Abstract

A novel time-resolved spectroscopy is demonstrated using coherent propagation of ultrashort infrared pulses in the limiting case of small peak amplitudes. Drastic changes of the shape of the resonantly tuned pulses occur depending on several parameters; e.g. input pulse duration t_p, molecular dephasing time T₂ and normalized absorption length α_ℓ.^1,2 A detailed theoretical analysis has been carried out revealing several novel features of the phenomenon: (i) The influence of frequency detuning Δω of the input pulse is found to be significant. For quantitative applications frequency resonance has to be adjusted with |Δωt_p| ≲ .5. For pulses of several picoseconds duration the frequency setting has to be highly accurate within ± 1 cm^–1. (ii) The situation for small absorption length (α_ℓ < 1) is discussed in detail. The pulse displays a weak trailing wing with monotonic decay over large time intervals (in contrast to the complex time dependence for α_ℓ >> 1) so that T₂ can be readily determined.

© 1984 Optical Society of America