THz commensurate echoes: Periodic rephasing of molecular transitions in free-induction decay.

摘要: We report the first study of coherent transients excited by ultrafast pulses THz radiation. Using a newly developed optoelectronic source well-collimated beams subpicosecond radiation to excite ${\mathrm{N}}_{2}$O vapor, we have observed subsequent emission from vapor pulse trains extending as long 1 nsec. The origin these is periodic rephasing, during free-induction decay, more than fifty coherently rotational lines with commensurate transition frequencies. term this new phenomenon ``THz echoes.'' echo repetition rate equal frequency spacing between adjacent lines. From decay and reshaping echoes relaxation time ${\mathit{T}}_{2}$ anharmonicity factor for molecule are evaluated.