The changes in the real and imaginary parts of the index of refraction of germanium have been measured at 6943 Å as a function of incident power up to 5 MW/cm2. The results indicate that for nanosecond pulses the primary cause of the change is heating with temperature changes of up to 350°C. In addition, a diffraction grating formed on the surface by interference between the intense beam and a probing beam produces an additional effective change in reflectivity as well as a spatially separated diffracted beam. It is shown that, for a grating spacing of 20 μm, transverse diffusion effects cause no degradation in the effectiveness of the grating.
© 1978 Optical Society of America
T. A. Wiggins, J. A. Bellay, and A. H. Carrieri, "Refractive index changes in germanium due to intense radiation," Appl. Opt. 17, 526-530 (1978)