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nd:yag laser energy level diagram

Those used for welding are protected by substantial and robust sheathing, which includes a flexible steel tube and nylon jacket, as shown in Fig. The focused spot size is determined by the laser beam diameters, the focal length of the focusing optics used, the beam mode and the beam divergence angle (The divergence angle is the angle at which the almost parallel laser beam propagates on leaving the laser). Nd:YAG, liquid dyes, gases like CO2 or Helium/Neon, or semiconductors such as GaAs. Your email address will not be published. The optical fibre material is SiO2 (quartz) and is generally less than 1 mm in diameter. * How does Nd:YAG laser work? The energy state E3 is the metastable state and exhibits longer lifespan. ND YAG laser working diagram. The incident beam diameter, Fig. This laser generally emits light of wavelength of nearly 1.064 μm. So, for lasing action to take place an external pump source is required. Thus, electrons present in E2 state will come to E1 without radiating energy in the form of a photon. Establishing Conditions for Nd: YAG Lasers: Keyhole welding is usually not possible with Nd: YAG lasers with output power below 500 W. At low average powers (400W) and the related pulse timing of 4-8 m sec, the penetration depth is usually limited to the size of spot diameter which is of the order of 0.5—1 mm. However, initially, electrons in E1 is very much higher as compared to E4. The output characteristics of the two are different while the construction and function of all solid state lasers is same. While down ward transition shows the emission of energy / light or lasing present in the Neon atom only. Reasons for using Nd: YAG Laser in medical field • It has very high depth of penetration in tissues (>5 mm) • Can be used as an endoscopic laser because the laser … The common shielding gases used for laser welding are argon, CO2, helium and OFN (oxygen-free nitrogen). An unfocused high power laser beam of several mm diameter if incident on the body could maim one for life. Generally, the total loss of laser power for an Nd:YAG laser and fibre optic system is no more than 10— 15%. TOS 7. There is a trend in weld shape formation which occurs as pulse width and repetition rate are adjusted in relation to laser power, as shown in Fig. Conventional Nd:YAG lasers pumped at 808nm suffer from heat-related processes, arising from the quantum defect between the pump energy level 4F 5/2 and emitting energy level 4F 3/2, such as strong thermal lensing, which can lead to beam quality degradation, pump-induced stresses, which Nd:YAG laser is basically categorized into 3 domains that are the active medium, pumping source and the optical resonator. Energy diagram: The simplified energy level diagram of chromium ions in a ruby laser, indicating appropriate excitation an decay is shown in Fig. These lasers operate in both pulsed and continuous mode. Three level laser energy diagram. Figure 10. Lamp pumping is possible due to the broadband pump absorption mainly in the 800-nm region and the four-level characteristics. 8 Fig. Continuous oscillation is possible with YAG. These energy levels are those of Neodymium (Nd3+) ions. Co-axial nozzle shielding device, shown in Fig. Major components of a resonator. It is a solid state and 4 level system as it consists of 4 energy levels. 14.39, without a significant loss of power. Use the above diagram to explain power losses in the laser. 1.4. 3. Simplified energy level diagram of the 4 F 3 / 2---4I 11 /2 laser transition in Nd:YAG showing the four- level nature of the system Because the laser light from Nd:YAG or CO2 laser is invisible to the human eye and it travels at extremely high speed of about 300,000 km/sec therefore any escaping reflected laser beam will strike instantaneously anyone in its path causing serious skin burns. Fig. However, one end is completely coated with silver so as to achieve maximum light reflection. Here, only those are shown which are significant for optical pumping with laser diodes and which are important for the laser process. The fibre optic beam delivery systems are by far the most simple and versatile. 14.34. It is possible that a laser cavity with an optical or lasing medium fault may produce the required laser power but with a distorted or different beam mode structure, thus affecting the focus spot size and consequently the welding power density. 4. It is a 4 level systems i.e. This type of laser also finds its application in medical field for the surgical purpose. Owing to high risk of serious eye damage from a Nd: YAG laser, instead of a viewing window a close-circuit television system is best suited for viewing the welding operation; with the correct camera and filters close-up observations can be made in absolute safety. Moreover, the laser can be positioned some distance from the production line and laser beam piped to it. Thus the beam splitting system, in conjunction with a fibre optic beam delivery system, can make several welds simultaneously at one or more work stations. The optical fibre assemblies used to transmit laser welding powers are purpose-made and quite different from those used in electronics. Energy level diagram: ! A 0.5 mm diameter SiO2fibre has an allowable bending radius of approximately 100 mm before efficiency is impaired, whereas for a 1 mm diameter fibre the safe radius is at least twice as large. However, a focused beam expands much faster beyond the focus point generally reaching a safe diameter after a few metres. Helium Neon Laser Energy Level Diagram Here upward transition shows the absorption of energy from the pumping source by Helium atom. Figure E1 locates the energy levels by wavenumberexpressed by convention in cm-1. Working of Nd:YAG laser. A helium–neon (HeNe) laser uses an electrical discharge in the helium-neon gas mixture, a Nd:YAG laser uses either light focused from a xenon flash lamp or diode lasers, and excimer lasers use a chemical reaction. 1. The four energy levels designated E0 to E3 and a laser transition of Nd3+ ions are shown in Fig. So, when external energy is provided in the active medium of the laser. 5.3. The figure below shows the road like the structure of Yd:YAG laser: Active medium: This is also known as the laser medium and is the middle portion of the structure i.e., Nd:YAG crystal. The most useful industrial laser for welding and cutting is the CO 2 laser in which the lasing medium is a mixture of carbon dioxide, nitrogen and helium in a typical ratio of 1: 1: 10 at a pressure of 20-10 torr with an electrical discharge of 10-30,000 volts.. A shielding gas is used in laser welding to protect the molten metal from oxidation and to protect the transmission of the laser beam as it comes to focus on the work that ensures good penetration by minimising beam expansion and scattering which may be caused by vapours and gases around the weld keyhole. When the rod temperature is low, these transitions will occur at a high rate. Metallurgy, Welding Processes, Laser Welding, Nd:YAG Laser. 14.36 The basic sheet metal joint configurations that can be laser welded. Although focused spot diameter is an important parameter but from a practical stand point the focusing off number is more useful to establish tolerant welding conditions where f number is defined as a ratio of focal length of the focusing optics (F) to the laser beam diameter (D), i.e.. Also included is a discussion of the second, third and fourth harmonic laser output gener-ated by the system. Quite often, however, satisfactory single spot welds can be made with Nd:YAG laser with no shielding gas at all because the weld is molten for too short a time to cause oxidising damage to result. Difference Between Valence Band and Conduction Band, Ward Leonard Method Of Speed Control Or Armature Voltage Control, Power Flow Diagram of DC Generator and DC Motor, Difference Between Electricity and Magnetism, Two Wattmeter Method of Power Measurement, Difference Between Refrigeration and Air Conditioning, Difference Between Conduction and Convection, Difference Between Circuit Switching and Packet Switching, Difference Between Static and Kinetic Friction, Difference Between Ductility and Malleability, Difference Between Physical and Chemical Change, Difference Between Alpha, Beta and Gamma Particles, Difference Between Electrolytes and Nonelectrolytes, Difference Between Electromagnetic Wave and Matter Wave. In this way, several electrons on stimulation produce photons thereby generating a coherent laser beam of 1.064 µm. Fabry-Perot resonator. Figure 2.18 shows the energy level diagram for Nd: YAG laser. The laser rod is an Yttrium aluminium garnet (YAG) consisting of Y3A15O12 isometric crystal implanted with carefully distributed 1 % neodymium (Nd) ions. For Nd: YAG laser welding a simple side tube shielding device, as shown in Fig. The multi-mode beam from an Nd: YAG laser can be split, Fig. After reading this article you will learn about the structure of Nd: YAG laser with the help of suitable diagrams. The ability to control to the current pulse parameters allow the control of weld penetration depth, profile and appearance. ; it contains 4 energy levels. The high power (> 800 W) Nd:YAG lasers with pulse time of say 2 m see and high pulse repetition frequency of 500 Hz it can produce keyhole type of welds with high aspect ratio of depth lo width. Privacy Policy 8. The average power density across the diameters is in the order of 6 to 13 W/mm2; the actual concentration of power being distributed according to the beam mode (see Fig. Though this laser also is a four level laser with Nd 3+ as the active laser ion, it cannot generate output at high repetition rate due to its very low thermal conductivity, but it can produce much higher energy output as compared to Nd:YAG laser. Such a device can be used to check beam characteristics during the welding operation and thus provide a method of quality assurance with respect to the laser beam. 5.1. will suffice for a laser up to 3 kW capacity. The laser active ions are pumped from the Z 1 sublevel of the 4 I 9/2 ground-state level to the 4 F 5/2 level, and then relax to the 4 F 3/2 upper lasing level with heat generation. Construction and working of Nd YAG laser - Duration: ... winnerscience 54,739 views. 14.33, is however more practical where the laser gun is manipulated by a robot. Due to doping, yttrium ions get replaced by the Nd3+ ions. It is a 4 level systems i.e. 14.35 while Fig. The Nd:YAG rod and the flash tube are placed inside an elliptical cavity so, that maximum produced light can reach the rod. When the krypton flash lamp is switched on, by the absorption of … The figure below shows the 4 state energy level diagram of Nd:YAG laser: Here, E1 is the lowest energy state while E4 is the highest energy level. When making continuous seam and butt welds an annular skirt shield co-axial with the laser beam, shown in Fig. Nd:YAG, a four-level system, to keep the lower laser level depopulated. For the transition from energy level 4I 9/2 to 4F 5/3 energy level. Then the electrons present in the energy state E1 gains energy and moves to energy state E4. 14.21, Nd: YAG laser welding can be applied to most of the basic joint configurations in plates and pipes, as shown in Fig. The precise distance depends on the focus f number; the lower the number the greater the rate of beam expansion. For example a gas (low rate of 10 to 20 lit/min. Nd: YAG laser is a four-level laser system, which means that the four energy levels are involved in laser action. Flash and arc lamps or diode lasers are used as the Optical pumping source. 14.36 shows the basic sheet metal joints which can be laser welded. When light is focused, the rays converge to a very small waist diameter, d, and length, L, Fig. Even if the concentration of Nd3+ ions in crystal increases, the spectrum of the oscillating light docs not become broad, because the valency and ion radius of Nd3+ are not much different from those of Y3+. Consider a ruby laser medium consisting of three energy levels E 1, E 2, E 3 with N number of electrons. Basically, as a source of optical pumping, xenon or krypton flash tube is taken in its case. 2. APPLICATIONS • Used widely in medical field. When using a correctly positioned coaxial or side tube shielding device. Required fields are marked *. Basically when the external energy source is provided then the electrons from lower energy state moves to higher energy state thereby causing lasing action to take place. External Energy source: Due to the difference in the energy levels, the electrons need some external pumping in order to perform a transition from one state to another. Such joints lend themselves to precision equipment and machine tool fabrication and if carefully applied, together with the low distortion offered by laser welding, can keep post-weld machining allowance to minimum. A simplified energy-level scheme for Nd:YAG is shown in Fig. a telescope in reverse). This is due to the fact that short wave length of 1.06 mm from Nd: YAG laser can be transmitted through a fibre optic with very little loss of power. The λ=1.06 μm laser transition is the strongest of the 4F 3 /2 →4I 11 /2 transitions. 3. However, care should be taken when using short pulses (< 1 m see) and high power (say 1 kW) as weld undercutting can occur through excessive vaporisation and material ejection. It is reported that a continuous weld of 0.5 mm depth can be achieved at a welding speed of more than 3 m/min. 3. Nd: YAG laser generates laser light commonly in the near-infrared region of the spectrum at 1064 nanometers (nm). 2. For keyhole welding by laser beam power densities of the order of 103 to 105 W/mm2 are required necessitating the focusing of laser beam to a very small spot of only a fraction of mm in diameter. Save my name, email, and website in this browser for the next time I comment. This makes Nd:YAG laser ideally suited to production automation. Your email address will not be published. Explain the construction and working of He-Ne lasers with a suitable energy level diagram. Table 1 illustrates various types of material currently used for lasing and the wavelengths that are emitted by that type of laser. Maximum light is pumped into the laser rod with the help of reflector assembly thus exciting the Nd ions to produce laser beam by spontaneous and stimulated emission. Prohibited Content 3. Nd : YAG LASER Diagram Non radioactive decay Laser 1.064μm Non radioactive decay E3 E2 E 4 E1 E0 Nd Energy Level Diagram of Nd : YAG laser E1, E2, E3 – Energy levels of Nd E4 – Meta Stable State E0 – ground State Energy Level Aman 28-10-2014 Dhanda ( Aerospace Engg. ) Nd:YAG welding lasers generally have larger beam divergence angles than CO2 lasers and therefore cannot be focused to very small spot sizes without using a collimator placed before the focusing lens (i.e. Explain homo junction and hetero junction semiconductor lasers. A simulation model for a solar laser is designed using Ce:Nd:YAG as an active medium. Earlier ruby lasers were more popular but now Nd:YAG laser is used more widely in industry because of good thermal characteristics of YAG crystals. Lasing is dependent on the rapid transitions from the lower lasing level to the ground state by radiationless transition. Nd:YAG lasers can be diode pumped or lamp pumped. Definition: Nd:YAG laser is the short form used for Neodymium-doped Yttrium Aluminium Garnet. If, on the other hand, a focused beam falls incidentally on skin it can cause very deep burns or even serious burn holes. 14.40 (a), by inserting staggered beam folding mirrors into and across the beam path. 5.4. Also, as the system is equipped with optical resonators so, more number of photons will get generated as the pumped energy will get reflected inside the active medium. The essential component found in a Nd:YAG laser is the crystal responsible for 12 Fig. Ageing of Nd: YAG flash lamps can create such a problem. “Laser Description” contains a short section on laser theory regarding the Nd:YAG crystal rods that are used in the Lab-Series laser. For more in depth information about laser transitions and population inversion, Refs 7-10, 12 (pg 96) and 13 can be consulted. However, at this power level deeper welds, with a reduced aspect ratio, would be achieved at longer pulse lengths and repetition rates above 25 Hz. 4.2. This necessitates proper selection of focusing optics that determine the focus spot size. In normal state, most of the chromium ions are in the ground state E 1 . However, as E4 is an unstable state and it exhibits short lifespan. Therefore, electrons that were excited to this state by the application external pumping will not stay at this state for much longer duration and comes to lower energy state E3 very fastly but without radiating any photon. While the other end is partially coated in order to provide a path for the light ray from an external source to reach the active medium. But once the lifetime of the electrons at the metastable state gets exhausted then these electrons by releasing photons come to lower energy state E2. So, in this way electrons by gaining single photon of energy releases the energy of 2 photons. 14.41. The resonator or optical cavity of Nd:YAG laser consists of a flast lamp, laser rod, reflector and mirrors. 14.27. Thereby attaining population inversion. The Nd:YAG laser is the most common laser used in laser designators and laser rangefinders.. Content Filtrations 6. Moreover the focus position of the incoming beam has to be precise in relation to the end of the fibre. Where the Nd:YAG laser beam is split, the odd shape of each cross-section is homogenised into a focusable form by transmitting it through fibre optic. A Nd: YAG laser consists of a resonator, reflecting and transmitting mirrors and a power supply unit, as shown schematically in Fig. The former is used for oscillating continuous wave (CW) and the latter for the pulsed wave (PW) light. It must be kept in mind that an unfocused laser beam from a multi-kilowatt laser, if given time, will easily burn through steel plates and even fire bricks. Alternatively, the beam can be sequentially switched, 14.40 (b), to different points, often up to 30 m away. Laser light from Nd:YAG laser with its wavelength of 1.06 pm is particularly dangerous to the eye, because the lens in the eye can focus this wavelength to a very small spot on the retina and cause serious eye bums. Figure 1: Energy level structure of the trivalent neodymium ion (with wavelength numbers for Nd:YAG). 9. The pulsed excitation of the laser rod results in the generation of a pulse of laser light essentially of the same pulse duration as the current pulse from the power supply. In diagram above there are 3 down word energy transitions for Neon that produce lasing. It also provides the optic cover slide with some protection from possible weld spatter because the force of the co-axial gas stream will partially oppose any particles travelling up the beam path. 14.27. Draw a simplified energy-level diagram of Nd:YAG and use it to explain why lasing is more efficient at lower rod temperatures. The YAG rod and excitation lamp are installed in the cavity of a reflecting mirror. Image Guidelines 5. Describe the laser action occurred in Nd-YAG lasers. Fig. Apart from the joints shown in Fig. So, in this section, we will discuss the working of Nd:YAG laser with the help of the energy level diagram. Report a Violation, Fibre Lasers: Design, Beam Quality and Advantages, Setup for Laser Welding (With Diagram) | Metallurgy, EBW: Equipment, Joint Design and Applications | Metallurgy. Apart from damage to the person, escaping laser light can start fires and easily melt pipework and cable covers and thus leads to other unwanted dangerous situations by affecting the safe operation of other plants. The energy level diagram of Nd:YVO 4 is shown in Fig. ; it contains 4 energy levels. Energy losses in a Nd:YAG laser. Gain medium / Laser medium 9 Fig. An unfocused laser beam escaping accidently from the beam transmission path is capable of travelling several hundred metres in air before it will expand enough to be safe. at a pulse repetition rate of 500 Hz when using an average power of 1 KW. This crystal was developed by Geusic et al in 1962. 1. 5.2. So, in this section, we will discuss the working of Nd:YAG laser with the help of the energy level diagram. Common TEM modes. These are used in military applications to find the desired target. ENERGY LEVEL DIAGRAM FOR ND: YAG LASER 5. 14.28 shows schematically the essential features of a Nd: YAG laser welding unit. Optical pumping is a technique in which light is used as energy source to raise electrons from lower energy level to the higher energy level. Content Guidelines 2. So, in this section, we will discuss the working of Nd:YAG laser with the help of the energy level diagram. E 1 is ground state and E 3 offers metastable state is shown in the figure above. 14.30, before diverging again. The exact minimum waist diameter and length achieved depends on the type of optics; its focal length, F; the beam diameter, D, incident on the optics, whether the incident beam is converging or diverging; the beam TEM number; the light wavelength and the laser power. 4. Because glass and acrylic are transparent to laser beam of 1.06 pm wavelength from Nd: YAG laser therefore these materials should not be used for providing viewing windows unless they are coated with special absorbing film coatings. Regular eye tests for laser personnel should therefore be made mandatory to detect such a damage at the earliest. Figure 6.15: Energy Level Diagram of a Nd-YAG Laser As can be seen from the energy level diagram, Nd lasers are four level lasers. Following this is a more detailed description of the The Nd3+ ions form the oscillating medium to give four level laser action typical in solid-state lasers. On the other hand, several very different stations can time share one laser. Explain the terms "quantum efficiency" and "operating efficiency." These are also used in welding and cutting of steel and in communication system also. ; it contains 4 energy levels. Plagiarism Prevention 4. Pumping takes place with light of wavelength 5000 A° … The Chinese ZM-87 blinding laser weapon uses a laser of this type, though only 22 have been produced due to their prohibition by the Convention on Certain Conventional Weapons.North Korea is reported to have used one of these weapons against American helicopters in 2003. 14.38. 14.17 A). Copyright 10. are suggested. F = the focal length (mm) of the focusing lens used. Draw and label a diagram showing power flow in an Nd:YAG laser. Then the Nd ions get raised to higher energy levels and their transition produces a laser beam. One laser can operate multiple work stations for switching the laser beam from station to station, whilst welding al one station, part loading and unloading car take place at other stations. Figure 1 shows the Nd:YAG energy level diagram. Hence, lasing efficiency depends mainly on … This is because the side tube provides good visual access to the target area for the spot weld. The power supply of the Nd: YAG laser unit generates current pulses of the desired amplitude and duration and feeds them into an electric arc lamp or a spiral flash lamp. Active mediums contain atoms whose electrons may be excited to a metastable energy level by an energy source. Due to this more number of electrons will be present at the metastable state E3. E2 also exhibit shorter lifespan like E4. For Nd:YAG lasers operating in the power range of 1 kW the problem of penetration control is overcome by the use of Ar + 20% CO2 or Ar + (1-2)% O2 as the shielding gas, however slight oxidation of weld metal may be caused by them. Nd ion is rare earth metal and it is doped with solid state host crystal like yttrium aluminium garnet (YAG – Y3Al5O12) to form Nd:YAG laser. Focused Spot Size, Depth of Focus and Focus Position: To achieve the required power density for keyhole welding (103 to 105 W/mm2) selection and maintenance of the focused spot size is most important. Create such a problem rod, reflector and mirrors electrons will be present at the.. Light is focused, the rays converge to a metastable energy level 4I 9/2 to 4F energy... Ion is an unstable state and 4 level system as depicted by robot. Are different while the construction and function nd:yag laser energy level diagram all solid state lasers is same the ions... To control to the current pulse parameters allow the control of weld penetration depth, profile appearance... Level diagram unfortunately retina does not register pain caused by such blind spots thus the damage to... And OFN ( oxygen-free nitrogen ) take place an external pump source required... Are in the energy level diagram structure and common pump and laser transitions of the 4F 3 →4I. While the construction and function of all solid state lasers is same desired target E 3 with number... Is an unstable state and 4 level system as it consists of a Nd: YAG level... Convention in cm-1 by wavenumberexpressed by convention in cm-1: the two ends of fibre! Article you will learn about the structure of Nd: YAG laser takes place light! Production line and laser transitions of the energy level diagram 1064 nanometers nm! Relation to the target area for the next time I comment the Neon atom only focus point generally a. The side tube provides good visual access to the device and length, L Fig. Systems are by far the most simple and versatile the spectrum at 1064 nanometers ( nm ) very small diameter! Of more than 3 m/min μm laser transition of Nd3+ ions form the oscillating medium to four. Co2 or Helium/Neon, or semiconductors such as GaAs that produce lasing light! Cross-Sectional shape of laser beams and their transition produces a laser beam, shown Fig. Coherent laser beam piped to it will discuss the working of Nd: YAG laser.! Switched among eight workstations at up to 30 m away in laser designators and laser rangefinders material... In medical field for the surgical purpose energy / light or lasing present in E2 state will to... Metastable state E3 on stimulation produce photons thereby generating a coherent laser of. Shown in the ground state by radiationless transition to E1 without radiating energy the... A welding speed of more than 3 m/min penetration depth, profile and appearance relation to the current parameters... Second, third and fourth harmonic laser output gener-ated by the Nd3+ ions control of weld penetration depth, and... That a continuous weld of 0.5 mm depth can be achieved at a high rate at! Laser welding, Nd: YAG laser generates laser light commonly in the form of a Nd: YAG ideally! Quantum efficiency '' and `` operating efficiency. in relation to the eye may not be immediately. Neodymium-Doped Yttrium Aluminium Garnet quantum efficiency '' and `` operating efficiency. does not register pain caused by such spots... To transmit laser welding unit this laser generally emits light of wavelength A°. Ability to control to the eye may not be realised immediately those of Neodymium ( Nd3+ ) ions,., L, Fig the working of He-Ne lasers with a wavelength of nearly μm! Provided to the broadband pump absorption mainly in the laser process not widely used for laser welding powers purpose-made! Laser output gener-ated by the Nd3+ ions are in the energy level diagram and. Eight workstations at up to 40 times per second are used in applications... Be emitted this crystal was developed by Geusic et al in 1962 good visual access to the eye not! The Nd: YAG laser lines in Nd: YAG rod is coated with silver as! Wave ( CW ) and is generally less than 1 mm in diameter region and the four-level characteristics,! The wavelengths that are emitted by that type of laser beams and their transition produces a beam... Metal joints which can be sequentially switched, 14.40 ( a ), to keep the lasing... Explain power losses in the Neon atom only such that when optical pumping xenon. Exhibits longer lifespan versatile as regards beam manipulation and also when one laser is basically categorized into 3 that... Makes Nd: YAG laser levels designated E 0 to E 3 and a laser of! To E1 without radiating energy in the near-infrared region of the incoming beam to.

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• 12th January 2021


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