The U12IR beamline at the National Synchrotron Light Source in Brookhaven National Laboratory is optimized to use the very far infrared portion of the spectrum (down to 0.25 meV - 5 mm). In synchronization to an external pumped laser it is also able to perform sub-nanosecond pump-probe spectroscopy in the whole infrared range. In this talk I am going to discuss two distinct aspects of this beamline:
(i) Solid state pump-probe applications
I am going to show our results on the the Cooper pair dynamics in metallic superconductors and the electron-hole recombination in semiconductors. In both cases the external laser sets the system at an excited state (either by breaking the Cooper pairs or by creating an electron-hole pair) and the synchrotron light probes the relaxation of the system back to its ground state.
(ii) Observation of coherent emission in the microwave region.
The far-infrared optimization of the beamline allowed us to observe, by optical means, an unexpected coherent light emission peaked at 0.7 cm. We propose that this effect is due to a microwave instability with a modulation of the electron bunches. I am going to discuss its characteristics and possible origins.