Laser heat affected zone

As in the case of many metal—ahoy systems, weld ductihty is not as good as that of the base metal. Satisfactory welds can be made in vanadium ahoys provided the fusion zone and the heat-affected zone (HAZ) are protected from contamination during welding. Satisfactory welds can be made by a variety of weld methods, including electron-beam and tungsten-inert-gas (TIG) methods. It is also likely that satisfactory welds can be made by advanced methods, eg, laser and plasma techniques (see Lasers Plasma technology). 

Fig. 11 Scheme of pulse laser ablation. I(r) spatial intensity distribution, r. spatial coordinate, t pulse duration, HAZ heat-affected zone, SAZ shock-affected zone... 

Femtosecond laser irradiation of polymers allows direct structuring of polymers that are transparent at most laser wavelengths (e.g. Teflon), and reveal structures with high quality and a very small heat affected zone (HAZ). Similarities and differences between the ablation of polymers and dielectrics are shown, together with the influence of the pulse duration and band-gap of the materials. Various potential applications in medicine and biosensoric are discussed. 

Laser ablation with laser pulses in the femtosecond (fs) range yields unique advantages, that is, negligible heat affected zone, lower ablation threshold fluence, plasma shielding is not an issue, and the possibility to structure materials that are transparent at the irradiation wavelength. 

Laser cutting focuses the required energy into a very small, dense spot, reducing the heat-affected zone to a minimum area. 

The heat-affected zone (HAZ) is the area of the workpiece adjacent to the kerf where the characteristics of the material have been altered by the heat generated by the laser beam. An advantage of cutting with a laser beam is the small amount of heat transferred to the surrounding area of the workpiece. (See Fig. 25.)... 

The laser deposition process epitaxially generates coarse columnar crystals, and laser remelting reduces the microhardness of the selective laser melting substrate in the 2 mm to 3 mm thick grain increased heat affected zone (31). 

A small heat-affected zone can be achieved with laser welding, which is particularly critical for the miniaturized implantable medical device, where too much heating or the close proximity of the heating zone might cause damage to the components inside the package. 

Glasses can also be processed using the third harmonic of an Nd YAG laser, which results in a reduction of the heat-affected zone and no other damage occurs in the glass [241]. Caused by the wavelength of this frequency converted 355 nm Nd YAG laser operating at a photon energy of 3.5 eV, it is possible to induce not only a thermal processes but also partially photochemical processes. This laser can be focused to a spot size of 1-2 pm. 

Laser Transmission Welding (LTW) is a non-contact joining process with no relative part movement, small heat-affected zone, and minimum flash [1, 2, 3, 4], It is a flexible and precise welding process that is increasingly used to join plastic parts. Hi -power diode lasers are the primary choice for LTW because of their high efficiency, compactness and relatively low cost per watt output of photon energy. 

Compared to alternative joining methods the contact free method has the advantage that hardly any flash or no flash is being produced, which means that joints with a high quality visual appearance can be produced. The laser is clearly superior to alternative processes, even for joining 3D geometries produced by coupling to a robot. The heat-affected zone is only a few pm deep and reduces the risk of surface flaws. 

The parameters, which affect on the results of micropipette pulling process, are naturally the laser power, the size of heated zone and the pulling force. In the figure 3 we show the different micropipettes received at different heated zone. 

Silicate glass was textured using a CO2 laser [330]. The texturing is used to fabricate computer discs of high specific information density made from glass substrates. Laser pulses create a nanotexture on a surface of a glass disc. The process is based on rapid thermal cycles to manipulate the transformation temperature and finally the microstructure of the glass in the zone affected by the heat. 

---