Reflectivity changes of Ge and the efficiency of moving diffraction gratings

Reflectivity changes and the efficiency of a temporary grating formed on a Ge surface by two beams, which differ in frequency by 26 MHz, are compared with those measured for beams of equal frequency. The results indicate that the observations can be explained by a deterioration in the quality of the grating due to its motion across the surface. The predicted effects due to a phase difference between the intensity pattern and the temperature variation on the surface which it produces were not observed.