Temperature-dependent absorptances of ceramics for Nd:YAG and CO2 laser processing applications

Abstract

The absorptance of a material at the laser wavelength and as a function of temperature, ranging from room temperature to the removal point, significantly affects the efficiency of the laser machining process. A priori predictions of a laser machining process, using either simplistic or sophisticated models, requires knowledge of the material's absorptance behavior. An experimental apparatus for such measurements is described. The device consists of a specimen mounted inside an integrating sphere, heated rapidly by a CO 2 or a Nd:YAG laser. Reflectances are measured with a small focused probe laser (Nd:YAG or CO 2), while specimen surface temperatures are recorded by a high-speed pyrometer. Experimental results have been obtained for wavelengths of 1.06 m (Nd:YAG) and 10.6 m (CO 2) for graphite, alumina, hot-pressed silicon nitride, sintered-silicon carbide, as well as two continous-fiber ceramic matrix composites (SiC-based). Data are presented for temperatures between room temperature and the ablation/decomposition points.

Quantitative evaluation of the quality of the cuts performed on mullite-alumina by Nd:YAG laser

“…The absorption mechanism should be explained based on two phenomena: the heterogeneities of the ceramic composite produce scattering of the radiation at grain boundaries and inclusions resulting in a effective multiplication of the light path [21] and strong absorption in the localized lattice defects in the boundaries [22]; secondly, a great increase in the absorptance of alumina at 1064 nm from 20 up to 95% with increasing temperature over melting point has been reported [23].…”

Rapid micro hole laser drilling in ceramic substrates using single mode fiber laser

“…Please note that Zhang and Modest (1996) published experimental results showing that the absorption of alumina at 1064 nm significantly increases to more 90% at temperatures exceeding the melting point. In addition, it is worthwhile to mention that at the emission wavelength of the CO 2 laser, i.e.…”

Laser joining of silicon carbide—a new technology for ultra-high temperature resistant joints

“…The absorption of the solder is not sufficiently known, however, its properties can be compared with those of glass. Oxidic glass materials absorb less than 15% of a wavelength of 1.06 m and more than 80% of a wavelength of 10.6 m. (Zhang and Modest, 1996;Blanke, 1989;Tsarkov et al, 1997).…”

“…Two lasers with different wavelengths have been used: a CO 2 laser with a maximum cw laser beam power of 700 W and a Nd:YAG laser with a maximum cw power of 1000 W. Both wavelengths can be distinguished by their different absorption coefficients (Zhang and Modest, 1996). The CO 2 laser beam has either been defocused to a beam diameter of 3 mm on the material surface or it has been deflected using two scanning mirrors to produce a defined temperature field.…”