High-resolution time resolved spectroscopy of collisionless molecular beams: optical T_1 and T_2
We report on the observation of the coherent and incoherent transients of collisionless molecular beams using single-mode laser spectroscopy. The technique offers a resolution of one part in 10^8, and resolves the spectra on the time scale of nanoseconds. The methods is demonstrated on an effusive beam of iodine. Since the beam is collisionless the optical dephasing of the selectively excited (10^(−4) cm^(−1)) molecular packet can be directly related to the zero-pressure optical T_1 obtained from the Stern-Volmer relationship of iodine gas in a bulb. Finally, the cross section for the radiationless and radiative deactivation are reported and related to the free-induction decay (FID) of the coherently excited molecular beam.