Three level laser energy diagram. This type of laser also finds its application in medical field for the surgical purpose. The ability to control to the current pulse parameters allow the control of weld penetration depth, profile and appearance. Helium Neon Laser Energy Level Diagram Here upward transition shows the absorption of energy from the pumping source by Helium atom. The neodymium ion (Nd3+) in the YAG matrix (Y3Al5O12, yttrium aluminium garnet) has a great many levels that can give different laser transitions. Figure 2.18 shows the energy level diagram for Nd: YAG laser. Figure 10. Common TEM modes. ... (Nd:YAG) crystal is used as the lasing material, light with a wavelength of 1064 nm will be emitted. For more in depth information about laser transitions and population inversion, Refs 7-10, 12 (pg 96) and 13 can be consulted. 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 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. Thereby attaining population inversion. Nd:YAG lasers can be diode pumped or lamp pumped. 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. These are also used in welding and cutting of steel and in communication system also. 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. 14.32 gives reliable weld protection. Explain the terms "quantum efficiency" and "operating efficiency." The figure below shows the 4 state energy level diagram of Nd:YAG laser: Here, E 1 is the lowest energy state while E 4 is the highest Simplified diagram showing transitions for Nd 3 + in a Nd:YAG laser. 5.4. 14.30, before diverging again. 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 simulation model for a solar laser is designed using Ce:Nd:YAG as an active medium. Fig. Hence, lasing efficiency depends mainly on … 14.35 while Fig. Continuous oscillation is possible with YAG. It is a 4 level systems i.e. 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. Its working principle is such that when optical pumping is provided to the device. 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. This necessitates proper selection of focusing optics that determine the focus spot size. So, in this way electrons by gaining single photon of energy releases the energy of 2 photons. 14.34. In normal state, most of the chromium ions are in the ground state E 1 . 2. 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. Table 1 illustrates various types of material currently used for lasing and the wavelengths that are emitted by that type of laser. The necessary gas flow rate is mainly dependent on the laser power. The multi-mode beam from an Nd: YAG laser can be split, Fig. Ageing of Nd: YAG flash lamps can create such a problem. 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. Differentiate He-Ne, Nd-YAG and Semiconductor lasers. 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. Basically, as a source of optical pumping, xenon or krypton flash tube is taken in its case. Copyright 10. The common shielding gases used for laser welding are argon, CO2, helium and OFN (oxygen-free nitrogen). So, in this section, we will discuss the working of Nd:YAG laser with the help of the energy level diagram. 4. F = the focal length (mm) of the focusing lens used. The precise distance depends on the focus f number; the lower the number the greater the rate of beam expansion. Before publishing your articles on this site, please read the following pages: 1. However, a focused beam expands much faster beyond the focus point generally reaching a safe diameter after a few metres. 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. 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. So, in this section, we will discuss the working of Nd:YAG laser with the help of the energy level diagram. Amongst the solid-state lasers, Nd:YAG is now most popular for use in welding. There are industrial micro-spot welding systems where the beam is switched among eight workstations at up to 40 times per second. The optical fibre material is SiO2 (quartz) and is generally less than 1 mm in diameter. 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. 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. Process B indicates the 879 nm direct pumping which is to pump laser active ions from the Z 1 … The optical fibre assemblies used to transmit laser welding powers are purpose-made and quite different from those used in electronics. Beam transmission efficiency is also impaired if the fibre is bent too tightly. Thereby forming an optical cavity. When the rod temperature is low, these transitions will occur at a high rate. The YAG rod and excitation lamp are installed in the cavity of a reflecting mirror. But when making a continuous seam or butt welds with overlapping spots Ar or OFN is generally used for lasers rated up to 300 W. Above this power level gas shielding becomes more critical and can affect penetration depth and appearance. 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. 14.28 shows schematically the essential features of a Nd: YAG laser welding unit. 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. 14.41. Regular eye tests for laser personnel should therefore be made mandatory to detect such a damage at the earliest. APPLICATIONS • Used widely in medical field. It is a 4 level systems i.e. 14.36 shows the basic sheet metal joints which can be laser welded. TOS 7. Active mediums contain atoms whose electrons may be excited to a metastable energy level by an energy source. It is a solid state and 4 level system as it consists of 4 energy levels. Working of Nd:YAG laser. Prohibited Content 3. If, on the other hand, a focused beam falls incidentally on skin it can cause very deep burns or even serious burn holes. Lasing is dependent on the rapid transitions from the lower lasing level to the ground state by radiationless transition. An unfocused high power laser beam of several mm diameter if incident on the body could maim one for life. The fibre optic beam delivery systems are by far the most simple and versatile. ND YAG laser working diagram. Laser beam analysers are used to examine the cross-sectional shape of laser beams and their mode structures. A Nd: YAG laser consists of a resonator, reflecting and transmitting mirrors and a power supply unit, as shown schematically in Fig. This ability means that the laser beam can travel directly from the laser unit through a flexible cable to a laser gun mounted on an articulated wrist of a robot arm, Fig. 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. 5:50. This laser generally emits light of wavelength of nearly 1.064 μm. The approximate focused spot size for these lasers is usually estimated from the following formula: θ = the divergence angle (radians) of the laser beam as it leaves the laser or collimator. Construction and working of Nd YAG laser - Duration: ... winnerscience 54,739 views. However, one end is completely coated with silver so as to achieve maximum light reflection. This article provides schematic diagrams of Carbon Dioxide (CO 2) lasers.. The 1.064 and 1.061-μm transitions, provide the lowest threshold laser lines in Nd:YAG. 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. Also included is a discussion of the second, third and fourth harmonic laser output gener-ated by the system. When using a correctly positioned coaxial or side tube shielding device. The shape of the cavity is an elliptical cylinder or a double ellipsoid; some typical cavities used in practice are shown, in Fig. 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. A hazard may also arise due to the reflection of a focused beam from the surface of the workpiece, particularly if the incident beam is inclined to the workpiece at an angle of less than 70°. Its thermal conductivity is 10 times that of glass. The Nd:YAG rod and the flash tube are placed inside an elliptical cavity so, that maximum produced light can reach the rod. Fig. Figure E1 locates the energy levels by wavenumberexpressed by convention in cm-1. 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. 14.31, is generally used, especially where precision placed spot welds are required. ; it contains 4 energy levels. 8 Fig. The former is used for oscillating continuous wave (CW) and the latter for the pulsed wave (PW) light. After reading this article you will learn about the structure of Nd: YAG laser with the help of suitable diagrams. The Nd 3+ ions form the oscillating medium to give four level laser action typical in solid-state lasers. ; it contains 4 energy levels. 2. 14.27. The energy state E3 is the metastable state and exhibits longer lifespan. E 1 is ground state and E 3 offers metastable state is shown in the figure above. Thus, electrons present in E2 state will come to E1 without radiating energy in the form of a photon. 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. Four-level energy diagram. 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. Due to this more number of electrons will be present at the metastable state E3. * How does Nd:YAG laser work? 14.30, am be established for Nd:YAG lasers by taking a photographic print. Nd:YAG, a four-level system, to keep the lower laser level depopulated. E2 also exhibit shorter lifespan like E4. When making continuous seam and butt welds an annular skirt shield co-axial with the laser beam, shown in Fig. 16 Fig. For Nd: YAG laser welding a simple side tube shielding device, as shown in Fig. Fig. Unless welding speed is paramount, it is best to choose the focused spot size for welding based on f number of 4 for Nd: YAG lasers and 7.5 for CO2 lasers. 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. ) Apart from the joints shown in Fig. 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. 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. The Nd:YAG laser is the most common laser used in laser designators and laser rangefinders.. 3. Due to doping, yttrium ions get replaced by the Nd3+ ions. 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. Definition: Nd:YAG laser is the short form used for Neodymium-doped Yttrium Aluminium Garnet. Save my name, email, and website in this browser for the next time I comment. 14.21, Nd: YAG laser welding can be applied to most of the basic joint configurations in plates and pipes, as shown in Fig. 1.Process A indicates the traditional 808 nm pumping. It is a 4 level systems i.e. In this way, several electrons on stimulation produce photons thereby generating a coherent laser beam of 1.064 µm. 14.38. [enter image description here] The energy levels E 1, E 2 and E 3 of Nd along with many other levels of YAG. Energy diagram: The simplified energy level diagram of chromium ions in a ruby laser, indicating appropriate excitation an decay is shown in Fig. 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. The λ=1.06 μm laser transition is the strongest of the 4F 3 /2 →4I 11 /2 transitions. 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. These are used in military applications to find the desired target. Describe the laser action occurred in Nd-YAG lasers. 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. The Nd:YAG laser is a four-level system as depicted by a simplified energy level diagram in and Figure 2. 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. So, the electrons in this particular state will last for a longer duration. Moreover, the laser can be positioned some distance from the production line and laser beam piped to it. 4. This crystal was developed by Geusic et al in 1962. Draw a simplified energy-level diagram of Nd:YAG and use it to explain why lasing is more efficient at lower rod temperatures. Nd:YAG, liquid dyes, gases like CO2 or Helium/Neon, or semiconductors such as GaAs. While down ward transition shows the emission of energy / light or lasing present in the Neon atom only. 5.3. Nd ions have two absorption band, and excitation is done by optical pumping, either by flash lamps for pulsed lasers, or by arc lamps for continuous wave lasers. 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.. 14.26. The laser rod is an Yttrium aluminium garnet (YAG) consisting of Y3A15O12 isometric crystal implanted with carefully distributed 1 % neodymium (Nd) ions. Energy losses in a Nd:YAG laser. Your email address will not be published. For example a gas (low rate of 10 to 20 lit/min. 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