Isolation of high-power multiline CO2 laser amplifier chains from the target reflection

Measurements at Los Alamos Scientific Laboratories have shown1 that, when a high energy (larger than 5G) nanosecond pulse at 10.6 μm is focused into a target, 5% of the incident energy is back-scattered into the laser source. (The measurements were performed at grazing incidence.) As the reflected pulse propagates back into the amplifier chain, its intensity will increase because of (1) the residual gain of the amplifiers and (2) the converging (for the direction of the reflected pulse) optic of the chain. The latter mechanism alone is sufficient to lead to destruction of components in the optical chain since the ratio of the oscillator to the amplifier diameter is about 10−1.