Tunable cyclotron-resonance laser in germanium

We report strong narrow-band stimulated far-infrared cyclotron-resonance emission from the light holes in germanium in crossed electric and magnetic fields. The emission spectrum consists of a single line which is linearly tunable with magnetic field. The gain of the cyclotron-resonance laser is determined to be 0.05±0.02 ${\mathrm{cm}}^{\mathrm{-}1}$. For the first time we have identified the lasing transition to be the n=2 to n=1 Landau-level transition of the b-set light holes by a comparison of absorption and emission spectra with calculations of the band structure including nonparabolicity corrections.