Researchers from Delft University of Technology in the Netherlands, and the University of California and Lawrence Berkeley National Laboratory in Berkeley, Calif., have reported mode-locked operation in a copper-doped germanium laser. The device, which the group described in the Nov. 13, 2000, issue of Applied Physics Letters, produced coherent radiation from 90 to 120 µm, with pulse lengths as short as 160 ps.

The researchers introduced copper into 5-mm-thick slices of Czochralski-grown germanium by diffusion at 700 °C for 24 hours. They expect to optimize the performance of the laser by varying the concentrations of copper and the crystal orientations.