ABSTRACT
In certain laser applications, the laser beam is often required to possess very high energy (or power). For instance, laser nuclear fusion needs at least an energy as high as ten thousand joules, lidar needs high power modulating laser, etc. But, if high energy laser is desired, it is in general very difficult if just a laser (oscillating) device is used. This is because the requirements on raising the output power (energy) of a laser and the indices (such as the light beam divergence angle, monochromaticity, pulse width, modulating performance, etc.) are contradictory. So, if the excellent characteristics of a laser beam are to be maintained, neither the caliber nor the length of its operation material should be too great. Furthermore, as the laser beam in the laser will pass through the operation back and forth many times, when the output power (energy) is very high, the operation material can be destroyed.
