Tunable far-infrared laser theory: the dressed-atom approach (A)

Chang-Xin Wang, Runwen Wang, Ensheng Fu

Ulrich D. Jentschura, Christoph H. Keitel

Changxin Wang, Ensheng Fu, Runwen Wang

The dressed-atom approach is used to analyze saturation in an optically pumped three-level system. The small-signal gain is found for the case when two different saturation factors are present, and the result can be conveniently applied to analyze the different saturation behavior of the Raman and line-center transitions in optically pumped far-infrared lasers.

C. J. Joachain

G. M. Lankhuijzen, Marcel Drabbels, F. Robicheaux +1 more

Transitions from bound atomic Rydberg Stark states in a static electric field to autoionizing Rydberg states above the electric-field-induced ionization threshold are studied using a broadband, tunable free-electron laser (photon energy 160--1400 ${\mathrm{cm}}^{\ensuremath{-}1}$, pulse duration $\ensuremath{\sim}1$ ps) and compared with multichannel quantum defect theory calculations. An atomic streak camera is used to record the time-resolved electron emission transients of the autoionizing atoms. For Stark states located on the downfield side of the potential, the far-infrared ionization spectrum is found to be smooth and the electron emission prompt $(<2$ ps), whereas for Stark states located on the upfield side, the far-infrared spectrum has sharp resonances, and the lifetime of the quasicontinuum states is considerably longer. The electron-emission transients from optical ionization of ground-state atoms are compared to transients from far-infrared ionization of Rydberg atoms, showing that the angular motion of the wave packet is responsible for the ionization dynamics for both cases, but different coherent superpositions of angular momentum states are excited depending on the initial state. Finally, we discuss the feasability of using Rydberg atoms as an ultrafast far-infrared detector, starting from a downfield state, or as a wavelength-selective detector, starting from an upfield state.

Vladimir A. Kukushkin

A quantum dot-based laser with a frequency continuously tunable in the far-infrared and terahertz ranges via varying the optical pumping intensity is suggested. Its operation is possible at room temperature and is based on the inversionless amplification mechanism in the proposed modified three-level ladder scheme, where the pumping frequency is equal to the frequency of a dipole-forbidden transition from the ground state to the second excited state.