On the differences between the beam interaction characteristics of CO 2, Nd:YAG, excimer and high power diode lasers with a SiO 2 /Al 2 O 3 ceramic

By using a number of techniques and approaches certain differences between the beam interaction characteristics of CO 2 laser, a Nd:YAG laser, a high power diode laser (HPDL) and an excimer laser with a SiO 2 /Al 2 O 3 ceramic have been investigated. By employing a derivative of Beer-Lambert's law, the laser beam absorption lengths of the four lasers were calculated as 470 - 22 µm for the CO 2 laser, 195 - 12 µm for the Nd:YAG laser, 177 - 15 µm for the HPDL and 7.5 - 19 µm for the excimer laser. The fluence threshold values at which significant material removal occurs the CO 2 laser, Nd:YAG laser, HPDL and excimer laser were found to be 68, 128, 181 and 0.12 J cm m 2 , respectively. Absorptivity measurements revealed that there is no correlation between the actual absorptivity of the SiO 2 /Al 2 O 3 ceramic and the absorption length for each of the four lasers. The thermal loading values for the CO 2 laser, the, Nd:YAG laser, the HPDL and the excimer laser were determined as 2.57, 6.73, 9.83 and 22.24 kJ cm m 3 , respectively. An examination of the laser induced meltpool propagation in the SiO 2 /Al 2 O 3 ceramic revealed good agreement with the Stefan solution to the diffusion equation for the CO 2 , Nd:YAG and HPDLs.