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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. The necessary gas flow rate is mainly dependent on the laser power. 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. 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. Use the above diagram to explain power losses in the laser. Pumping takes place with light of wavelength 5000 A° … Figure 8 shows the energy-level diagram of a Nd:YAG laser. At powers from 3 to 5 kW, rates of 15-30 lit/min, and for those between 5 and 10 kW rates of 25 to 40 lit/min. TOS 7. Lamp pumping is possible due to the broadband pump absorption mainly in the 800-nm region and the four-level characteristics. Active mediums contain atoms whose electrons may be excited to a metastable energy level by an energy source. Lasing is dependent on the rapid transitions from the lower lasing level to the ground state by radiationless transition. 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. 14.27. Energy level diagram: ! Its thermal conductivity is 10 times that of glass. 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. ) Figure 1: Energy level structure and common pump and laser transitions of the trivalent neodymium ion in Nd 3+:YAG. 5.1. The common shielding gases used for laser welding are argon, CO2, helium and OFN (oxygen-free nitrogen). A simplified energy-level scheme for Nd:YAG is shown in Fig. The incident beam diameter, Fig. Ageing of Nd: YAG flash lamps can create such a problem. 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. 3. 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. The laser rod is an Yttrium aluminium garnet (YAG) consisting of Y3A15O12 isometric crystal implanted with carefully distributed 1 % neodymium (Nd) ions. However, initially, electrons in E1 is very much higher as compared to E4. 3. On the other hand, several very different stations can time share one laser. The shape of the cavity is an elliptical cylinder or a double ellipsoid; some typical cavities used in practice are shown, in Fig. When light is focused, the rays converge to a very small waist diameter, d, and length, L, Fig. Alternatively, the beam can be sequentially switched, 14.40 (b), to different points, often up to 30 m away. 14.41. ... (Nd:YAG) crystal is used as the lasing material, light with a wavelength of 1064 nm will be emitted. Nd:YAG laser is very versatile as regards beam manipulation and also when one laser is required to work multiple work stations. When making continuous seam and butt welds an annular skirt shield co-axial with the laser beam, shown in Fig. In this way, several electrons on stimulation produce photons thereby generating a coherent laser beam of 1.064 µm. Energy diagram: The simplified energy level diagram of chromium ions in a ruby laser, indicating appropriate excitation an decay is shown in Fig. 12 Fig. It is a 4 level systems i.e. 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. 1.Process A indicates the traditional 808 nm pumping. 14.17 A). Unfortunately retina does not register pain caused by such blind spots thus the damage caused to the eye may not be realised immediately. 1. 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 … Required fields are marked *. 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 Four-level energy diagram. For more in depth information about laser transitions and population inversion, Refs 7-10, 12 (pg 96) and 13 can be consulted. Figure 2.18 shows the energy level diagram for Nd: YAG laser. 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. 8 Fig. 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. The wavelength (in m) corresponding to a transition between levels 1 and 2 is obtained from:. Explain the construction and working of He-Ne lasers with a suitable energy level diagram. 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 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. Copyright 10. Energy losses in a Nd:YAG laser. 14.33, is however more practical where the laser gun is manipulated by a robot. Amongst the solid-state lasers, Nd:YAG is now most popular for use in welding. “Laser Description” contains a short section on laser theory regarding the Nd:YAG crystal rods that are used in the Lab-Series laser. The multi-mode beam from an Nd: YAG laser can be split, Fig. Co-axial nozzle shielding device, shown in Fig. The energy state E3 is the metastable state and exhibits longer lifespan. 14.27. 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. 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. 14.28 shows schematically the essential features of a Nd: YAG laser welding unit. 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. are suggested. To make deep and narrow welds at high speeds, short pulse widths are required. Then the electrons present in the energy state E1 gains energy and moves to energy state E4. 14.38. Moreover, the laser can be positioned some distance from the production line and laser beam piped to it. a telescope in reverse). Some analysers display only two dimensional picture of the beam profile, however more recent analysers have the ability to display, with the aid of computer graphics, three dimensional isometric picture, as shown in Fig. So, in this section, we will discuss the working of Nd:YAG laser with the help of the energy level diagram. 1.4: Relevant energy levels of Nd-YAG for optical pumping with laser diodes having wavelengths around 805 nm Some energy levels of the Nd atom are illustrated in Fig. 14.29. An unfocused high power laser beam of several mm diameter if incident on the body could maim one for life. 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. Four-Level characteristics lasing material, light with a wavelength of nearly 1.064 μm 1 E! Publishing your articles on this site, please read the following pages: 1 moreover the! 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Different points, often up to 30 m away site, please read the following pages 1! 1 mm in diameter share one laser the fibre laser, Nd: YAG is now nd:yag laser energy level diagram popular use. A photographic print solar laser is a more detailed description of the incoming has...

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