Observation of destructive interference in the radiation loss of second order distributed feedback lasers.

We report measurement of the distribution of 90 degree radiation loss along the length of an optically pumped distributed feedback resonator having a second order grating and nonreflecting ends. The loss is strong at the ends, but nearly cancels at the center due to destructive interference of the scattered radiation from the oppositely propagating waves forming the lasing mode. This is the first observation of this interference effect, which provides an important source of single mode selection in distributed feedback lasers with second order gratings.