2015, Pavlov, S.G., Deßmann, N., Pohl, A., Abrosimov, N.V., Mittendorff, M., Winnerl, S., Zhukavin, R.K, Tsyplenkov, V.V., Shengurov, D.V., Shastin, V.N., Hübers, H.-W.

Ultrafast, ultra-broad-band photoconductive detector based on heavily doped and highly compensated germanium has been demonstrated. Such a material demonstrates optical sensitivity in the more than 8 octaves, in the infrared, from about 2 mm to about 8 μm. The spectral sensitivity peaks up between 2 THz and 2.5 THz and is slowly reduced towards lower and higher frequencies. The life times of free electrons/holes measured by a pump-probe technique approach a few tenths of picoseconds and remain almost independent on the optical input intensity and on the temperature of a detector in the operation range. During operation, a detector is cooled down to liquid helium temperature but has been approved to detect, with a reduced sensitivity, up to liquid nitrogen temperature. The response time is shorter than 200 ps that is significantly faster than previously reported times.

2020, Pavlov, S.G., Deßmann, N., Pohl, A., Zhukavin, R.K., Klaassen, T.O., Abrosimov, N.V., Riemann, H., Redlich, B., Van Der Meer, A.F.G., Ortega, J.-M., Prazeres, R., Orlova, E.E., Muraviev, A.V., Shastin, V.N., Hübers, H.-W.

Transient-type stimulated emission in the terahertz (THz) frequency range has been achieved from phosphorus doped silicon crystals under optical excitation by a few-picosecond-long pulses generated by the infrared free electron lasers FELIX and CLIO. The analysis of the lasing threshold and emission spectra indicates that the stimulated emission occurs due to combined population inversion based lasing and stimulated Raman scattering. Giant gain has been obtained in the optically pumped silicon due to large THz cross sections of intracenter impurity transitions and resonant intracenter electronic scattering. The transient-type emission is formed under conditions when the pump pulse intervals exceed significantly the photon lifetime in the laser resonator. © 2020 Author(s).