To date, flash lamps have been widely used as the light source for pumping laser material. However, this practice has posed significant technical problems due to their broad spectral bandwidth, low oscillation efficiency, unwieldy equipment size, inability to oscillate at high power and high repetition rate, and unsatisfactory beam quality. It has therefore been recognized that a laser pumped by a laser-diode would achieve oscillation at a high repetition rate and high beam quality, and enable a decrease in equipment size (Fig. 5-6). However, distortion of the laser beam caused by the heating of the laser material and limited laser-diode output power posed problems.
These problems have been solved by 1) eliminating unneeded light focusing and correcting distortion in the polarized condition as well as by developing an amplification technique capable of extracting the stored energy in the laser material without loss, which allows high efficiency and high output power, 2) advancing phase conjugate mirror technology to correct the distortion of the high power laser light, and 3) efficiently removing the heat generated in the laser-diode. By using these technologies, it was possible to achieve better performance and smaller size of the high-power laser. An average power of 360 W was realized with a compact table-top system (Fig. 5-7). This is the world's highest power single-amplifier Nd:YAG laser. A high repetition rate, 1000 times per second, and a high beam quality, close to the theoretical limit, were also achieved (Fig. 5-8).
The newly developed Nd:YAG laser makes possible a tenfold or higher increase in the efficiency of the high-power laser, a hundredfold or higher increase in the repetition rate, and a decrease in component size of one fifth or smaller. These improvements in the Nd:YAG laser are expected to promote its use in industry for such processes as welding, cutting, and machining (removing material) at high speeds and with high accuracy.
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