Passive anti-return device for high power ruby laser

The high power ruby lasers with an amplifier chain must be protected of the light returns towards the oscillator. After description of the most used devices, we show that it is possible to use a process mixing an saturable absorber and a prism polarizer followed by a plate retarder. We are leading to observe again the transmission curves of saturable glasses RG715 type from Schott, versus lightning and time. The transmission factors derived from this studies are compared to be measures done with a 80 MW ruby laser. With anti-reflection coatings on the optical elements, the transmission factor of the direct laser wave is 75% whereas the extinction ratio of the return wave is 2.10-5.