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The LaserStar | |
Fig.4 High-voltage electricity causes the Flash lamp to emit an intense burst of light, exciting some of the atoms in the crystal to higher energy levels. |
 Fig. 5 At specific energy level, some atoms emit particles of light called photons. At first the photons are emitted in all directions. Photons from one atom stimulate emission of photons from other atoms and the light intensity is rapidly amplified. |
 Fig. 6 Mirrors at each end reflect the photons back and forth, continuing this process of stimulated emission and amplification. |
 Fig. 7 The photons leave through the partially silvered mirror at one end. This is laser light. |
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Figures 4 to 7 show a typical resonator or optical resonant cavity. This is where the flash lamp and the material selected (Nd:YAG crystal) are located. When intensive light is applied to the crystal, via a reflector, it initially produces non-directional light. For optimum utilization of the flash lamp light, both the laser crystal and the flash lamp are arranged just within the "focal point" of an ellipsoidal mirror. A semi-reflecting and a fully reflecting mirror are mounted outside the crystal. Only those parts of the laser light that hit these mirrors and are reflected into the laser crystal can be amplified during the pulse of the flash lamp while passing through the crystal. The amplified laser light has the same properties as the original laser light; i.e. it has the same direction, the same wavelength, the same phase and the same polarization. The mirrors determine the highly directional propagation characteristics of the laser light. Part of the laser light passes through the semi-reflecting mirror and is the laser light that performs the welding function. This process produces a very high energy density light beam, many times higher than is possible with normal light at the focal point of a lens. The energy -"hot light"- created at the focal point in a relatively short time (0.5 to 20 ms) heats the work piece beyond its melting point and thus enables a welding. The area effected is in a limited range of only approximately 0.25 to 2 mm, depending on the material. The laser light welds two metals together and thus permits safe, durable, precise and non-warp joining of parts in the form of a spot or seam. Because of the very short time of the laser pulse the zone of heat influence is limited to the immediate vicinity of the welded spot or seam. The characteristics of a laser pulse and thus the effect on the material can be influenced by the operating parameters VOLTAGE and PULSE LENGTH (width). The voltage has influence on the amplitude; the pulse length influences the width of the laser pulse. In practice the effect of both parameters while welding metals is as follows:
Background The propagation of light through space can be described in terms of a traveling wave motion. The wave is composed of a combination of mutually perpendicular electric and magnetic fields; therefore the direction of propagation of the wave is at right angles to both filed directions. Figure 2 shows an electromagnetic wave Fig. 2 The electromagnetic wave The concept of laser light is better understood by the definition of its properties. Laser light has three properties: monochromatic, coherent, and collimated. When all emitted photons bear constant phase relationship with each other in both time and phase the light is said to be coherent. It is also monochromatic (one color) due to the specificity and purity of the medium used. Last, the light is contained in a very narrow pencil, almost collimated (see figure 3). Fig. 3
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