Stimulated Emission: ................................................................................................................. ................................................................................................................. 10 2.3 Characteristics of LASER:. .......................................................................................................... .......................................................................................................... 11 2.3.1 Coherence: .................................................................................................................................. ..................................................................................................................................11 2.3.2 Directionality:. ............................................................................................................................ ............................................................................................................................ 12 2.3.3 Monochromatic: ......................................................................................................................... .........................................................................................................................12 2.3.4 High Intensity:. ........................................................................................................................... ........................................................................................................................... 13 2.4 Differences Between Ordinary Light and LASER Beam: .........................................................13 .................................................................................................................. ............................................... 13 2.5 LASER Construction: ................................................................... 2.5.1 Pump Source: ............................................................................................................................. ............................................................................................................................. 13

2.5.2 LASER Medium: ............................................................ ....................................................................................................................... ........................................................... 14 2.5.3 Optical Resonator: ..................................................................................................................... ..................................................................................................................... 14 2.6 Types of LASER: ............................................................... .......................................................................................................................... ........................................................... 14 2.6.1 Solid-State LASER: ................................................................................................................... ................................................................................................................... 15 2.6.2 Gas LASER: ............................................................................................................................... ............................................................................................................................... 15 2.6.3 Liquid LASER: ............................................................... .......................................................................................................................... ........................................................... 16 2.6.4 Semiconductor LASER: ............................................................................................................ ............................................................................................................ 16 2.7 Stepper Motor: .............................................................................................................................. .............................................................................................................................. 17 2.8 Stepper Motor Driver: .................................................................................................................. ................................................................................................................. 17 1|Page 

 

2.9 Arduino CNC Shield: ................................................................................................................... ................................................................................................................... 18 2.10 Arduino UNO: ............................................................................................................................. .............................................................................................................................18 2.11 LASER Diode Module: ...............................................................................................................19 2.12 Previous Working Models:. ......................................................................................... ....................................................................................................... .............. 19 2.13 Modification: ............................................................................................................................... ............................................................................................................................... 21 2.14 Advantages Over Previous Working Models: .......................................................................... .......................................................................... 22 Chapter Number 03 ............................................................................................................................ ............................................................................................................................ 23 Methodology ........................................................................................................................................ ........................................................................................................................................ 23 3.1 General Research Purpose: ..........................................................................................................23 3.2 Market Research ........................................................................................................................... ...........................................................................................................................24 3.3 Mechanical System: ...................................................................................................................... ...................................................................................................................... 24 3.4 Electrical System:. ......................................................................................................................... ......................................................................................................................... 24 3.4.1 Power Supply: ............................................................................................................................ ............................................................................................................................ 24 3.4.2 Stepper Motor Driver Board: ................................................................................................... ................................................................................................... 24 3.5 Software System: ................................................................................................................ .......................................................................................................................... ........... 24 .......................................................................................................................... 25 3.6 Structure Design: ..........................................................................................................................

3.7 Concept Sketches: .............................................................. ......................................................................................................................... ........................................................... 25 3.8 CAD Design: .................................................................................................................................. ..................................................................................................................................26 3.9 LASER Engraver Machine Parts CAD Model:  ......................................................................... ......................................................................... 27 3.10 LASER Engraver Machine Parts CAD Model with Dimensions: .......................................... 29 3.11 Assembling and Fabrication of CNC LASER Engraving Machine:  ...................................... 30 3.12 Bill of Materials: .............................................................. ......................................................................................................................... ........................................................... 30 3.13 Operating:. ................................................................................................................................... ................................................................................................................................... 39 3.14 Final Engraved Model: ...............................................................................................................42 3.15 Focusable 2Watt or 2000mWatt 405nm Infrared IR LASER ................................................ 43 43 3.15.1 LASER Description: ................................................................................................................ ................................................................................................................ 43 3.15.2 2-Watt LASER Description: ................................................................................................... ................................................................................................... 43 Chapter Number 04 ............................................................................................................................ ............................................................................................................................ 45 Results and Discussions ...................................................................................................................... ...................................................................................................................... 45 4.1 Test Runs with Parameters Changes: ................................................................... ......................................................................................... ...................... 45 Chapter Number 05 ............................................................................................................................ ............................................................................................................................ 51 Conclusions and Suggestions.............................................................. .............................................................................................................. ................................................ 51 5.1 Conclusions:............................................................. ................................................................................................................................... ...................................................................... 51 5.2 Future Studies: .............................................................................................................................. .............................................................................................................................. 51 ........................................................................................................................................... ..................................................................... 52 References:......................................................................

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List of Figures: Figure 2.1 Working principle of LASER ............................................................... ............................................................................................................ ............................................. 8  Figure 2.2 (a) Absorption, (b)Spontaneous emission & (c)Stimulated ( c)Stimulated emission, ............................................ 9  Figure 2.3 Absorption of radiation .............................................................. ...................................................................................................................... ........................................................ 9  Figure 2.4 Spontaneous emission ................................................................. ....................................................................................................................... ...................................................... 10  Figure 2.5 Stimulated emission .......................................................... ........................................................................................................................ ................................................................ .. 11  Figure 2.6 Incoherent light................................................................................................................................. 11  Figure 2.7 Coherent light waves ...................................................................................................................... ........................................................ ................................................................ .. 12  Figure 2.8 (a)Ordinary light and (b) LASER light .......................................................................................... .......................................................... ................................ 12  Figure 2.9 Monochromatic light ........................................................................................................................ ........................................................................................................... ............. 13  Figure 2.10 LASER construction ........................................................................... ...................................................................................................................... ........................................... 14  Figure 2.11 Solid state LASER .......................................................... ........................................................................................................................ ................................................................ .. 15  Figure 2.12 Gas LASER .......................................................... ........................................................................................................................ ........................................................................... ............. 16  Figure 2.13 Liquid LASER ..................................................................................... ................................................................................................................................ ........................................... 16  Figure 2.14 Semiconductor LASER ............................................................ .................................................................................................................. ...................................................... 17  Figure 2.15 Stepper motor ................................................................................................................................. ................................................................................................ ................................. 17  Figure 2.16 Stepper motor driver ................................................................ ...................................................................................................................... ...................................................... 18  Figure 2.17 Arduino CNC shield ....................................................................................................................... ................................................................................................ ....................... 18  Figure 2.18 Arduino UNO ................................................................................................................................ ................................................................. ................................................................. .. 18  Figure 2.19 LASER diode module ..................................................................................................................... ............................................................... ...................................................... 19  Figure 2.20 CNC LASER engraver machine ................................................................................................... ................................................................ ................................... 20  Figure 2.21 CNC LASER cutter machine......................................................................................................... machine................................................... ...................................................... 20  Figure 2.22 CNC LASER cutting machine m achine ............................................................ ....................................................................................................... ........................................... 21  Figure 2.23 3-Axis 3 -Axis Computer Numerical Control (CNC) LASER cutter ...................................................... 21  Figure 3.1 Methodology ..................................................................................................................................... 23  Figure 3.2 Structure design .............................................................................................................................. ................................................................ ................................................................ .. 25  Figure 3.3 Concept sketches front view ....................................................................................... ............................................................................................................ ..................... 25  Figure 3.4 Concept sketches top view .................................................................... ............................................................................................................... ........................................... 26  Figure 3.5 Holding plate & foot’s ................................................................ ...................................................................................................................... ...................................................... 26  Figure 3.6 Orthographic view our machine model .......................................................................................... 26  Figure 3.7 CAD Design front view .................................................................................................................. ................................................... ................................................................. .. 27  Figure 3.8 CAD Design left side view ................................................................................................................ .......................................................... ...................................................... 27  Figure 3.9 CAD Design top view........................................................................................................... view............................................. ........................................................................... ............. 27  Figure 3.10 CAD Design LASER....................................................................................................................... LASER................................................................. ...................................................... 28  Figure 3.11 CAD Design stepper motor ............................................................................................................ 28  Figure 3.12 Holding stand which hold stepper motor window wheels and allow motion............................. mot ion............................. 28  Figure 3.13 Holding stand LASER and stepper motor ................................................................................... ................................................... ................................ 28  Figure 3.14 Aluminium channel ........................................................................................................................ ................................................................................................ ........................ 29  Figure 3.15 Aluminium channel dimensions .................................................................................................. .................................................................................................... .. 29  Figure 3.16 Holding stand which hold LASER ................................................................................................ 29  Figure 3.17 CAD drawing on drawing sheet .................................................................................................... ....................................................................................... ............. 30  Figure 3.18 CNC LASER engraver machine parts .......................................................... .......................................................................................... ................................ 30  Figure 3.19 L Key Bolt for fix machine foots f oots ................................................................................................... ................................................................................................. .. 31  Figure 3.20 L Joints for fix frame ................................................................................................ ............................... ...................................................................................... ..................... 31  Figure 3.21 Foots of CNC machine ................................................................................................................... ............................................................. ...................................................... 32  Figure 3.22 Frame Fram e parts ........................................................................................................................ .......................................................... ........................................................................... ............. 32  Figure 3.23 Frame assembled ............................................................................................................................ ................................................................................. ........................................... 32  Figure 3.24 Frame with foots assembled ................................................................................................ ............................... ........................................................................... .......... 33  Figure 3.25 Moving mechanism ......................................................... ....................................................................................................................... ................................................................ .. 33  Figure 3.26 Assembled moving mechanism (inner view) ........................................................... ................................................................................ ..................... 33  Figure 3.27 Assembled moving mechanism (outer view) ................................................................................ 34  Figure 3.28 Left & Right assembled moving mechanism (inner view) .......................................................... ............... ........................................... 34  Figure 3.29 Left & Right assembled moving mechanism (outer view) .......................................................... ............... ........................................... 34  Figure 3.30 Moving mechanism of laser ................................................................ ........................................................................................................... ........................................... 35  Figure 3.31 Assembled moving mechanism ........................................................... ...................................................................................................... ........................................... 35 

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Figure 3.32 Fitting Fit ting moving mechanism on aluminium channel ...................................................................... ............................................................ .......... 35  Figure 3.35 Fitting moving mechanism of aluminium channel............................................................. channel ....................................................................... .......... 36  Figure 3.36 Fitting of LASER moving mechanism on main frame ................................................................ 36  Figure 3.37 GT 2 Belt for moving mechanism .................................................................................... ...................... ........................................................................... ............. 36  Figure 3.38 Electronics components for LASER ............................................................................................. 37  Figure 3.39 Assembled electronic components for LASER .......................................................................... ............................................................................ .. 37  Figure 3.40 Belt fitting of CNC LASER engraver machine ............................................................................ 37  Figure 3.41 Belts fitted for moving mechanism of machine ............................................................................ ................................................................ ............ 38  Figure 3.42 Control box for CNC LASER engraver machine ........................................................................ 38  Figure 3.43 CNC LASER engraver machine wiring ....................................................................................... ................................................................ ....................... 38  Figure 3.44 CNC LASER Engraver Machine .................................................................................................. .......................................................................... ........................ 39  Figure 3.45 Testing # 1 ....................................................................................................................................... ................................................................................. ...................................................... 39  Figure 3.46 Testing # 2 ....................................................................................................................................... ................................................................................. ...................................................... 39  Figure 3.47 Starting software ............................................................................................................................ ...................................................................... ...................................................... 40  Figure 3.48 Selection of picture ................................................................................................. ......................................................................................................................... ........................ 40  Figure 3.49 Size setting ............................................................ ............................................................................................................................. ........................................................................... .......... 41  Figure 3.50 Tracing image ................................................................................................................................. ......................................................................................................... ........................ 41  Figure 3.51 Tracing image ................................................................................................................................. ......................................................................................................... ........................ 41  Figure 3.52 After tracing image......................................................................................................................... 42  Figure 3.53 Parameters setting .......................................................... ........................................................................................................................ ................................................................ .. 42  Figure 3.54 Final engraved model ............................................................... ..................................................................................................................... ...................................................... 42  Figure 3.55 2-Watt Diode type LASER ................................................................................................ ................................ ............................................................................ ............ 43  Figure 3.56 Final year project CNC LASER engraver machine .................................................................... 44  Figure 4.1 Test run max power 50 %, speed 2000 mm/min, 500 line per inch and line interval 0.051 ....... 46  Figure 4.2 Test run max power 50 %, speed 1500 mm/min, 500 line per inch and line interval 0.051 ....... 46  Figure 4.3 Test run max power 50 %, speed 1000 mm/min, 500 line per inch and line interval 0.051 ....... 46  Figure 4.4 Test run max power 50 %, speed 2000 mm/min, 2 250 50 line per inch and line interval 0.102 ....... 46  Figure 4.5 Test run max power 50 %, speed 1500 mm/min, 250 line per inch and line interval 0.102 ....... 47  Figure 4.6 Test run max power 50 %, speed 1000 mm/min, 250 line per inch and line interval 0.102 ....... 47  Figure 4.7 Test run max power 50 %, speed 1000 mm/min, 1 100 00 line per inch and line interval 0. 0.254 254 ....... 47  Figure 4.8 Test run max power 50 %, speed 1500 mm/min, 1 100 00 line per inch and line interval 0. 0.254 254 ....... 47  Figure 4.9 Test run max power 50 %, speed 2000 mm/min, 1 100 00 line per inch and line interval 0. 0.254 254 ....... 47  Figure 4.10 Test run max power 75 %, speed 2000 mm/min, 100 line per inch and line interval 0.254 ..... 47  Figure 4.11 Test run max power 75 %, speed 1500 mm/min, 100 line per inch and line interval 0.254 ..... 48  Figure 4.12 Test run max power 75 %, speed 1000 mm/min, 100 line per inch and line interval 0.254 ..... 48  Figure 4.13 Test run max power 100 %, speed 1000 mm/min, 500 line per inch and line interval 0.051 ... 48  Figure 4.14 Test run max power 100%, speed 1500 mm/min, 1000 line per inch and line interval 0.025 .. 48  Figure 4.15 Sample no 1 ............................................................................................................. ..................................................................................................................................... ........................ 48  Figure 4.16 Sample no 2 ............................................................................................................. ..................................................................................................................................... ........................ 49  Figure 4.17 Sample no 3 ............................................................................................................. ..................................................................................................................................... ........................ 49  Figure 4.18 MNS UET MULTAN ..................................................................................................................... .......................................................................... ........................................... 49  Figure 4.19 Prof Dr Aamir Ijaz engraved picture ................................................................... ........................................................................................... ........................ 49  Figure 4.20 Engraved image of prof. Dr. Syed Mansoor Sarwar ................................................................... 50 

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List of Tables:  Table 2.1 Differences between ordinary light and LASER beam ...................................................... ................................................................... ............. 13  Table 3.1 Bill of materials .................................................................................................................................. 30  Table 4.1 Test runs with parameters changes .................................................................................................. ....................................................... ........................................... 45 

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Chapter Number 01 Introduction 1.1 Background: With the deveopment of new technological and economic needs, new industrial requirements such as high precision, good quality, high production rates and low production costs are increasingly demanded. Most of such requirements, including dimensional accuracy, conformance to tolerances of finished products and production rate can be met with better machine tools. With the help of CNC technology, machine tools today are not limited to human capabilities but are able to make ultra-precision products down to nano scales in a much faster manner .  The traditional design philosophy of machine tools is multi-functionality and highest  precision possible. However, with the dramatic increase of industry variet varieties ies and the growing demand of miniature products, these general-purpose machine tools are not efficient, either in terms of machining time or cost, in manufacturing products with special sizes and precision requirements. There are several advantages of using small machines to produce small sized objects. With a smaller machine size, space is saved. The energy required to operate the machine is reduced as well. It now requires less material mate rial and components to make the machine, hence bringing down the cost greatly. The weight of moving component also comes down so that during operation, the vibration and noise, as well as pollution to the environment, are markedly reduced. As the machine becomes denser and lighter, it becomes more portable. The layout of the manufacturing plant can be more flexible f lexible & productivity and manufacturing speed also increases due to operations. In modern CNC systems, end-to-end component design is highly automated using Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) programs. The  programs produce produce a computer file that is interpreted to extract the commands needed to operate a particular machine via a post processor, and then loaded into the CNC machines for  production. Any particular particul ar component might require the use of a number of different tools  –   drills, saws, etc., modern machines often combine multiple tools into a single "cell". In other installations, several different machines are used with an external controller and human or robotic operators that move the component from machine to machine. In either eit her case, the series of steps needed to produce any part is highly automated and produces a part that matches the original CAD design as per acceptable tolerances.

1.2 Aim: The aim of this project is to develop an economical working model of two axis CNC LASER Engraving Machine, which is portable and suitable for small scale work.

1.3 Objectives:   To design the economical working model of CNC LASER engraving machine.

▪

  To develop a portable light weight structure which will be easy to handle and transport.  

▪

  To develop the model according to design. 

▪

  To reduce the large-scale industrial Engraving machine to a small portable lab

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1.4 Problem Statement: We describes the design of a small two (2) axis CNC LASER Engraver Engraver Machine, monitoring and controlling system based on stepper motor using Arduino and belt and pulley mechanism. Some of the previous systems used three dimensional CNC machines to design, milling and drilling etc. The biggest drawback of these systems was complexity, costly and high weight of model. To overcome these problems, we proposed an idea ide a of designing two axis CNC LASER Engraver Engraver Machine which has low weight as compared to previous one. In o our ur system we have to give instructions through the software which is installed in laptop and it contains G code to CNC router via Microcontroller Arduino then signals applied to stepper motor driver and according to changes in position and location as per the commands LASER starts to engrave the images on given object, and LASER module is operated by LASER driver. The object may be all non- Metallic materials like wood, foam, plastic, rubber, paper.

1.5 Scope: Total project work is divided into three phases. First is the CNC LASER Engraving Machine structure. This machine operates in 2-axis which is in x-axis and y-axis. Besides, the machine uses belt and pully concept. Next, the software that suitable and capable for this machine is  is LIGHTBURN.The third one which is the important ones is the Engraving process. From this Engraving process, a conclusion can be made about the Engraving performance and cut quality. However, from this LASER Engraving process, there are several operating  parameters that should find in order to get the great cutting and Engraving Engraving performances.

1.6 Utilization of Project: LASER engraving is the process of removing a portion of material to leave an engraved mark which is visible beneath. The engraving process is produced by the LASER beam removing material to create a mark, where the LASER acts like a chisel and blows away selected areas of the subject material. The depth of the engraving made will depend on the dwell time as well as the type of material being used. It can be used on a variety of materials, including plastics, wood , Acrylic sheet, leather, fabrics f abrics and cutting paper or card board.Use as a lab equipment in department lab.

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Chapter Number 02 Literature Review In this chapter details over view of LASER and its types. The fundamental of LASER, history of LASER and the working principle of LASER is discussed. Besides, this reports also shows the view of the main point which is the LASER CNC Machine and the operating  parameters to make the engraving performances better.

2.1 History of LASER: The formation of LASER (Light Amplification by Stimulated Emission of Radiation), even 100 years ago starting from new reveal of LASER, LASER become one of the most  powerful engineering devices nowadays. In 1905, Max Plant gives the new information or theory about the relationship between the energy and frequency of radiation. His theory  becomes a starting point the LASER discovered and will encourage coming comi ng up physicists to find the new useful theory. In 1905, a famous physicist, Albert Einstein released his research about the photoelectric effect which proposed the light deliver in energy. Based on physic context, Albert Einstein says that discrete quantum particles that now we called as a photon. After two years, Albert Einstein become innovative by possible the process of LASER that mentioned earlier which is stimulated emission. LASER a devicenot that amplifies or increases thethe intensity of of light and produces highly directional light.isLASER only amplifies or increases intensity light but also generates the light. LASER emits light through a process called stimulated emission of radiation which amplifies or increases the intensity of light. Some LASER generates visible light but others generate ultraviolet or infrared rays which are invisible. In general, when electron jumps from a higher energy level to a lower energy level, it emits light or photon. The energy of the emitted  photon is equal equal to the energy difference between the energy levels. The The loss of electron energy is attributed to the entire atom. Therefore, it can be thought that the atom is moving from a higher energy state to a lower energy state. LASER light is different from the conventional light. LASER light has extra-ordinary properties which are not present in the ordinary light sources like sun and incandescent lamp. The conventional light sources such as electric bulb or tube light does not emit highly directional and coherent light whereas LASER produce highly directional, monochromatic, coherent and polarized light beam. In conventional light sources, excited electrons emit light at different times and in different directions so there is no  phase relation between the emitted photons. On the other hand, the photons emitted by the electrons of LASER are in same phase and move in the same direction.[1]

Figure 2.1 Working principle of LASER  

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2.2 Working Principle: The principles of LASER are divided into three divisions and sections.

  Absorption of radiation   Spontaneous emission

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  Stimulated emission 

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Figure 2.2 (a) Absorption, (b)Spontaneous emission & (c)Stimulated emission,

2.2.1 Absorption of Radiation:

Absorption of radiation is the process by which electrons in the ground state absorbs energy from photons to jump into the higher energy level. The electrons orbiting very close to the nucleus are at the lower energy level or lower energy state whereas the electrons orbiting farther away from the nucleus are at the higher energy level. The electrons in the lower energy level need some extra energy to jump into the higher energy level. This extra energy is provided from various energy sources such as heat, electric electri c field, or light. In general, the electr electrons ons in the lower energy state cannot jump into the higher energy state. They need sufficient energy in order jump into the higher energy state.[1]

Figure 2.3 Absorption of radiation  

2.2.2 Spontaneous Emission: Spontaneous emission is the process by which electrons in the excited state return to the ground state by emitting photons. The electrons in the excited state s tate can stay only for a short  period. The time up to which which an excited electron can stay at higher energy state (E2) is known as the lifetime of excited electrons. The lifetime of electrons in excited state is 10-8 second. 9|Page 

 

 

Thus, after the short lifetime of the excited electrons, they return to the lower energy state or ground state by releasing energy in the form of photons. In spontaneous emission, the electrons move naturally or spontaneously from one state (higher energy state) to another state stat e (lower energy state) so the emission of photons also occurs naturally.[1]  

Figure 2.4 Spontaneous emission

2.2.3 Stimulated Emission: Stimulated emission is the process by which incident photon interacts with the excited electron and forces it to return to the ground state. In stimulated emission, the light energy is supplied excited electron instead of supplying light energy the ground state electrons.directly Unlike to thethe spontaneous emission, the stimulated emission is not atonatural process it is an artificial process. In spontaneous emission, the electrons in the excited state will remain there until its lifetime is over. After completing their lifetime, they return to the ground state  by releasing energy in the form of light. However, in stimulated emission, emiss ion, the electrons in the excited state need not wait for completion of their lifetime. An alternative technique is used to forcefully return the excited electron to ground state before completion of their lifetime. This technique is known as the stimulated emission. When incident photon interacts with the excited electron, it forces the excited exci ted electron to return to the ground state. This excited electron ele ctron release energy in the form of light while falling to the ground state. In stimulated emission, two photons are emitted (one additional photon is emitted), one is due to the incident photon and another one is due to the energy release of excited electron. Thus, two photons are emitted. The stimulated emission process is very fast f ast compared to the spontaneous emission process. All the emitted photons in stimulated emission have the same energy, same frequency and are in phase. Therefore, all photons in the stimulated emission travel in the same direction. The number of  photons emitted in the stimulated emission emiss ion depends on the number of electrons in i n the higher energy level or excited state and the incident light intensity. It can be written as: Number of emitted photons α Number of electrons in the excited state + incident light intensity.[1]  

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Figure 2.5 Stimulated emission

2.3 Characteristics of LASER: LASER light has four unique characteristics that differentiate it from ordinary light: these are[1]

       

▪ ▪ ▪ ▪

Coherence Directionality Monochromatic High intensity

2.3.1 Coherence: We know that visible light is emitted when excited electrons (electrons in higher energy level) jumped into the lower energy level (ground state). The process of electrons moving from higher energy level to lower energy level or lower energy level to higher energy level is called c alled electron transition. In ordinary light sources (lamp, sodium lamp and torch light), the electron transition occurs naturally. In other words, electron transition in ordinary light sources is random in time. The photons emitted from ordinary light sources have different energies, frequencies, wavelengths, or colors. Hence, the t he light waves of ordinary light ssources ources have many wavelengths. Therefore, photons emitted by an ordinary light source are out of phase.[1]

Figure 2.6 Incoherent light 

In LASER, the electron transition occurs artificially. In other words, in LASER, electron transition occurs in specific time. All the photons emitted in LASER have the same energy, frequency, or wavelength. Hence, the light waves of LASER light have single wavelength or color. Therefore, the wavelengths of the LASER light are in phase in space and time. In LASER, a technique called stimulated emission is used to produce light. Thus, light generated by LASER is highly coherent. Because of this coherence, a large amount of power can be concentrated in a narrow space. 11 | P a g e  

 

 

Figure 2.7 Coherent light waves  

2.3.2 Directionalit Directionality: y: In conventional light sources (lamp, sodium lamp and torchlight), photons will travel in random direction. Therefore, these light sources emit light in all directions. On the other hand, in LASER, all photons will travel in same direction. Therefore, LASER emits light only in one direction. This is called directionality of LASER light. The width of a LASER beam is extremely narrow. Hence, a LASER beam can travel to long distances without spreading.[1]

Figure 2.8 (a)Ordinary light and (b) LASER light

If an ordinary light travels a distance of 2 km, it spreads to about 2 km in diameter. On the other hand, if a LASER light travels a distance of 2 km, it spreads to a diameter less than 2 cm.[1]

2.3.3 Monochromatic: Monochromatic light means a light containing a single colour or wavelength. The  photons emitted from from ordinary light sources have different energies, frequencies, wavelengths, or colours. Hence, the light waves of ordinary light sources have many wavelengths wavel engths or colours. Therefore, ordinary light is a mixture of waves having different frequencies or wavelengths. On the other hand, in LASER, all the emitted photons have the same energy, frequency, or wavelength. Hence, the light waves of LASER have single wavelength or colour. Therefore, LASER light covers a very narrow range of frequencies or wavelengths.[1]

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Figure 2.9 Monochromatic light 

2.3.4 High Intensity: You know that the intensity of a wave is the energy per unit time flowing through a unit normal area. In an ordinary light source, the light spreads out uniformly in all directions. If you look at a 100-Watt lamp filament from a distance of 30 cm, the power entering your eye is less than 1/1000 of a watt. In LASER, the light spreads in small region of space and in a small wavelength range. Hence, LASER light has greater intensity when compared to the ordinary light If you look directly along the beam from a LASER (caution: don’t do it), then all the  power in the LASER would enter your eye. Thus, even a 1-Watt LASER would appear many thousand times more intense than 100-Watt ordinary lamp. Thus, these four properties of LASER beam enable us to cut a huge block of steel by melting. They are also used for recording r ecording and reproducing large information on a compact disc (CD).[1]

2.4 Differences Between Ordinary Light and LASER Beam:

Differences between ordinary light and LASER beam shown in table 2.1

Table 2.1 Differences between ordinary light and LASER beam

Sr No

1 2 3 4 5 6

Ordinary Light In ordinary light the angular spread is more. They are not directional. It is less intense. It is not a coherent beam and is not in phase. The radiation is polychromatic. Sun light, Mercury vapor lamp

LASER Beam In LASER beam the angular spread is less They are highly directional. It is highly intense. It is a coherent beam and is in phase. The radiations are monochromatic. He- Ne LASER, Co2 LASER

2.5 LASER Construction: LASER system consists of three important components:

  Pump source   LASER medium   Optical resonator

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2.5.1 Pump Source: The pump source or energy source is the part of a LASER system that provides energy to the LASER medium. To get LASER emission, emissi on, first we need to produce population inversion. Population inversion is the process of achieving greater number of electrons in higher energy state as compared to the lower energy state. The source of energy supplies sufficient amount of energy to the LASER medium by which the electrons in the lower energy state are excited to the higher energy state. As a result, population inversion can be achieved in the active medium or LASER medium. medium. The type of energy source used used is mostly depends on the LASER medium. Excimer LASER uses chemical reaction as energy source, a helium LASER uses an 13 | P a g e  

 

 

electric discharge as energy source and Nd: YAG LASER uses light focused from diode LASER as energy source. [1]

Figure 2.10 LASER construction

2.5.2 LASER Medium: The LASER medium is a medium where spontaneous and stimulated emission of radiation takes place. Generally, the population of lower energy state sta te is greater than the higher energy state. However, after achieving population inversion, the population of higher energy state becomes greater than the lower energy state. After receiving sufficient energy from source, the electrons in the lower energy state or ground state are excited to the higher energy state (in the LASER medium). light amplification is achieved in LASER medium. LASER medium is also known as active medium or gain medium. The LASER medium will determine the characteristics of the LASER light emitted. The LASER medium can be solid, liquid, or gaseous. Ruby LASER is an example for solid-state LASER. In this, a ruby crystal is used as an active medium. In this LASER, xenon discharge tube which provides a flash light acts as  pump source. Helium –  Helium –  Neon  Neon LASER is an example for gaseous LASER. In this, neon is used as an active medium. In this LASER, radio frequency (RF) generator acts as pump source.[1]

2.5.3 Optical Resonator: The LASER medium is surrounded by two parallel mirrors which provides feedback of the light. One mirror is fully reflective (100 % reflective) whereas another one is partially reflective (